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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200601021840.k02Ieed21704@candle.pha.pa.us>
Subject: Stats collector performance improvement
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To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 2 Jan 2006 13:40:40 -0500 (EST)
CC: Michael Fuhr <mike@fuhr.org>,
	Merlin Moncure <merlin.moncure@rcsonline.com>,
	Carlos Benkendorf <carlosbenkendorf@yahoo.com.br>,
	PostgreSQL-patches <pgsql-patches@postgresql.org>
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Tom Lane wrote:
> Michael Fuhr <mike@fuhr.org> writes:
> > Further tests show that for this application
> > the killer is stats_command_string, not stats_block_level or
> > stats_row_level.
> 
> I tried it with pgbench -c 10, and got these results:
> 	41% reduction in TPS rate for stats_command_string
> 	9% reduction in TPS rate for stats_block/row_level (any combination)
> 
> strace'ing a backend confirms my belief that stats_block/row_level send
> just one stats message per transaction (at least for the relatively
> small number of tables touched per transaction by pgbench).  However
> stats_command_string sends 14(!) --- there are seven commands per
> pgbench transaction and each results in sending a <command> message and
> later an <IDLE> message.
> 
> Given the rather lackadaisical way in which the stats collector makes
> the data available, it seems like the backends are being much too
> enthusiastic about posting their stats_command_string status
> immediately.  Might be worth thinking about how to cut back the
> overhead by suppressing some of these messages.

I did some research on this because the numbers Tom quotes indicate there
is something wrong in the way we process stats_command_string
statistics.

I made a small test script:
	
	if [ ! -f /tmp/pgstat.sql ]
	then	i=0
		while [ $i -lt 10000 ]
		do
			i=`expr $i + 1`
			echo "SELECT 1;"
		done > /tmp/pgstat.sql
	fi
	
	time sql test </tmp/pgstat.sql >/dev/null

This sends 10,000 "SELECT 1" queries to the backend, and reports the
execution time.  I found that without stats_command_string defined, it
ran in 3.5 seconds.  With stats_command_string defined, it took 5.5
seconds, meaning the command string is causing a 57% slowdown.  That is
way too much considering that the SELECT 1 has to be send from psql to
the backend, parsed, optimized, and executed, and the result returned to
the psql, while stats_command_string only has to send a string to a
backend collector.  There is _no_ way that collector should take 57% of
the time it takes to run the actual query.

With the test program, I tried various options.  The basic code we have
sends a UDP packet to a statistics buffer process, which recv()'s the
packet, puts it into a memory queue buffer, and writes it to a pipe()
that is read by the statistics collector process which processes the
packet.

I tried various ways of speeding up the buffer and collector processes. 
I found if I put a pg_usleep(100) in the buffer process the backend
speed was good, but packets were lost.  What I found worked well was to
do multiple recv() calls in a loop.  The previous code did a select(),
then perhaps a recv() and pipe write() based on the results of the
select().  This caused many small packets to be written to the pipe and
the pipe write overhead seems fairly large.  The best fix I found was to
loop over the recv() call at most 25 times, collecting a group of
packets that can then be sent to the collector in one pipe write.  The
recv() socket is non-blocking, so a zero return indicates there are no
more packets available.  Patch attached.

This change reduced the stats_command_string time from 5.5 to 3.9, which
is closer to the 3.5 seconds with stats_command_string off.

A second improvement I discovered is that the statistics collector is
calling gettimeofday() for every packet received, so it can determine
the timeout for the select() call to write the flat file.  I removed
that behavior and instead used setitimer() to issue a SIGINT every
500ms, which was the original behavior.  This eliminates the
gettimeofday() call and makes the code cleaner.  Second patch attached.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

--ELM1136227240-6886-0_
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Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.116
diff -c -c -r1.116 pgstat.c
*** src/backend/postmaster/pgstat.c	2 Jan 2006 00:58:00 -0000	1.116
--- src/backend/postmaster/pgstat.c	2 Jan 2006 18:36:43 -0000
***************
*** 1911,1916 ****
--- 1911,1918 ----
  	 */
  	for (;;)
  	{
+ loop_again:
+ 
  		FD_ZERO(&rfds);
  		FD_ZERO(&wfds);
  		maxfd = -1;
***************
*** 1970,2014 ****
  		 */
  		if (FD_ISSET(pgStatSock, &rfds))
  		{
! 			len = recv(pgStatSock, (char *) &input_buffer,
! 					   sizeof(PgStat_Msg), 0);
! 			if (len < 0)
! 				ereport(ERROR,
! 						(errcode_for_socket_access(),
! 						 errmsg("could not read statistics message: %m")));
! 
! 			/*
! 			 * We ignore messages that are smaller than our common header
! 			 */
! 			if (len < sizeof(PgStat_MsgHdr))
! 				continue;
! 
! 			/*
! 			 * The received length must match the length in the header
! 			 */
! 			if (input_buffer.msg_hdr.m_size != len)
! 				continue;
! 
  			/*
! 			 * O.K. - we accept this message.  Copy it to the circular
! 			 * msgbuffer.
  			 */
! 			frm = 0;
! 			while (len > 0)
  			{
! 				xfr = PGSTAT_RECVBUFFERSZ - msg_recv;
! 				if (xfr > len)
! 					xfr = len;
! 				Assert(xfr > 0);
! 				memcpy(msgbuffer + msg_recv,
! 					   ((char *) &input_buffer) + frm,
! 					   xfr);
! 				msg_recv += xfr;
! 				if (msg_recv == PGSTAT_RECVBUFFERSZ)
! 					msg_recv = 0;
! 				msg_have += xfr;
! 				frm += xfr;
! 				len -= xfr;
  			}
  		}
  
--- 1972,2033 ----
  		 */
  		if (FD_ISSET(pgStatSock, &rfds))
  		{
! 			int loops = 0;
! 			
  			/*
! 			 *	While pipewrite() can send multiple data packets, recv() pulls
! 			 *	only a single packet per call.  For busy systems, doing
! 			 *	multiple recv() calls and then one pipewrite() can improve
! 			 *	query speed by 40%.  25 was chosen because 25 packets should
! 			 *	easily fit in a single pipewrite() call.  recv()'s socket is
! 			 *	non-blocking.
  			 */
! 			while (++loops < 25 &&
! 				   (len = recv(pgStatSock, (char *) &input_buffer,
! 							   sizeof(PgStat_Msg), 0)) != 0)
  			{
! 				if (len < 0)
! 				{
! 					if (errno == EAGAIN)
! 						continue;
! 					ereport(ERROR,
! 							(errcode_for_socket_access(),
! 							 errmsg("could not read statistics message: %m")));
! 				}
! 	
! 				/*
! 				 * We ignore messages that are smaller than our common header
! 				 */
! 				if (len < sizeof(PgStat_MsgHdr))
! 					goto loop_again;
! 	
! 				/*
! 				 * The received length must match the length in the header
! 				 */
! 				if (input_buffer.msg_hdr.m_size != len)
! 					goto loop_again;
! 	
! 				/*
! 				 * O.K. - we accept this message.  Copy it to the circular
! 				 * msgbuffer.
! 				 */
! 				frm = 0;
! 				while (len > 0)
! 				{
! 					xfr = PGSTAT_RECVBUFFERSZ - msg_recv;
! 					if (xfr > len)
! 						xfr = len;
! 					Assert(xfr > 0);
! 					memcpy(msgbuffer + msg_recv,
! 						   ((char *) &input_buffer) + frm,
! 						   xfr);
! 					msg_recv += xfr;
! 					if (msg_recv == PGSTAT_RECVBUFFERSZ)
! 						msg_recv = 0;
! 					msg_have += xfr;
! 					frm += xfr;
! 					len -= xfr;
! 				}
  			}
  		}
  
***************
*** 2023,2029 ****
  		 * caught up, or because more data arrives so that we have more than
  		 * PIPE_BUF bytes buffered).  This is not good, but is there any way
  		 * around it?  We have no way to tell when the collector has caught
! 		 * up...
  		 */
  		if (FD_ISSET(writePipe, &wfds))
  		{
--- 2042,2048 ----
  		 * caught up, or because more data arrives so that we have more than
  		 * PIPE_BUF bytes buffered).  This is not good, but is there any way
  		 * around it?  We have no way to tell when the collector has caught
! 		 * up.  Followup, the pipe rarely fills up.
  		 */
  		if (FD_ISSET(writePipe, &wfds))
  		{

--ELM1136227240-6886-0_
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Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.116
diff -c -c -r1.116 pgstat.c
*** src/backend/postmaster/pgstat.c	2 Jan 2006 00:58:00 -0000	1.116
--- src/backend/postmaster/pgstat.c	2 Jan 2006 18:21:28 -0000
***************
*** 145,150 ****
--- 145,151 ----
  static PgStat_StatBeEntry *pgStatBeTable = NULL;
  static int	pgStatNumBackends = 0;
  
+ static volatile bool	need_statwrite;
  
  /* ----------
   * Local function forward declarations
***************
*** 164,169 ****
--- 165,171 ----
  
  NON_EXEC_STATIC void PgstatBufferMain(int argc, char *argv[]);
  NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]);
+ static void force_statwrite(SIGNAL_ARGS);
  static void pgstat_recvbuffer(void);
  static void pgstat_exit(SIGNAL_ARGS);
  static void pgstat_die(SIGNAL_ARGS);
***************
*** 1548,1560 ****
  	PgStat_Msg	msg;
  	fd_set		rfds;
  	int			readPipe;
- 	int			nready;
  	int			len = 0;
! 	struct timeval timeout;
! 	struct timeval next_statwrite;
! 	bool		need_statwrite;
  	HASHCTL		hash_ctl;
! 
  	MyProcPid = getpid();		/* reset MyProcPid */
  
  	/*
--- 1550,1560 ----
  	PgStat_Msg	msg;
  	fd_set		rfds;
  	int			readPipe;
  	int			len = 0;
! 	struct itimerval timeval;
  	HASHCTL		hash_ctl;
! 	bool		need_timer = false;
! 	
  	MyProcPid = getpid();		/* reset MyProcPid */
  
  	/*
***************
*** 1572,1578 ****
  	/* kluge to allow buffer process to kill collector; FIXME */
  	pqsignal(SIGQUIT, pgstat_exit);
  #endif
! 	pqsignal(SIGALRM, SIG_IGN);
  	pqsignal(SIGPIPE, SIG_IGN);
  	pqsignal(SIGUSR1, SIG_IGN);
  	pqsignal(SIGUSR2, SIG_IGN);
--- 1572,1578 ----
  	/* kluge to allow buffer process to kill collector; FIXME */
  	pqsignal(SIGQUIT, pgstat_exit);
  #endif
! 	pqsignal(SIGALRM, force_statwrite);
  	pqsignal(SIGPIPE, SIG_IGN);
  	pqsignal(SIGUSR1, SIG_IGN);
  	pqsignal(SIGUSR2, SIG_IGN);
***************
*** 1597,1608 ****
  	init_ps_display("stats collector process", "", "");
  	set_ps_display("");
  
- 	/*
- 	 * Arrange to write the initial status file right away
- 	 */
- 	gettimeofday(&next_statwrite, NULL);
  	need_statwrite = TRUE;
  
  	/*
  	 * Read in an existing statistics stats file or initialize the stats to
  	 * zero.
--- 1597,1608 ----
  	init_ps_display("stats collector process", "", "");
  	set_ps_display("");
  
  	need_statwrite = TRUE;
  
+ 	MemSet(&timeval, 0, sizeof(struct itimerval));
+ 	timeval.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
+ 	timeval.it_value.tv_usec = PGSTAT_STAT_INTERVAL % 1000;
+ 
  	/*
  	 * Read in an existing statistics stats file or initialize the stats to
  	 * zero.
***************
*** 1634,1667 ****
  	 */
  	for (;;)
  	{
- 		/*
- 		 * If we need to write the status file again (there have been changes
- 		 * in the statistics since we wrote it last) calculate the timeout
- 		 * until we have to do so.
- 		 */
  		if (need_statwrite)
  		{
! 			struct timeval now;
! 
! 			gettimeofday(&now, NULL);
! 			/* avoid assuming that tv_sec is signed */
! 			if (now.tv_sec > next_statwrite.tv_sec ||
! 				(now.tv_sec == next_statwrite.tv_sec &&
! 				 now.tv_usec >= next_statwrite.tv_usec))
! 			{
! 				timeout.tv_sec = 0;
! 				timeout.tv_usec = 0;
! 			}
! 			else
! 			{
! 				timeout.tv_sec = next_statwrite.tv_sec - now.tv_sec;
! 				timeout.tv_usec = next_statwrite.tv_usec - now.tv_usec;
! 				if (timeout.tv_usec < 0)
! 				{
! 					timeout.tv_sec--;
! 					timeout.tv_usec += 1000000;
! 				}
! 			}
  		}
  
  		/*
--- 1634,1644 ----
  	 */
  	for (;;)
  	{
  		if (need_statwrite)
  		{
! 			pgstat_write_statsfile();
! 			need_statwrite = false;
! 			need_timer = true;
  		}
  
  		/*
***************
*** 1673,1681 ****
  		/*
  		 * Now wait for something to do.
  		 */
! 		nready = select(readPipe + 1, &rfds, NULL, NULL,
! 						(need_statwrite) ? &timeout : NULL);
! 		if (nready < 0)
  		{
  			if (errno == EINTR)
  				continue;
--- 1650,1656 ----
  		/*
  		 * Now wait for something to do.
  		 */
! 		if (select(readPipe + 1, &rfds, NULL, NULL, NULL) < 0)
  		{
  			if (errno == EINTR)
  				continue;
***************
*** 1685,1702 ****
  		}
  
  		/*
- 		 * If there are no descriptors ready, our timeout for writing the
- 		 * stats file happened.
- 		 */
- 		if (nready == 0)
- 		{
- 			pgstat_write_statsfile();
- 			need_statwrite = FALSE;
- 
- 			continue;
- 		}
- 
- 		/*
  		 * Check if there is a new statistics message to collect.
  		 */
  		if (FD_ISSET(readPipe, &rfds))
--- 1660,1665 ----
***************
*** 1813,1829 ****
  			 */
  			pgStatNumMessages++;
  
! 			/*
! 			 * If this is the first message after we wrote the stats file the
! 			 * last time, setup the timeout that it'd be written.
! 			 */
! 			if (!need_statwrite)
  			{
! 				gettimeofday(&next_statwrite, NULL);
! 				next_statwrite.tv_usec += ((PGSTAT_STAT_INTERVAL) * 1000);
! 				next_statwrite.tv_sec += (next_statwrite.tv_usec / 1000000);
! 				next_statwrite.tv_usec %= 1000000;
! 				need_statwrite = TRUE;
  			}
  		}
  
--- 1776,1787 ----
  			 */
  			pgStatNumMessages++;
  
! 			if (need_timer)
  			{
! 				if (setitimer(ITIMER_REAL, &timeval, NULL))
! 					ereport(ERROR,
! 						  (errmsg("unable to set statistics collector timer: %m")));
! 				need_timer = false;
  			}
  		}
  
***************
*** 1848,1853 ****
--- 1806,1818 ----
  }
  
  
+ static void
+ force_statwrite(SIGNAL_ARGS)
+ {
+ 	need_statwrite = true;
+ }
+ 
+ 
  /* ----------
   * pgstat_recvbuffer() -
   *

--ELM1136227240-6886-0_--

From pgsql-patches-owner@postgresql.org  Mon Jan  2 14:45:27 2006
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Michael Fuhr <mike@fuhr.org>,
	Merlin Moncure <merlin.moncure@rcsonline.com>,
	Carlos Benkendorf <carlosbenkendorf@yahoo.com.br>,
	PostgreSQL-patches <pgsql-patches@postgresql.org>
Subject: Re: Stats collector performance improvement 
In-reply-to: <200601021840.k02Ieed21704@candle.pha.pa.us> 
References: <200601021840.k02Ieed21704@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Mon, 02 Jan 2006 13:40:40 -0500"
Date: Mon, 02 Jan 2006 13:45:21 -0500
Message-ID: <7838.1136227521@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I found if I put a pg_usleep(100) in the buffer process the backend
> speed was good, but packets were lost.  What I found worked well was to
> do multiple recv() calls in a loop.  The previous code did a select(),
> then perhaps a recv() and pipe write() based on the results of the
> select().  This caused many small packets to be written to the pipe and
> the pipe write overhead seems fairly large.  The best fix I found was to
> loop over the recv() call at most 25 times, collecting a group of
> packets that can then be sent to the collector in one pipe write.  The
> recv() socket is non-blocking, so a zero return indicates there are no
> more packets available.  Patch attached.

This seems incredibly OS-specific.  How many platforms did you test it
on?

A more serious objection is that it will cause the stats machinery to
work very poorly if there isn't a steady stream of incoming messages.
You can't just sit on 24 messages until the 25th one arrives next week.

			regards, tom lane

From pgsql-patches-owner@postgresql.org  Mon Jan  2 15:13:59 2006
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200601021913.k02JDlh26741@candle.pha.pa.us>
Subject: Re: Stats collector performance improvement
In-Reply-To: <7838.1136227521@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 2 Jan 2006 14:13:47 -0500 (EST)
CC: Michael Fuhr <mike@fuhr.org>,
	Merlin Moncure <merlin.moncure@rcsonline.com>,
	Carlos Benkendorf <carlosbenkendorf@yahoo.com.br>,
	PostgreSQL-patches <pgsql-patches@postgresql.org>
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Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I found if I put a pg_usleep(100) in the buffer process the backend
> > speed was good, but packets were lost.  What I found worked well was to
> > do multiple recv() calls in a loop.  The previous code did a select(),
> > then perhaps a recv() and pipe write() based on the results of the
> > select().  This caused many small packets to be written to the pipe and
> > the pipe write overhead seems fairly large.  The best fix I found was to
> > loop over the recv() call at most 25 times, collecting a group of
> > packets that can then be sent to the collector in one pipe write.  The
> > recv() socket is non-blocking, so a zero return indicates there are no
> > more packets available.  Patch attached.
> 
> This seems incredibly OS-specific.  How many platforms did you test it
> on?

Only mine.  I am posting the patch so others can test it, of course.

> A more serious objection is that it will cause the stats machinery to
> work very poorly if there isn't a steady stream of incoming messages.
> You can't just sit on 24 messages until the 25th one arrives next week.

You wouldn't.  It exits out of the loop on a not found, checks the pipe
write descriptor, and writes on it.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-hackers-owner@postgresql.org  Mon Jan  2 16:20:27 2006
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, pgsql-hackers@postgreSQL.org
Subject: Re: Stats collector performance improvement 
In-reply-to: <200601021840.k02Ieed21704@candle.pha.pa.us> 
References: <200601021840.k02Ieed21704@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Mon, 02 Jan 2006 13:40:40 -0500"
Date: Mon, 02 Jan 2006 15:20:24 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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[ moving to -hackers ]

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I did some research on this because the numbers Tom quotes indicate there
> is something wrong in the way we process stats_command_string
> statistics.
> [ ... proposed patch that seems pretty klugy to me ... ]

I wonder whether we shouldn't consider something more drastic, like
getting rid of the intermediate stats buffer process entirely.

The original design for the stats communication code was based on the
premise that it's better to drop data than to make backends wait on
the stats collector.  However, as things have turned out I think this
notion is a flop: the people who are using stats at all want the stats
to be reliable.  We've certainly seen plenty of gripes from people who
are unhappy that backend-exit messages got dropped, and anyone who's
using autovacuum would really like the tuple update counts to be pretty
solid too.

If we abandoned the unreliable-communication approach, could we build
something with less overhead?

			regards, tom lane

From pgsql-hackers-owner@postgresql.org  Mon Jan  2 17:02:14 2006
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"Tom Lane" <tgl@sss.pgh.pa.us> wrote
>
> I wonder whether we shouldn't consider something more drastic, like
> getting rid of the intermediate stats buffer process entirely.
>
> The original design for the stats communication code was based on the
> premise that it's better to drop data than to make backends wait on
> the stats collector.  However, as things have turned out I think this
> notion is a flop: the people who are using stats at all want the stats
> to be reliable.  We've certainly seen plenty of gripes from people who
> are unhappy that backend-exit messages got dropped, and anyone who's
> using autovacuum would really like the tuple update counts to be pretty
> solid too.
>

AFAICS if we can maintain the stats counts solid, then it may hurt 
performance dramatically. Think if we maintain 
pgstat_count_heap_insert()/pgstat_count_heap_delete() pretty well, then we 
get a replacement of count(*). To do so, I believe that will add another 
lock contention on the target table stats.

Regards,
Qingqing 



From pgsql-hackers-owner@postgresql.org  Mon Jan  2 17:48:25 2006
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Subject: Re: Stats collector performance improvement
From: Hannu Krosing <hannu@skype.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
	Jan Wieck <JanWieck@Yahoo.com>, pgsql-hackers@postgreSQL.org
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	<11924.1136233224@sss.pgh.pa.us>
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Ühel kenal päeval, E, 2006-01-02 kell 15:20, kirjutas Tom Lane:
> [ moving to -hackers ]
> 
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I did some research on this because the numbers Tom quotes indicate there
> > is something wrong in the way we process stats_command_string
> > statistics.
> > [ ... proposed patch that seems pretty klugy to me ... ]
> 
> I wonder whether we shouldn't consider something more drastic, like
> getting rid of the intermediate stats buffer process entirely.
> 
> The original design for the stats communication code was based on the
> premise that it's better to drop data than to make backends wait on
> the stats collector.  However, as things have turned out I think this
> notion is a flop: the people who are using stats at all want the stats
> to be reliable.  We've certainly seen plenty of gripes from people who
> are unhappy that backend-exit messages got dropped, and anyone who's
> using autovacuum would really like the tuple update counts to be pretty
> solid too.
> 
> If we abandoned the unreliable-communication approach, could we build
> something with less overhead?

Weell, at least it should be non-WAL, and probably non-fsync, at least
optionally . Maybe also inserts inserts + offline aggregator (instead of
updates) to avoid lock contention. Something that collects data in
blocks of local or per-backend shared memory in each backend and then
gives complete blocks to aggregator process. Maybe use 2 alternating
blocks per backend - 1 for ongoing stats collection and another given to
aggregator. this has a little time shift, but will deliver accurate
starts in the end. Things that need up-to-date stats (like
pg_stat_activity), should look (and lock) also the ongoing satas
collection blocks if needed (how do we know know the *if*) and delay
each backend process momentaryly by looking.

-----------------
Hannu



From pgsql-hackers-owner@postgresql.org  Mon Jan  2 17:48:47 2006
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To: "Qingqing Zhou" <zhouqq@cs.toronto.edu>
cc: pgsql-hackers@postgresql.org
Subject: Re: Stats collector performance improvement 
In-reply-to: <dpc4cg$lm6$1@news.hub.org> 
References: <200601021840.k02Ieed21704@candle.pha.pa.us>
	<11924.1136233224@sss.pgh.pa.us> <dpc4cg$lm6$1@news.hub.org>
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	message dated "Mon, 02 Jan 2006 16:03:20 -0500"
Date: Mon, 02 Jan 2006 16:48:45 -0500
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"Qingqing Zhou" <zhouqq@cs.toronto.edu> writes:
> AFAICS if we can maintain the stats counts solid, then it may hurt 
> performance dramatically. Think if we maintain 
> pgstat_count_heap_insert()/pgstat_count_heap_delete() pretty well, then we 
> get a replacement of count(*).

Not at all.  For one thing, the stats don't attempt to maintain
per-transaction state, so they don't have the MVCC issues of count(*).
I'm not suggesting any fundamental changes in what is counted or when.

The two compromises that were made in the original stats design to make
it fast were (1) stats updates lag behind reality, and (2) some updates
may be missed entirely.  Now that we have a couple of years' field
experience with the code, it seems that (1) is acceptable for real usage
but (2) not so much.  And it's not even clear that we are buying any
performance gain from (2), considering that it's adding the overhead of
passing the data through an extra process.

			regards, tom lane

From pgsql-hackers-owner@postgresql.org  Tue Jan  3 00:07:10 2006
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CC: Bruce Momjian <pgman@candle.pha.pa.us>, pgsql-hackers@postgreSQL.org
Subject: Re: Stats collector performance improvement
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On 1/2/2006 3:20 PM, Tom Lane wrote:

> [ moving to -hackers ]
> 
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> I did some research on this because the numbers Tom quotes indicate there
>> is something wrong in the way we process stats_command_string
>> statistics.
>> [ ... proposed patch that seems pretty klugy to me ... ]
> 
> I wonder whether we shouldn't consider something more drastic, like
> getting rid of the intermediate stats buffer process entirely.
> 
> The original design for the stats communication code was based on the
> premise that it's better to drop data than to make backends wait on

The original design was geared towards searching for useless/missing 
indexes and tuning activity like that. This never happened, but instead 
people tried to use it as a reliable debugging or access statistics aid 
... which is fine but not what it originally was intended for.

So yes, I think looking at what it usually is used for, a message 
passing system like SysV message queues (puke) or similar would do a 
better job.


Jan

> the stats collector.  However, as things have turned out I think this
> notion is a flop: the people who are using stats at all want the stats
> to be reliable.  We've certainly seen plenty of gripes from people who
> are unhappy that backend-exit messages got dropped, and anyone who's
> using autovacuum would really like the tuple update counts to be pretty
> solid too.
> 
> If we abandoned the unreliable-communication approach, could we build
> something with less overhead?
> 
> 			regards, tom lane


-- 
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#================================================== JanWieck@Yahoo.com #

From pgsql-hackers-owner@postgresql.org  Tue Jan  3 05:40:59 2006
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Subject: Re: Stats collector performance improvement
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Qingqing Zhou <zhouqq@cs.toronto.edu>,
	pgsql-hackers@postgresql.org
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On Mon, 2006-01-02 at 16:48 -0500, Tom Lane wrote:

> The two compromises that were made in the original stats design to make
> it fast were (1) stats updates lag behind reality, and (2) some updates
> may be missed entirely.  Now that we have a couple of years' field
> experience with the code, it seems that (1) is acceptable for real usage
> but (2) not so much. 

We decided that the stats update had to occur during execution, in case
the statement aborted and row versions were not notified. That means we
must notify things as they happen, yet could use a reliable queuing
system that could suffer a delay in the stats becoming available.

But how often do we lose a backend? Could we simply buffer that a little
better? i.e. don't send message to stats unless we have altered at least
10 rows? So we would buffer based upon the importance of the message,
not the actual size of the message. That way singleton-statements won't
generate the same stats traffic, but we risk losing a buffers worth of
row changes should we crash - everything would still work if we lost a
few small row change notifications.

We can also save lots of cycles on the current statement overhead, which
is currently the worst part of the stats, performance-wise. That
definitely needs redesign. AFAICS we only ever need to know the SQL
statement via the stats system if the statement has been running for
more than a few minutes - the main use case is for an admin to be able
to diagnose a rogue or hung statement. Pushing the statement to stats
every time is just a big overhead. That suggests we should either have a
pull or a deferred push (longer-than-X-secs) approach.

Best Regards, Simon Riggs


From pgsql-patches-owner@postgresql.org  Tue Jan  3 05:54:58 2006
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Subject: Re: Stats collector performance improvement
From: Simon Riggs <simon@2ndquadrant.com>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Michael Fuhr <mike@fuhr.org>,
	Merlin Moncure <merlin.moncure@rcsonline.com>,
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On Mon, 2006-01-02 at 13:40 -0500, Bruce Momjian wrote:

> This change reduced the stats_command_string time from 5.5 to 3.9, which
> is closer to the 3.5 seconds with stats_command_string off.

Excellent work, port specific or not.

Best Regards, Simon Riggs


From pgsql-performance-owner@postgresql.org  Tue Jan  3 11:08:52 2006
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Date: Tue, 03 Jan 2006 16:08:48 +0100
From: Jens-Wolfhard Schicke <ml+pgsql-performance@asco.de>
Reply-To: Jens-Wolfhard Schicke <j.schicke@asco.de>
To: pgsql-performance@postgresql.org
Subject: Materialize Subplan and push into inner index conditions
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Is it possible to have the planner consider the second plan instead of the=20
first?

admpostgres4=3D> explain analyze select * from users where id in (select=20
user_id from user2user_group where user_group_id =3D 769694);
=20
QUERY PLAN=20

----------------------------------------------------------------------------=
----------------------------------------------------------------------------=
-------
 Hash IN Join  (cost=3D4.04..2302.05 rows=3D4 width=3D78) (actual=20
time=3D50.381..200.985 rows=3D2 loops=3D1)
   Hash Cond: ("outer".id =3D "inner".user_id)
   ->  Append  (cost=3D0.00..1931.68 rows=3D77568 width=3D78) (actual=20
time=3D0.004..154.629 rows=3D76413 loops=3D1)
         ->  Seq Scan on users  (cost=3D0.00..1024.88 rows=3D44588 =
width=3D78)=20
(actual time=3D0.004..36.220 rows=3D43433 loops=3D1)
         ->  Seq Scan on person_user users  (cost=3D0.00..906.80 =
rows=3D32980=20
width=3D78) (actual time=3D0.005..38.120 rows=3D32980 loops=3D1)
   ->  Hash  (cost=3D4.04..4.04 rows=3D2 width=3D4) (actual =
time=3D0.020..0.020=20
rows=3D2 loops=3D1)
         ->  Index Scan using user2user_group_user_group_id_idx on=20
user2user_group  (cost=3D0.00..4.04 rows=3D2 width=3D4) (actual =
time=3D0.011..0.014=20
rows=3D2 loops=3D1)
               Index Cond: (user_group_id =3D 769694)
 Total runtime: 201.070 ms
(9 rows)

admpostgres4=3D> select user_id from user2user_group where user_group_id =
=3D=20
769694;
 user_id
---------
  766541
  766552
(2 rows)

admpostgres4=3D> explain analyze select * from users where id in (766541,=20
766552);
                                                                 QUERY PLAN =


----------------------------------------------------------------------------=
-----------------------------------------------------------------
 Result  (cost=3D4.02..33.48 rows=3D9 width=3D78) (actual =
time=3D0.055..0.087=20
rows=3D2 loops=3D1)
   ->  Append  (cost=3D4.02..33.48 rows=3D9 width=3D78) (actual =
time=3D0.051..0.082=20
rows=3D2 loops=3D1)
         ->  Bitmap Heap Scan on users  (cost=3D4.02..18.10 rows=3D5 =
width=3D78)=20
(actual time=3D0.051..0.053 rows=3D2 loops=3D1)
               Recheck Cond: ((id =3D 766541) OR (id =3D 766552))
               ->  BitmapOr  (cost=3D4.02..4.02 rows=3D5 width=3D0) (actual =

time=3D0.045..0.045 rows=3D0 loops=3D1)
                     ->  Bitmap Index Scan on users_id_idx=20
(cost=3D0.00..2.01 rows=3D2 width=3D0) (actual time=3D0.034..0.034 rows=3D1 =
loops=3D1)
                           Index Cond: (id =3D 766541)
                     ->  Bitmap Index Scan on users_id_idx=20
(cost=3D0.00..2.01 rows=3D2 width=3D0) (actual time=3D0.008..0.008 rows=3D1 =
loops=3D1)
                           Index Cond: (id =3D 766552)
         ->  Bitmap Heap Scan on person_user users  (cost=3D4.02..15.37=20
rows=3D4 width=3D78) (actual time=3D0.025..0.025 rows=3D0 loops=3D1)
               Recheck Cond: ((id =3D 766541) OR (id =3D 766552))
               ->  BitmapOr  (cost=3D4.02..4.02 rows=3D4 width=3D0) (actual =

time=3D0.023..0.023 rows=3D0 loops=3D1)
                     ->  Bitmap Index Scan on person_user_id_idx=20
(cost=3D0.00..2.01 rows=3D2 width=3D0) (actual time=3D0.017..0.017 rows=3D0 =
loops=3D1)
                           Index Cond: (id =3D 766541)
                     ->  Bitmap Index Scan on person_user_id_idx=20
(cost=3D0.00..2.01 rows=3D2 width=3D0) (actual time=3D0.004..0.004 rows=3D0 =
loops=3D1)
                           Index Cond: (id =3D 766552)
 Total runtime: 0.177 ms
(17 rows)

admpostgres4=3D>

admpostgres4=3D> \d users;
                          Table "adm.users"
      Column      |            Type             |      Modifiers
------------------+-----------------------------+---------------------
 id               | integer                     | not null
 classid          | integer                     | not null
 revision         | integer                     | not null
 rev_start        | timestamp without time zone |
 rev_end          | timestamp without time zone |
 rev_timestamp    | timestamp without time zone | not null
 rev_state        | integer                     | not null default 10
 name             | character varying           |
 password         | character varying           |
 password_expires | timestamp without time zone |
 password_period  | integer                     |
Indexes:
    "users_pkey" primary key, btree (revision)
    "users_uidx" unique, btree (revision)
    "users_id_idx" btree (id)
    "users_name_idx" btree (rev_state, rev_end, name)
    "users_rev_end_idx" btree (rev_end)
    "users_rev_idx" btree (rev_state, rev_end)
    "users_rev_start_idx" btree (rev_start)
    "users_rev_state_idx" btree (rev_state)
Inherits: revision

admpostgres4=3D>\d person_user;
                       Table "adm.person_user"
      Column      |            Type             |      Modifiers
------------------+-----------------------------+---------------------
 id               | integer                     | not null
 classid          | integer                     | not null
 revision         | integer                     | not null
 rev_start        | timestamp without time zone |
 rev_end          | timestamp without time zone |
 rev_timestamp    | timestamp without time zone | not null
 rev_state        | integer                     | not null default 10
 name             | character varying           |
 password         | character varying           |
 password_expires | timestamp without time zone |
 password_period  | integer                     |
 lastname         | character varying           |
 description      | character varying           |
 vat_id           | character varying           |
 firstname        | character varying           |
 sex              | integer                     |
 birthdate        | timestamp without time zone |
 title            | character varying           |
Indexes:
    "person_user_pkey" primary key, btree (revision)
    "person_user_uidx" unique, btree (revision)
    "person_user_id_idx" btree (id)
    "person_user_rev_end_idx" btree (rev_end)
    "person_user_rev_idx" btree (rev_state, rev_end)
    "person_user_rev_start_idx" btree (rev_start)
    "person_user_rev_state_idx" btree (rev_state)
Inherits: users

admpostgres4=3D>

admpostgres4=3D> \d user2user_group;
     Table "adm.user2user_group"
    Column     |  Type   | Modifiers
---------------+---------+-----------
 user_id       | integer | not null
 user_group_id | integer | not null
Indexes:
    "user2user_group_pkey" primary key, btree (user_id, user_group_id)
    "user2user_group_uidx" unique, btree (user_id, user_group_id)
    "user2user_group_user_group_id_idx" btree (user_group_id)
    "user2user_group_user_id_idx" btree (user_id)

admpostgres4=3D>

Mit freundlichem Gru=DF
Jens Schicke
--=20
Jens Schicke		      j.schicke@asco.de
asco GmbH		      http://www.asco.de
Mittelweg 7		      Tel 0531/3906-127
38106 Braunschweig	      Fax 0531/3906-400

From pgsql-performance-owner@postgresql.org  Tue Jan  3 11:43:36 2006
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To: Jens-Wolfhard Schicke <j.schicke@asco.de>
cc: pgsql-performance@postgresql.org
Subject: Re: Materialize Subplan and push into inner index conditions 
In-reply-to: <B83CC5FD82571D5D9439CE4C@[192.168.1.72]> 
References: <B83CC5FD82571D5D9439CE4C@[192.168.1.72]>
Comments: In-reply-to Jens-Wolfhard Schicke <ml+pgsql-performance@asco.de>
	message dated "Tue, 03 Jan 2006 16:08:48 +0100"
Date: Tue, 03 Jan 2006 10:43:34 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Jens-Wolfhard Schicke <ml+pgsql-performance@asco.de> writes:
> Is it possible to have the planner consider the second plan instead of the 
> first?

At the moment, only if you get rid of the inheritance.  The planner's
not very smart at all when faced with joining inheritance trees.

			regards, tom lane

From pgsql-hackers-owner@postgresql.org  Tue Jan  3 12:35:58 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Qingqing Zhou <zhouqq@cs.toronto.edu>,
	pgsql-hackers@postgresql.org
Subject: Re: Stats collector performance improvement
Message-ID: <20060103163556.GH82560@pervasive.com>
References: <200601021840.k02Ieed21704@candle.pha.pa.us>
	<11924.1136233224@sss.pgh.pa.us> <dpc4cg$lm6$1@news.hub.org>
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On Tue, Jan 03, 2006 at 09:40:53AM +0000, Simon Riggs wrote:
> On Mon, 2006-01-02 at 16:48 -0500, Tom Lane wrote:
> We can also save lots of cycles on the current statement overhead, which
> is currently the worst part of the stats, performance-wise. That
> definitely needs redesign. AFAICS we only ever need to know the SQL
> statement via the stats system if the statement has been running for
> more than a few minutes - the main use case is for an admin to be able
> to diagnose a rogue or hung statement. Pushing the statement to stats
> every time is just a big overhead. That suggests we should either have a
> pull or a deferred push (longer-than-X-secs) approach.

I would argue that minutes is too long, but of course this could be
user-adjustable. I suspect that even waiting just a second could be a
huge win, since this only matters if you're executing a lot of
statements and you won't be doing that if those statements are taking
more than a second or two to execute.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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Subject: Re: Stats collector performance improvement
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Date: Tue, 3 Jan 2006 11:43:23 -0500 (EST)
CC: Tom Lane <tgl@sss.pgh.pa.us>, Michael Fuhr <mike@fuhr.org>,
	Merlin Moncure <merlin.moncure@rcsonline.com>,
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Bruce Momjian wrote:
> Tom Lane wrote:
> A second improvement I discovered is that the statistics collector is
> calling gettimeofday() for every packet received, so it can determine
> the timeout for the select() call to write the flat file.  I removed
> that behavior and instead used setitimer() to issue a SIGINT every
> 500ms, which was the original behavior.  This eliminates the
> gettimeofday() call and makes the code cleaner.  Second patch attached.

I have applied this second patch, with a few small stylistic
improvements.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

--ELM1136306603-6886-1_
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Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.116
diff -c -c -r1.116 pgstat.c
*** src/backend/postmaster/pgstat.c	2 Jan 2006 00:58:00 -0000	1.116
--- src/backend/postmaster/pgstat.c	3 Jan 2006 16:26:04 -0000
***************
*** 117,123 ****
  
  static long pgStatNumMessages = 0;
  
! static bool pgStatRunningInCollector = FALSE;
  
  /*
   * Place where backends store per-table info to be sent to the collector.
--- 117,123 ----
  
  static long pgStatNumMessages = 0;
  
! static bool pgStatRunningInCollector = false;
  
  /*
   * Place where backends store per-table info to be sent to the collector.
***************
*** 145,150 ****
--- 145,151 ----
  static PgStat_StatBeEntry *pgStatBeTable = NULL;
  static int	pgStatNumBackends = 0;
  
+ static volatile bool	need_statwrite;
  
  /* ----------
   * Local function forward declarations
***************
*** 164,169 ****
--- 165,171 ----
  
  NON_EXEC_STATIC void PgstatBufferMain(int argc, char *argv[]);
  NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]);
+ static void force_statwrite(SIGNAL_ARGS);
  static void pgstat_recvbuffer(void);
  static void pgstat_exit(SIGNAL_ARGS);
  static void pgstat_die(SIGNAL_ARGS);
***************
*** 1548,1560 ****
  	PgStat_Msg	msg;
  	fd_set		rfds;
  	int			readPipe;
- 	int			nready;
  	int			len = 0;
! 	struct timeval timeout;
! 	struct timeval next_statwrite;
! 	bool		need_statwrite;
  	HASHCTL		hash_ctl;
! 
  	MyProcPid = getpid();		/* reset MyProcPid */
  
  	/*
--- 1550,1560 ----
  	PgStat_Msg	msg;
  	fd_set		rfds;
  	int			readPipe;
  	int			len = 0;
! 	struct itimerval timeval;
  	HASHCTL		hash_ctl;
! 	bool		need_timer = false;
! 	
  	MyProcPid = getpid();		/* reset MyProcPid */
  
  	/*
***************
*** 1572,1578 ****
  	/* kluge to allow buffer process to kill collector; FIXME */
  	pqsignal(SIGQUIT, pgstat_exit);
  #endif
! 	pqsignal(SIGALRM, SIG_IGN);
  	pqsignal(SIGPIPE, SIG_IGN);
  	pqsignal(SIGUSR1, SIG_IGN);
  	pqsignal(SIGUSR2, SIG_IGN);
--- 1572,1578 ----
  	/* kluge to allow buffer process to kill collector; FIXME */
  	pqsignal(SIGQUIT, pgstat_exit);
  #endif
! 	pqsignal(SIGALRM, force_statwrite);
  	pqsignal(SIGPIPE, SIG_IGN);
  	pqsignal(SIGUSR1, SIG_IGN);
  	pqsignal(SIGUSR2, SIG_IGN);
***************
*** 1597,1613 ****
  	init_ps_display("stats collector process", "", "");
  	set_ps_display("");
  
! 	/*
! 	 * Arrange to write the initial status file right away
! 	 */
! 	gettimeofday(&next_statwrite, NULL);
! 	need_statwrite = TRUE;
  
  	/*
  	 * Read in an existing statistics stats file or initialize the stats to
  	 * zero.
  	 */
! 	pgStatRunningInCollector = TRUE;
  	pgstat_read_statsfile(&pgStatDBHash, InvalidOid, NULL, NULL);
  
  	/*
--- 1597,1613 ----
  	init_ps_display("stats collector process", "", "");
  	set_ps_display("");
  
! 	need_statwrite = true;
! 
! 	MemSet(&timeval, 0, sizeof(struct itimerval));
! 	timeval.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
! 	timeval.it_value.tv_usec = PGSTAT_STAT_INTERVAL % 1000;
  
  	/*
  	 * Read in an existing statistics stats file or initialize the stats to
  	 * zero.
  	 */
! 	pgStatRunningInCollector = true;
  	pgstat_read_statsfile(&pgStatDBHash, InvalidOid, NULL, NULL);
  
  	/*
***************
*** 1634,1667 ****
  	 */
  	for (;;)
  	{
- 		/*
- 		 * If we need to write the status file again (there have been changes
- 		 * in the statistics since we wrote it last) calculate the timeout
- 		 * until we have to do so.
- 		 */
  		if (need_statwrite)
  		{
! 			struct timeval now;
! 
! 			gettimeofday(&now, NULL);
! 			/* avoid assuming that tv_sec is signed */
! 			if (now.tv_sec > next_statwrite.tv_sec ||
! 				(now.tv_sec == next_statwrite.tv_sec &&
! 				 now.tv_usec >= next_statwrite.tv_usec))
! 			{
! 				timeout.tv_sec = 0;
! 				timeout.tv_usec = 0;
! 			}
! 			else
! 			{
! 				timeout.tv_sec = next_statwrite.tv_sec - now.tv_sec;
! 				timeout.tv_usec = next_statwrite.tv_usec - now.tv_usec;
! 				if (timeout.tv_usec < 0)
! 				{
! 					timeout.tv_sec--;
! 					timeout.tv_usec += 1000000;
! 				}
! 			}
  		}
  
  		/*
--- 1634,1644 ----
  	 */
  	for (;;)
  	{
  		if (need_statwrite)
  		{
! 			pgstat_write_statsfile();
! 			need_statwrite = false;
! 			need_timer = true;
  		}
  
  		/*
***************
*** 1673,1681 ****
  		/*
  		 * Now wait for something to do.
  		 */
! 		nready = select(readPipe + 1, &rfds, NULL, NULL,
! 						(need_statwrite) ? &timeout : NULL);
! 		if (nready < 0)
  		{
  			if (errno == EINTR)
  				continue;
--- 1650,1656 ----
  		/*
  		 * Now wait for something to do.
  		 */
! 		if (select(readPipe + 1, &rfds, NULL, NULL, NULL) < 0)
  		{
  			if (errno == EINTR)
  				continue;
***************
*** 1685,1702 ****
  		}
  
  		/*
- 		 * If there are no descriptors ready, our timeout for writing the
- 		 * stats file happened.
- 		 */
- 		if (nready == 0)
- 		{
- 			pgstat_write_statsfile();
- 			need_statwrite = FALSE;
- 
- 			continue;
- 		}
- 
- 		/*
  		 * Check if there is a new statistics message to collect.
  		 */
  		if (FD_ISSET(readPipe, &rfds))
--- 1660,1665 ----
***************
*** 1813,1829 ****
  			 */
  			pgStatNumMessages++;
  
! 			/*
! 			 * If this is the first message after we wrote the stats file the
! 			 * last time, setup the timeout that it'd be written.
! 			 */
! 			if (!need_statwrite)
  			{
! 				gettimeofday(&next_statwrite, NULL);
! 				next_statwrite.tv_usec += ((PGSTAT_STAT_INTERVAL) * 1000);
! 				next_statwrite.tv_sec += (next_statwrite.tv_usec / 1000000);
! 				next_statwrite.tv_usec %= 1000000;
! 				need_statwrite = TRUE;
  			}
  		}
  
--- 1776,1787 ----
  			 */
  			pgStatNumMessages++;
  
! 			if (need_timer)
  			{
! 				if (setitimer(ITIMER_REAL, &timeval, NULL))
! 					ereport(ERROR,
! 						  (errmsg("unable to set statistics collector timer: %m")));
! 				need_timer = false;
  			}
  		}
  
***************
*** 1848,1853 ****
--- 1806,1818 ----
  }
  
  
+ static void
+ force_statwrite(SIGNAL_ARGS)
+ {
+ 	need_statwrite = true;
+ }
+ 
+ 
  /* ----------
   * pgstat_recvbuffer() -
   *
***************
*** 1865,1871 ****
  	struct timeval timeout;
  	int			writePipe = pgStatPipe[1];
  	int			maxfd;
- 	int			nready;
  	int			len;
  	int			xfr;
  	int			frm;
--- 1830,1835 ----
***************
*** 1907,1912 ****
--- 1871,1884 ----
  	msgbuffer = (char *) palloc(PGSTAT_RECVBUFFERSZ);
  
  	/*
+ 	 * Wait for some work to do; but not for more than 10 seconds. (This
+ 	 * determines how quickly we will shut down after an ungraceful
+ 	 * postmaster termination; so it needn't be very fast.)
+ 	 */
+ 	timeout.tv_sec = 10;
+ 	timeout.tv_usec = 0;
+ 
+ 	/*
  	 * Loop forever
  	 */
  	for (;;)
***************
*** 1946,1961 ****
  				maxfd = writePipe;
  		}
  
! 		/*
! 		 * Wait for some work to do; but not for more than 10 seconds. (This
! 		 * determines how quickly we will shut down after an ungraceful
! 		 * postmaster termination; so it needn't be very fast.)
! 		 */
! 		timeout.tv_sec = 10;
! 		timeout.tv_usec = 0;
! 
! 		nready = select(maxfd + 1, &rfds, &wfds, NULL, &timeout);
! 		if (nready < 0)
  		{
  			if (errno == EINTR)
  				continue;
--- 1918,1924 ----
  				maxfd = writePipe;
  		}
  
! 		if (select(maxfd + 1, &rfds, &wfds, NULL, &timeout) < 0)
  		{
  			if (errno == EINTR)
  				continue;

--ELM1136306603-6886-1_--

From pgsql-hackers-owner@postgresql.org  Sun Jan  8 08:18:06 2006
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Subject: Re: Stats collector performance improvement
From: Hannu Krosing <hannu@skype.net>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Qingqing Zhou <zhouqq@cs.toronto.edu>, pgsql-hackers@postgresql.org
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Ühel kenal päeval, T, 2006-01-03 kell 09:40, kirjutas Simon Riggs:

> We can also save lots of cycles on the current statement overhead, which
> is currently the worst part of the stats, performance-wise. That
> definitely needs redesign. AFAICS we only ever need to know the SQL
> statement via the stats system if the statement has been running for
> more than a few minutes - the main use case is for an admin to be able
> to diagnose a rogue or hung statement. 

Interestingly I use pg_stat_activity view to watch for stuck backends,
"stuck" in the sense that they have not noticed when client want away
and are now waitin the TCP timeout to happen. I query for backends which
have been in "<IDLE>" state for longer than XX seconds. I guess that at
least some kind of indication for this should be available.

Of course this would be much less of a problem if there was a
possibility for sime kind of keepalive system to detect when
client/frontend goes away.

> Pushing the statement to stats
> every time is just a big overhead. That suggests we should either have a
> pull 

I could live with "push", where pg_stat_activity would actually ask each
live backend for its "current query". This surely happens less often
than queries are performed (up to few thousand per sec)

-------------
Hannu



From pgsql-hackers-owner@postgresql.org  Tue Jan  3 19:28:45 2006
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	Qingqing Zhou <zhouqq@cs.toronto.edu>,  pgsql-hackers@postgresql.org
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"Jim C. Nasby" <jnasby@pervasive.com> writes:

> I would argue that minutes is too long, but of course this could be
> user-adjustable. I suspect that even waiting just a second could be a
> huge win, since this only matters if you're executing a lot of
> statements and you won't be doing that if those statements are taking
> more than a second or two to execute.

That's not necessarily true at all. You could just as easily have a
performance problem caused by a quick statement that is being executed many
times as a slow statement that is being executed few times.

That is, you could be executing dozens of queries that take seconds or minutes
once a second but none of those might be the problem. The problem might be the
query that's taking only 300ms that you're executing hundreds of of times a
minute.

Moreover, if you're not gathering stats for queries that are fast then how
will you know whether they're performing properly when you look at them when
they do show up?

-- 
greg


From pgsql-performance-owner@postgresql.org  Tue Jan  3 19:49:35 2006
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Date: Tue, 03 Jan 2006 16:44:28 -0700
From: Steve Eckmann <eckmann@computer.org>
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Subject: improving write performance for logging application
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I have questions about how to improve the write performance of PostgreSQL for logging data from a real-time simulation. We found that MySQL 4.1.3 could log about 1480 objects/second using MyISAM tables or about 1225 objects/second using InnoDB tables, but PostgreSQL 8.0.3 could log only about 540 objects/second. (test system: quad-Itanium2, 8GB memory, SCSI RAID, GigE connection from simulation server, nothing running except system processes and database system under test)

We also found that we could improve MySQL performance significantly using MySQL's "INSERT" command extension allowing multiple value-list tuples in a single command; the rate for MyISAM tables improved to about 2600 objects/second. PostgreSQL doesn't support that language extension. Using the COPY command instead of INSERT might help, but since rows are being generated on the fly, I don't see how to use COPY without running a separate process that reads rows from the application and uses COPY to write to the database. The application currently has two processes: the simulation and a data collector that reads events from the sim (queued in shared memory) and writes them as rows to the database, buffering as needed to avoid lost data during periods of high activity. To use COPY I think we would have to split our data collector into two processes communicating via a pipe.

Query performance is not an issue: we found that when suitable indexes are added PostgreSQL is fast enough on the kinds of queries our users make. The crux is writing rows to the database fast enough to keep up with the simulation.

Are there general guidelines for tuning the PostgreSQL server for this kind of application? The suggestions I've found include disabling fsync (done), increasing the value of wal_buffers, and moving the WAL to a different disk, but these aren't likely to produce the 3x improvement that we need. On the client side I've found only two suggestions: disable autocommit and use COPY instead of INSERT. I think I've effectively disabled autocommit by batching up to several hundred INSERT commands in each PQexec() call, and it isn�t clear that COPY is worth the effort in our application.

Thanks.


From pgsql-performance-owner@postgresql.org  Tue Jan  3 20:00:13 2006
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To: Steve Eckmann <eckmann@computer.org>
cc: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application 
In-reply-to: <43BB0C5C.8020207@computer.org> 
References: <43BB0C5C.8020207@computer.org>
Comments: In-reply-to Steve Eckmann <eckmann@computer.org>
	message dated "Tue, 03 Jan 2006 16:44:28 -0700"
Date: Tue, 03 Jan 2006 19:00:12 -0500
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Steve Eckmann <eckmann@computer.org> writes:
> We also found that we could improve MySQL performance significantly
> using MySQL's "INSERT" command extension allowing multiple value-list
> tuples in a single command; the rate for MyISAM tables improved to
> about 2600 objects/second. PostgreSQL doesn't support that language
> extension. Using the COPY command instead of INSERT might help, but
> since rows are being generated on the fly, I don't see how to use COPY
> without running a separate process that reads rows from the
> application and uses COPY to write to the database.

Can you conveniently alter your application to batch INSERT commands
into transactions?  Ie

	BEGIN;
	INSERT ...;
	... maybe 100 or so inserts ...
	COMMIT;
	BEGIN;
	... lather, rinse, repeat ...

This cuts down the transactional overhead quite a bit.  A downside is
that you lose multiple rows if any INSERT fails, but then the same would
be true of multiple VALUES lists per INSERT.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan  3 20:06:02 2006
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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: Steve Eckmann <eckmann@computer.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application
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On Tue, Jan 03, 2006 at 04:44:28PM -0700, Steve Eckmann wrote:
> Are there general guidelines for tuning the PostgreSQL server for this kind 
> of application? The suggestions I've found include disabling fsync (done),

Are you sure you really want this? The results could be catastrophic in case
of a crash.

> On the client side I've found only two suggestions: disable autocommit and 
> use COPY instead of INSERT. I think I've effectively disabled autocommit by 
> batching up to several hundred INSERT commands in each PQexec() call, and 
> it isn’t clear that COPY is worth the effort in our application.

I'm a bit confused here: How can you batch multiple INSERTs into large
statements for MySQL, but not batch multiple INSERTs into COPY statements for
PostgreSQL?

Anyhow, putting it all inside one transaction (or a few) is likely to help
quite a lot, but of course less when you have fsync=false. Bunding multiple
statements in each PQexec() call won't really give you that; you'll have to
tell the database so explicitly.

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Tue Jan  3 20:13:58 2006
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Date: Tue, 3 Jan 2006 19:23:23 -0800 (PST)
From: dlang <dlang@invendra.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Steve Eckmann <eckmann@computer.org>,
	<pgsql-performance@postgresql.org>
Subject: Re: improving write performance for logging application
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On Tue, 3 Jan 2006, Tom Lane wrote:

> Steve Eckmann <eckmann@computer.org> writes:
> > We also found that we could improve MySQL performance significantly
> > using MySQL's "INSERT" command extension allowing multiple value-list
> > tuples in a single command; the rate for MyISAM tables improved to
> > about 2600 objects/second. PostgreSQL doesn't support that language
> > extension. Using the COPY command instead of INSERT might help, but
> > since rows are being generated on the fly, I don't see how to use COPY
> > without running a separate process that reads rows from the
> > application and uses COPY to write to the database.
>
> Can you conveniently alter your application to batch INSERT commands
> into transactions?  Ie
>
> 	BEGIN;
> 	INSERT ...;
> 	... maybe 100 or so inserts ...
> 	COMMIT;
> 	BEGIN;
> 	... lather, rinse, repeat ...
>
> This cuts down the transactional overhead quite a bit.  A downside is
> that you lose multiple rows if any INSERT fails, but then the same would
> be true of multiple VALUES lists per INSERT.

Steve, you mentioned that you data collector buffers the data before
sending it to the database, modify it so that each time it goes to send
things to the database you send all the data that's in the buffer as a
single transaction.

I am working on useing postgres to deal with log data and wrote a simple
perl script that read in the log files a line at a time, and then wrote
them 1000 at a time to the database. On a dual Opteron 240 box with 2G of
ram 1x 15krpm SCSI drive (and a untuned postgress install with the compile
time defaults) I was getting 5000-8000 lines/sec (I think this was with
fsync disabled, but I don't remember for sure). and postgres was
complaining that it was overrunning it's log sizes (which limits the speed
as it then has to pause to flush the logs)

the key thing is to send multiple lines with one transaction as tom shows
above.

David Lang


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Subject: Avoiding cartesian product
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I have a table which stores cumulative values
I would like to display/chart the deltas between successive data =
collections

If my primary key only increments by 1, I could write a simple query

select b.gc_minor - a.gc_minor, b.gc_major - a.gc_major
  from jam_trace_sys a, jam_trace_sys b
 where a.trace_id =3D 22
   and b.trace_id =3D a.trace_id
   and b.seq_no =3D a.seq_no + 1
 order by a.seq_no;

However the difference in sequence number is variable.
So (in Oracle) I used to extract the next seq_no using a correlated =
sub-query

select b.gc_minor - a.gc_minor, b.gc_major - a.gc_major
from jam_trace_sys a, jam_trace_sys b
where a.trace_id =3D 22
and (b.trace_id, b.seq_no) =3D
(select a.trace_id, min(c.seq_no) from jam_trace_sys c
where c.trace_id =3D a.trace_id and c.seq_no > a.seq_no)
 order by a.seq_no;

For every row in A, The correlated sub-query from C will execute
With an appropriate index, it will just descend the index Btree
go one row to the right and return that row (min > :value)
and join to table B

SELECT STATEMENT
  SORT ORDER BY
   TABLE ACCESS BY INDEX ROWID JAM_TRACE_SYS B
     NESTED LOOPS
       TABLE ACCESS BY INDEX ROWID JAM_TRACE_SYS  A
         INDEX RANGE SCAN JAM_TRACE_SYS_N1  A
       INDEX RANGE SCAN JAM_TRACE_SYS_N1 B
         SORT AGGREGATE
           INDEX RANGE SCAN JAM_TRACE_SYS_N1 C

In postgreSQL A and B are doing a cartesian product
then C gets executed for every row in this cartesian product
and most of the extra rows get thrown out.
Is there any way to force an execution plan like above where the =
correlated subquery runs before going to B.
The table is small right now, but it will grow to have millions of rows

QUERY PLAN
-------------------------------------------------------------------------=
----------------------------------------------------------
 Sort  (cost=3D124911.81..124944.84 rows=3D13213 width=3D20) (actual =
time=3D13096.754..13097.053 rows=3D149 loops=3D1)
   Sort Key: a.seq_no
   ->  Nested Loop  (cost=3D4.34..124007.40 rows=3D13213 width=3D20) =
(actual time=3D1948.300..13096.329 rows=3D149 loops=3D1)
         Join Filter: (subplan)
         ->  Seq Scan on jam_trace_sys b  (cost=3D0.00..3.75 rows=3D175 =
width=3D16) (actual time=3D0.005..0.534 rows=3D175 loops=3D1)
         ->  Materialize  (cost=3D4.34..5.85 rows=3D151 width=3D16) =
(actual time=3D0.002..0.324 rows=3D150 loops=3D175)
               ->  Seq Scan on jam_trace_sys a  (cost=3D0.00..4.19 =
rows=3D151 width=3D16) (actual time=3D0.022..0.687 rows=3D150 loops=3D1)
                     Filter: (trace_id =3D 22)
         SubPlan
           ->  Aggregate  (cost=3D4.67..4.67 rows=3D1 width=3D4) (actual =
time=3D0.486..0.488 rows=3D1 loops=3D26250)
                 ->  Seq Scan on jam_trace_sys c  (cost=3D0.00..4.62 =
rows=3D15 width=3D4) (actual time=3D0.058..0.311 rows=3D74 =
loops=3D26250)
                       Filter: ((trace_id =3D $0) AND (seq_no > $1))
 Total runtime: 13097.557 ms
(13 rows)

pglnx01=3D> \d jam_trace_sys
     Table "public.jam_trace_sys"
     Column      |  Type   | Modifiers
-----------------+---------+-----------
 trace_id        | integer |
 seq_no          | integer |
 cpu_utilization | integer |
 gc_minor        | integer |
 gc_major        | integer |
 heap_used       | integer |
Indexes:
    "jam_trace_sys_n1" btree (trace_id, seq_no)

pglnx01=3D> select count(*) from jam_trace_Sys ;
 count
-------
   175
(1 row)

pglnx01=3D> select trace_id, count(*) from jam_trace_sys group by =
trace_id ;
 trace_id | count
----------+-------
       15 |     2
       18 |    21
       22 |   150
       16 |     2
(4 rows)


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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
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<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>I have a table which stores cumulative =
values<BR>I=20
would like to display/chart the deltas between successive data=20
collections</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>If my primary key only increments by 1, =
I could=20
write a simple query</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>select b.gc_minor - a.gc_minor, =
b.gc_major -=20
a.gc_major<BR>&nbsp; from jam_trace_sys a, jam_trace_sys =
b<BR>&nbsp;where=20
a.trace_id =3D 22<BR>&nbsp;&nbsp; and b.trace_id =3D =
a.trace_id<BR>&nbsp;&nbsp; and=20
b.seq_no =3D a.seq_no + 1<BR>&nbsp;order by a.seq_no;</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>However the difference in sequence =
number is=20
variable.<BR>So (in Oracle) I used to extract the next seq_no using a =
correlated=20
sub-query</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>select b.gc_minor - a.gc_minor, =
b.gc_major -=20
a.gc_major<BR>from jam_trace_sys a, jam_trace_sys b<BR>where a.trace_id =
=3D=20
22<BR>and (b.trace_id, b.seq_no) =3D<BR>(select a.trace_id, =
min(c.seq_no) from=20
jam_trace_sys c<BR>where c.trace_id =3D a.trace_id and c.seq_no &gt;=20
a.seq_no)<BR>&nbsp;order by a.seq_no;</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>For every row in A, The correlated =
sub-query from C=20
will execute<BR>With an appropriate index, it will just descend the =
index=20
Btree<BR>go one row to the right and return that row (min &gt; =
:value)<BR>and=20
join to table B</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>SELECT STATEMENT<BR>&nbsp; SORT ORDER=20
BY<BR>&nbsp;&nbsp; TABLE ACCESS BY INDEX ROWID JAM_TRACE_SYS=20
B<BR>&nbsp;&nbsp;&nbsp;&nbsp; NESTED=20
LOOPS<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; TABLE ACCESS BY INDEX =
ROWID=20
JAM_TRACE_SYS&nbsp; =
A<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; INDEX=20
RANGE SCAN JAM_TRACE_SYS_N1&nbsp; =
A<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
INDEX RANGE SCAN JAM_TRACE_SYS_N1=20
B<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SORT=20
AGGREGATE<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 INDEX=20
RANGE SCAN JAM_TRACE_SYS_N1 C</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>In postgreSQL A and B are doing a =
cartesian=20
product<BR>then C gets executed for every row in this cartesian =
product<BR>and=20
most of the extra rows get thrown out.<BR>Is there any way to force an =
execution=20
plan like above where the correlated subquery runs before going to =
B.<BR>The=20
table is small right now, but it will grow to have millions of=20
rows<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>QUERY=20
PLAN<BR>-----------------------------------------------------------------=
------------------------------------------------------------------<BR>&nb=
sp;Sort&nbsp;=20
(cost=3D124911.81..124944.84 rows=3D13213 width=3D20) (actual=20
time=3D13096.754..13097.053 rows=3D149 loops=3D1)<BR>&nbsp;&nbsp; Sort =
Key:=20
a.seq_no<BR>&nbsp;&nbsp; -&gt;&nbsp; Nested Loop&nbsp; =
(cost=3D4.34..124007.40=20
rows=3D13213 width=3D20) (actual time=3D1948.300..13096.329 rows=3D149=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Join =
Filter:=20
(subplan)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
-&gt;&nbsp; Seq=20
Scan on jam_trace_sys b&nbsp; (cost=3D0.00..3.75 rows=3D175 width=3D16) =
(actual=20
time=3D0.005..0.534 rows=3D175=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
-&gt;&nbsp;=20
Materialize&nbsp; (cost=3D4.34..5.85 rows=3D151 width=3D16) (actual =
time=3D0.002..0.324=20
rows=3D150=20
loops=3D175)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on jam_trace_sys a&nbsp; (cost=3D0.00..4.19 =
rows=3D151=20
width=3D16) (actual time=3D0.022..0.687 rows=3D150=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Filter: (trace_id =3D =
22)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
SubPlan<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Aggregate&nbsp; (cost=3D4.67..4.67 rows=3D1 width=3D4) =
(actual=20
time=3D0.486..0.488 rows=3D1=20
loops=3D26250)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on jam_trace_sys c&nbsp; (cost=3D0.00..4.62 =
rows=3D15 width=3D4)=20
(actual time=3D0.058..0.311 rows=3D74=20
loops=3D26250)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;=20
Filter: ((trace_id =3D $0) AND (seq_no &gt; $1))<BR>&nbsp;Total runtime: =
13097.557=20
ms<BR>(13 rows)</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>pglnx01=3D&gt; \d=20
jam_trace_sys<BR>&nbsp;&nbsp;&nbsp;&nbsp; Table=20
"public.jam_trace_sys"<BR>&nbsp;&nbsp;&nbsp;&nbsp;=20
Column&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |&nbsp; Type&nbsp;&nbsp; |=20
Modifiers<BR>-----------------+---------+-----------<BR>&nbsp;trace_id&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
| integer=20
|<BR>&nbsp;seq_no&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
|=20
integer |<BR>&nbsp;cpu_utilization | integer=20
|<BR>&nbsp;gc_minor&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; | integer=20
|<BR>&nbsp;gc_major&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; | integer=20
|<BR>&nbsp;heap_used&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; | integer=20
|<BR>Indexes:<BR>&nbsp;&nbsp;&nbsp; "jam_trace_sys_n1" btree (trace_id,=20
seq_no)</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>pglnx01=3D&gt; select count(*) from =
jam_trace_Sys=20
;<BR>&nbsp;count<BR>-------<BR>&nbsp;&nbsp; 175<BR>(1 row)</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>pglnx01=3D&gt; select trace_id, =
count(*) from=20
jam_trace_sys group by trace_id ;<BR>&nbsp;trace_id |=20
count<BR>----------+-------<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 15=20
|&nbsp;&nbsp;&nbsp;&nbsp; 2<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 18=20
|&nbsp;&nbsp;&nbsp; 21<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 22 =
|&nbsp;&nbsp;=20
150<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 16 |&nbsp;&nbsp;&nbsp;&nbsp; =
2<BR>(4=20
rows)<BR></DIV></FONT></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Wed Jan  4 09:54:26 2006
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Subject: Re: improving write performance for logging application
From: Ian Westmacott <ianw@intellivid.com>
To: Steve Eckmann <eckmann@computer.org>
Cc: pgsql-performance@postgresql.org
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We have a similar application thats doing upwards of 2B inserts
per day.  We have spent a lot of time optimizing this, and found the
following to be most beneficial:

1)  use COPY (BINARY if possible)
2)  don't use triggers or foreign keys
3)  put WAL and tables on different spindles (channels if possible)
4)  put as much as you can in each COPY, and put as many COPYs as
    you can in a single transaction.
5)  watch out for XID wraparound
6)  tune checkpoint* and bgwriter* parameters for your I/O system

On Tue, 2006-01-03 at 16:44 -0700, Steve Eckmann wrote:
> I have questions about how to improve the write performance of PostgreSQL for logging data from a real-time simulation. We found that MySQL 4.1.3 could log about 1480 objects/second using MyISAM tables or about 1225 objects/second using InnoDB tables, but PostgreSQL 8.0.3 could log only about 540 objects/second. (test system: quad-Itanium2, 8GB memory, SCSI RAID, GigE connection from simulation server, nothing running except system processes and database system under test)
> 
> We also found that we could improve MySQL performance significantly using MySQL's "INSERT" command extension allowing multiple value-list tuples in a single command; the rate for MyISAM tables improved to about 2600 objects/second. PostgreSQL doesn't support that language extension. Using the COPY command instead of INSERT might help, but since rows are being generated on the fly, I don't see how to use COPY without running a separate process that reads rows from the application and uses COPY to write to the database. The application currently has two processes: the simulation and a data collector that reads events from the sim (queued in shared memory) and writes them as rows to the database, buffering as needed to avoid lost data during periods of high activity. To use COPY I think we would have to split our data collector into two processes communicating via a pipe.
> 
> Query performance is not an issue: we found that when suitable indexes are added PostgreSQL is fast enough on the kinds of queries our users make. The crux is writing rows to the database fast enough to keep up with the simulation.
> 
> Are there general guidelines for tuning the PostgreSQL server for this kind of application? The suggestions I've found include disabling fsync (done), increasing the value of wal_buffers, and moving the WAL to a different disk, but these aren't likely to produce the 3x improvement that we need. On the client side I've found only two suggestions: disable autocommit and use COPY instead of INSERT. I think I've effectively disabled autocommit by batching up to several hundred INSERT commands in each PQexec() call, and it isn’t clear that COPY is worth the effort in our application.
> 
> Thanks.
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
-- 
Ian Westmacott <ianw@intellivid.com>
Intellivid Corp.


From pgsql-performance-owner@postgresql.org  Wed Jan  4 10:00:21 2006
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From: Steve Eckmann <eckmann@computer.org>
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Tom Lane wrote:

>Steve Eckmann <eckmann@computer.org> writes:
>  
>
>>We also found that we could improve MySQL performance significantly
>>using MySQL's "INSERT" command extension allowing multiple value-list
>>tuples in a single command; the rate for MyISAM tables improved to
>>about 2600 objects/second. PostgreSQL doesn't support that language
>>extension. Using the COPY command instead of INSERT might help, but
>>since rows are being generated on the fly, I don't see how to use COPY
>>without running a separate process that reads rows from the
>>application and uses COPY to write to the database.
>>    
>>
>
>Can you conveniently alter your application to batch INSERT commands
>into transactions?  Ie
>
>	BEGIN;
>	INSERT ...;
>	... maybe 100 or so inserts ...
>	COMMIT;
>	BEGIN;
>	... lather, rinse, repeat ...
>
>This cuts down the transactional overhead quite a bit.  A downside is
>that you lose multiple rows if any INSERT fails, but then the same would
>be true of multiple VALUES lists per INSERT.
>
>			regards, tom lane
>  
>
Thanks for the suggestion, Tom. Yes, I think I could do that. But I 
thought what I was doing now was effectively the same, because the 
PostgreSQL 8.0.0 Documentation says (section 27.3.1): "It is allowed to 
include multiple SQL commands (separated by semicolons) in the command 
string. Multiple queries sent in a single PQexec call are processed in a 
single transaction...." Our simulation application has nearly 400 event 
types, each of which is a C++ class for which we have a corresponding 
database table. So every thousand events or so I issue one PQexec() call 
for each event type that has unlogged instances, sending INSERT commands 
for all instances. For example,

    PQexec(dbConn, "INSERT INTO FlyingObjectState VALUES (...); INSERT 
INTO FlyingObjectState VALUES (...); ...");

My thought was that this would be a good compromise between minimizing 
transactions (one per event class per buffering interval instead of one 
per event) and minimizing disk seeking (since all queries in a single 
transaction insert rows into the same table). Am I overlooking something 
here? One thing I haven't tried is increasing the buffering interval 
from 1000 events to, say, 10,000. It turns out that 1000 is a good 
number for Versant, the object database system we're replacing, and for 
MySQL, so I assumed it would be a good number for PostgreSQL, too.

Regards,  Steve


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Tom Lane wrote:
<blockquote cite="mid27720.1136332812@sss.pgh.pa.us" type="cite">
  <pre wrap="">Steve Eckmann <a class="moz-txt-link-rfc2396E" href="mailto:eckmann@computer.org">&lt;eckmann@computer.org&gt;</a> writes:
  </pre>
  <blockquote type="cite">
    <pre wrap="">We also found that we could improve MySQL performance significantly
using MySQL's "INSERT" command extension allowing multiple value-list
tuples in a single command; the rate for MyISAM tables improved to
about 2600 objects/second. PostgreSQL doesn't support that language
extension. Using the COPY command instead of INSERT might help, but
since rows are being generated on the fly, I don't see how to use COPY
without running a separate process that reads rows from the
application and uses COPY to write to the database.
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Can you conveniently alter your application to batch INSERT commands
into transactions?  Ie

	BEGIN;
	INSERT ...;
	... maybe 100 or so inserts ...
	COMMIT;
	BEGIN;
	... lather, rinse, repeat ...

This cuts down the transactional overhead quite a bit.  A downside is
that you lose multiple rows if any INSERT fails, but then the same would
be true of multiple VALUES lists per INSERT.

			regards, tom lane
  </pre>
</blockquote>
Thanks for the suggestion, Tom. Yes, I think I could do that. But I
thought what I was doing now was effectively the same, because the
PostgreSQL 8.0.0 Documentation says (section 27.3.1): "It is allowed to
include multiple SQL commands (separated by semicolons) in the command
string. Multiple queries sent in a single PQexec call are processed in
a single transaction...." Our simulation application has nearly 400
event types, each of which is a C++ class for which we have a
corresponding database table. So every thousand events or so I issue
one PQexec() call for each event type that has unlogged instances,
sending INSERT commands for all instances. For example,<br>
<br>
&nbsp;&nbsp;&nbsp; PQexec(dbConn, "INSERT INTO FlyingObjectState VALUES (...); INSERT
INTO FlyingObjectState VALUES (...); ...");<br>
<br>
My thought was that this would be a good compromise between minimizing
transactions (one per event class per buffering interval instead of one
per event) and minimizing disk seeking (since all queries in a single
transaction insert rows into the same table). Am I overlooking
something here? One thing I haven't tried is increasing the buffering
interval from 1000 events to, say, 10,000. It turns out that 1000 is a
good number for Versant, the object database system we're replacing,
and for MySQL, so I assumed it would be a good number for PostgreSQL,
too.<br>
<br>
Regards,&nbsp; Steve<br>
<br>
</body>
</html>

--------------060004050500060909060100--

From pgsql-performance-owner@postgresql.org  Wed Jan  4 10:08:39 2006
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From: Steve Eckmann <eckmann@computer.org>
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Steinar H. Gunderson wrote:

>On Tue, Jan 03, 2006 at 04:44:28PM -0700, Steve Eckmann wrote:
>  
>
>>Are there general guidelines for tuning the PostgreSQL server for this kind 
>>of application? The suggestions I've found include disabling fsync (done),
>>    
>>
>
>Are you sure you really want this? The results could be catastrophic in case
>of a crash.
>
>  
>
>>On the client side I've found only two suggestions: disable autocommit and 
>>use COPY instead of INSERT. I think I've effectively disabled autocommit by 
>>batching up to several hundred INSERT commands in each PQexec() call, and 
>>it isn’t clear that COPY is worth the effort in our application.
>>    
>>
>
>I'm a bit confused here: How can you batch multiple INSERTs into large
>statements for MySQL, but not batch multiple INSERTs into COPY statements for
>PostgreSQL?
>
>Anyhow, putting it all inside one transaction (or a few) is likely to help
>quite a lot, but of course less when you have fsync=false. Bunding multiple
>statements in each PQexec() call won't really give you that; you'll have to
>tell the database so explicitly.
>
>/* Steinar */
>  
>
Thanks, Steinar. I don't think we would really run with fsync off, but I 
need to document the performance tradeoffs. You're right that my 
explanation was confusing; probably because I'm confused about how to 
use COPY! I could batch multiple INSERTS using COPY statements, I just 
don't see how to do it without adding another process to read from 
STDIN, since the application that is currently the database client is 
constructing rows on the fly. I would need to get those rows into some 
process's STDIN stream or into a server-side file before COPY could be 
used, right?

You're comment about bundling multiple statements in each PQexec() call 
seems to disagree with a statement in 27.3.1 that I interpret as saying 
each PQexec() call corresponds to a single transaction. Are you sure my 
interpretation is wrong?

Regards, Steve

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Steinar H. Gunderson wrote:<br>
<blockquote cite="mid20060104000603.GA29469@uio.no" type="cite">
  <pre wrap="">On Tue, Jan 03, 2006 at 04:44:28PM -0700, Steve Eckmann wrote:
  </pre>
  <blockquote type="cite">
    <pre wrap="">Are there general guidelines for tuning the PostgreSQL server for this kind 
of application? The suggestions I've found include disabling fsync (done),
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Are you sure you really want this? The results could be catastrophic in case
of a crash.

  </pre>
  <blockquote type="cite">
    <pre wrap="">On the client side I've found only two suggestions: disable autocommit and 
use COPY instead of INSERT. I think I've effectively disabled autocommit by 
batching up to several hundred INSERT commands in each PQexec() call, and 
it isn’t clear that COPY is worth the effort in our application.
    </pre>
  </blockquote>
  <pre wrap=""><!---->
I'm a bit confused here: How can you batch multiple INSERTs into large
statements for MySQL, but not batch multiple INSERTs into COPY statements for
PostgreSQL?

Anyhow, putting it all inside one transaction (or a few) is likely to help
quite a lot, but of course less when you have fsync=false. Bunding multiple
statements in each PQexec() call won't really give you that; you'll have to
tell the database so explicitly.

/* Steinar */
  </pre>
</blockquote>
Thanks, Steinar. I don't think we would really run with fsync off, but
I need to document the performance tradeoffs. You're right that my
explanation was confusing; probably because I'm confused about how to
use COPY! I could batch multiple INSERTS using COPY statements, I just
don't see how to do it without adding another process to read from
STDIN, since the application that is currently the database client is
constructing rows on the fly. I would need to get those rows into some
process's STDIN stream or into a server-side file before COPY could be
used, right?<br>
<br>
You're comment about bundling multiple statements in each PQexec() call
seems to disagree with a statement in 27.3.1 that I interpret as saying
each PQexec() call corresponds to a single transaction. Are you sure my
interpretation is wrong?<br>
<br>
Regards, Steve
</body>
</html>

--------------070306010906040306040009--

From pgsql-performance-owner@postgresql.org  Wed Jan  4 10:13:21 2006
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dlang wrote:

>On Tue, 3 Jan 2006, Tom Lane wrote:
>
>  
>
>>Steve Eckmann <eckmann@computer.org> writes:
>>    
>>
>>>We also found that we could improve MySQL performance significantly
>>>using MySQL's "INSERT" command extension allowing multiple value-list
>>>tuples in a single command; the rate for MyISAM tables improved to
>>>about 2600 objects/second. PostgreSQL doesn't support that language
>>>extension. Using the COPY command instead of INSERT might help, but
>>>since rows are being generated on the fly, I don't see how to use COPY
>>>without running a separate process that reads rows from the
>>>application and uses COPY to write to the database.
>>>      
>>>
>>Can you conveniently alter your application to batch INSERT commands
>>into transactions?  Ie
>>
>>	BEGIN;
>>	INSERT ...;
>>	... maybe 100 or so inserts ...
>>	COMMIT;
>>	BEGIN;
>>	... lather, rinse, repeat ...
>>
>>This cuts down the transactional overhead quite a bit.  A downside is
>>that you lose multiple rows if any INSERT fails, but then the same would
>>be true of multiple VALUES lists per INSERT.
>>    
>>
>
>Steve, you mentioned that you data collector buffers the data before
>sending it to the database, modify it so that each time it goes to send
>things to the database you send all the data that's in the buffer as a
>single transaction.
>
>I am working on useing postgres to deal with log data and wrote a simple
>perl script that read in the log files a line at a time, and then wrote
>them 1000 at a time to the database. On a dual Opteron 240 box with 2G of
>ram 1x 15krpm SCSI drive (and a untuned postgress install with the compile
>time defaults) I was getting 5000-8000 lines/sec (I think this was with
>fsync disabled, but I don't remember for sure). and postgres was
>complaining that it was overrunning it's log sizes (which limits the speed
>as it then has to pause to flush the logs)
>
>the key thing is to send multiple lines with one transaction as tom shows
>above.
>
>David Lang
>
Thanks, David. I will look more carefully at how to batch multiple rows 
per PQexec() call.  Regards, Steve.

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dlang wrote:<br>
<blockquote
 cite="midPine.LNX.4.44.0601031916340.29612-100000@web.lang.hm"
 type="cite">
  <pre wrap="">
On Tue, 3 Jan 2006, Tom Lane wrote:

  </pre>
  <blockquote type="cite">
    <pre wrap="">Steve Eckmann <a class="moz-txt-link-rfc2396E" href="mailto:eckmann@computer.org">&lt;eckmann@computer.org&gt;</a> writes:
    </pre>
    <blockquote type="cite">
      <pre wrap="">We also found that we could improve MySQL performance significantly
using MySQL's "INSERT" command extension allowing multiple value-list
tuples in a single command; the rate for MyISAM tables improved to
about 2600 objects/second. PostgreSQL doesn't support that language
extension. Using the COPY command instead of INSERT might help, but
since rows are being generated on the fly, I don't see how to use COPY
without running a separate process that reads rows from the
application and uses COPY to write to the database.
      </pre>
    </blockquote>
    <pre wrap="">Can you conveniently alter your application to batch INSERT commands
into transactions?  Ie

	BEGIN;
	INSERT ...;
	... maybe 100 or so inserts ...
	COMMIT;
	BEGIN;
	... lather, rinse, repeat ...

This cuts down the transactional overhead quite a bit.  A downside is
that you lose multiple rows if any INSERT fails, but then the same would
be true of multiple VALUES lists per INSERT.
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Steve, you mentioned that you data collector buffers the data before
sending it to the database, modify it so that each time it goes to send
things to the database you send all the data that's in the buffer as a
single transaction.

I am working on useing postgres to deal with log data and wrote a simple
perl script that read in the log files a line at a time, and then wrote
them 1000 at a time to the database. On a dual Opteron 240 box with 2G of
ram 1x 15krpm SCSI drive (and a untuned postgress install with the compile
time defaults) I was getting 5000-8000 lines/sec (I think this was with
fsync disabled, but I don't remember for sure). and postgres was
complaining that it was overrunning it's log sizes (which limits the speed
as it then has to pause to flush the logs)

the key thing is to send multiple lines with one transaction as tom shows
above.

David Lang</pre>
</blockquote>
Thanks, David. I will look more carefully at how to batch multiple rows
per PQexec() call.&nbsp; Regards, Steve.<br>
</body>
</html>

--------------050703080005020101070803--

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From: Steve Eckmann <eckmann@computer.org>
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To: Ian Westmacott <ianw@intellivid.com>
CC: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application
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Ian Westmacott wrote:

>We have a similar application thats doing upwards of 2B inserts
>per day.  We have spent a lot of time optimizing this, and found the
>following to be most beneficial:
>
>1)  use COPY (BINARY if possible)
>2)  don't use triggers or foreign keys
>3)  put WAL and tables on different spindles (channels if possible)
>4)  put as much as you can in each COPY, and put as many COPYs as
>    you can in a single transaction.
>5)  watch out for XID wraparound
>6)  tune checkpoint* and bgwriter* parameters for your I/O system
>
Thanks, Ian. I will look at how to implement your suggestions.

Regards, Steve

From pgsql-performance-owner@postgresql.org  Wed Jan  4 10:29:04 2006
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Date: Wed, 04 Jan 2006 09:29:00 -0500
To: Ian Westmacott <ianw@intellivid.com>,pgsql-performance@postgresql.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: improving write performance for logging
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2B is a lot of inserts.  If you had to guess,=20
what do you think is the maximum number of inserts you could do in a day?

How large is each record being inserted?

How much can you put in a COPY and how many COPYs=20
can you put into a transactions?

What values are you using for bgwriter* and checkpoint*?

What HW on you running on and what kind of performance do you typically get?

Inquiring minds definitely want to know ;-)
Ron


At 08:54 AM 1/4/2006, Ian Westmacott wrote:
>We have a similar application thats doing upwards of 2B inserts
>per day.  We have spent a lot of time optimizing this, and found the
>following to be most beneficial:
>
>1)  use COPY (BINARY if possible)
>2)  don't use triggers or foreign keys
>3)  put WAL and tables on different spindles (channels if possible)
>4)  put as much as you can in each COPY, and put as many COPYs as
>     you can in a single transaction.
>5)  watch out for XID wraparound
>6)  tune checkpoint* and bgwriter* parameters for your I/O system
>
>On Tue, 2006-01-03 at 16:44 -0700, Steve Eckmann wrote:
> > I have questions about how to improve the=20
> write performance of PostgreSQL for logging=20
> data from a real-time simulation. We found that=20
> MySQL 4.1.3 could log about 1480 objects/second=20
> using MyISAM tables or about 1225=20
> objects/second using InnoDB tables, but=20
> PostgreSQL 8.0.3 could log only about 540=20
> objects/second. (test system: quad-Itanium2,=20
> 8GB memory, SCSI RAID, GigE connection from=20
> simulation server, nothing running except=20
> system processes and database system under test)
> >
> > We also found that we could improve MySQL=20
> performance significantly using MySQL's=20
> "INSERT" command extension allowing multiple=20
> value-list tuples in a single command; the rate=20
> for MyISAM tables improved to about 2600=20
> objects/second. PostgreSQL doesn't support that=20
> language extension. Using the COPY command=20
> instead of INSERT might help, but since rows=20
> are being generated on the fly, I don't see how=20
> to use COPY without running a separate process=20
> that reads rows from the application and uses=20
> COPY to write to the database. The application=20
> currently has two processes: the simulation and=20
> a data collector that reads events from the sim=20
> (queued in shared memory) and writes them as=20
> rows to the database, buffering as needed to=20
> avoid lost data during periods of high=20
> activity. To use COPY I think we would have to=20
> split our data collector into two processes communicating via a pipe.
> >
> > Query performance is not an issue: we found=20
> that when suitable indexes are added PostgreSQL=20
> is fast enough on the kinds of queries our=20
> users make. The crux is writing rows to the=20
> database fast enough to keep up with the simulation.
> >
> > Are there general guidelines for tuning the=20
> PostgreSQL server for this kind of application?=20
> The suggestions I've found include disabling=20
> fsync (done), increasing the value of=20
> wal_buffers, and moving the WAL to a different=20
> disk, but these aren't likely to produce the 3x=20
> improvement that we need. On the client side=20
> I've found only two suggestions: disable=20
> autocommit and use COPY instead of INSERT. I=20
> think I've effectively disabled autocommit by=20
> batching up to several hundred INSERT commands=20
> in each PQexec() call, and it isn=E2=80=99t clear=20
> that COPY is worth the effort in our application.
> >
> > Thanks.
> >
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 2: Don't 'kill -9' the postmaster
>--
>Ian Westmacott <ianw@intellivid.com>
>Intellivid Corp.
>
>
>---------------------------(end of broadcast)---------------------------
>TIP 4: Have you searched our list archives?
>
>                http://archives.postgresql.org




From pgsql-performance-owner@postgresql.org  Wed Jan  4 11:39:28 2006
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To: Steve Eckmann <eckmann@computer.org>
cc: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application 
In-reply-to: <43BBD4EC.5020207@computer.org> 
References: <43BB0C5C.8020207@computer.org> <27720.1136332812@sss.pgh.pa.us>
	<43BBD4EC.5020207@computer.org>
Comments: In-reply-to Steve Eckmann <eckmann@computer.org>
	message dated "Wed, 04 Jan 2006 07:00:12 -0700"
Date: Wed, 04 Jan 2006 10:39:25 -0500
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Steve Eckmann <eckmann@computer.org> writes:
> Thanks for the suggestion, Tom. Yes, I think I could do that. But I 
> thought what I was doing now was effectively the same, because the 
> PostgreSQL 8.0.0 Documentation says (section 27.3.1): "It is allowed to 
> include multiple SQL commands (separated by semicolons) in the command 
> string. Multiple queries sent in a single PQexec call are processed in a 
> single transaction...." Our simulation application has nearly 400 event 
> types, each of which is a C++ class for which we have a corresponding 
> database table. So every thousand events or so I issue one PQexec() call 
> for each event type that has unlogged instances, sending INSERT commands 
> for all instances. For example,

>     PQexec(dbConn, "INSERT INTO FlyingObjectState VALUES (...); INSERT 
> INTO FlyingObjectState VALUES (...); ...");

Hmm.  I'm not sure if that's a good idea or not.  You're causing the
server to take 1000 times the normal amount of memory to hold the
command parsetrees, and if there are any O(N^2) behaviors in parsing
you could be getting hurt badly by that.  (I'd like to think there are
not, but would definitely not swear to it.)  OTOH you're reducing the
number of network round trips which is a good thing.  Have you actually
measured to see what effect this approach has?  It might be worth
building a test server with profiling enabled to see if the use of such
long command strings creates any hot spots in the profile.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan  4 11:40:29 2006
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Date: Wed, 4 Jan 2006 09:40:31 -0600
From: Kelly Burkhart <kelly@kkcsm.net>
To: Steve Eckmann <eckmann@computer.org>
Subject: Re: improving write performance for logging application
Cc: pgsql-performance@postgresql.org
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On 1/4/06, Steve Eckmann <eckmann@computer.org> wrote:
>
> Thanks, Steinar. I don't think we would really run with fsync off, but I
> need to document the performance tradeoffs. You're right that my explanat=
ion
> was confusing; probably because I'm confused about how to use COPY! I cou=
ld
> batch multiple INSERTS using COPY statements, I just don't see how to do =
it
> without adding another process to read from STDIN, since the application
> that is currently the database client is constructing rows on the fly. I
> would need to get those rows into some process's STDIN stream or into a
> server-side file before COPY could be used, right?


Steve,

You can use copy without resorting to another process.  See the libpq
documentation for 'Functions Associated with the copy Command".  We do
something like this:

char *mbuf;

// allocate space and fill mbuf with appropriately formatted data somehow

PQexec( conn, "begin" );
PQexec( conn, "copy mytable from stdin" );
PQputCopyData( conn, mbuf, strlen(mbuf) );
PQputCopyEnd( conn, NULL );
PQexec( conn, "commit" );

-K

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On 1/4/06, <b class=3D"gmail_sendername">Steve Eckmann</b> &lt;<a href=3D"m=
ailto:eckmann@computer.org">eckmann@computer.org</a>&gt; wrote:<div><span c=
lass=3D"gmail_quote"></span><blockquote class=3D"gmail_quote" style=3D"bord=
er-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-l=
eft: 1ex;">
Thanks, Steinar. I don't think we would really run with fsync off, but
I need to document the performance tradeoffs. You're right that my
explanation was confusing; probably because I'm confused about how to
use COPY! I could batch multiple INSERTS using COPY statements, I just
don't see how to do it without adding another process to read from
STDIN, since the application that is currently the database client is
constructing rows on the fly. I would need to get those rows into some
process's STDIN stream or into a server-side file before COPY could be
used, right?</blockquote><div><br>
Steve,<br>
<br>
You can use copy without resorting to another process.&nbsp; See the
libpq documentation for 'Functions Associated with the copy
Command&quot;.&nbsp; We do something like this:<br>
<br>
</div></div>char *mbuf;<br>
<br>
// allocate space and fill mbuf with appropriately formatted data somehow<b=
r>
<br>
PQexec( conn, &quot;begin&quot; );<br>
PQexec( conn, &quot;copy mytable from stdin&quot; );<br>
PQputCopyData( conn, mbuf, strlen(mbuf) );<br>
PQputCopyEnd( conn, NULL );<br>
PQexec( conn, &quot;commit&quot; );<br>
<br>
-K<br>

------=_Part_2696_747897.1136389231093--

From pgsql-performance-owner@postgresql.org  Wed Jan  4 12:00:42 2006
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Subject: Re: improving write performance for logging
From: Ian Westmacott <ianw@intellivid.com>
To: Ron <rjpeace@earthlink.net>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <7.0.1.0.2.20060104092139.01c37da0@earthlink.net>
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	<7.0.1.0.2.20060104092139.01c37da0@earthlink.net>
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Organization: Intellivid Corp.
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On Wed, 2006-01-04 at 09:29 -0500, Ron wrote:
> 2B is a lot of inserts.  If you had to guess, 
> what do you think is the maximum number of inserts you could do in a day?

It seems we are pushing it there.  Our intentions are to scale much
further, but our plans are to distribute at this point.

> How large is each record being inserted?

They are small: 32 (data) bytes.

> How much can you put in a COPY and how many COPYs 
> can you put into a transactions?

These are driven by the application; we do about 60 COPYs and a couple
dozen INSERT/UPDATE/DELETEs in a single transaction.  Each COPY is
doing a variable number of rows, up to several hundred.  We do 15 of
these transactions per second.

> What values are you using for bgwriter* and checkpoint*?

bgwriter is 100%/500 pages, and checkpoint is 50 segments/300 seconds.
wal_buffers doesn't do much for us, and fsync is enabled.

> What HW on you running on and what kind of performance do you typically get?

The WAL is a 2-spindle (SATA) RAID0 with its own controller (ext3).
The tables are on a 10-spindle (SCSI) RAID50 with dual U320
controllers (XFS).  This is overkill for writing and querying the data,
but we need to constantly ANALYZE and VACUUM in the
background without interrupting the inserts (the app is 24x7).  The
databases are 4TB, so these operations can be lengthy.

-- 
Ian Westmacott <ianw@intellivid.com>
Intellivid Corp.


From pgsql-performance-owner@postgresql.org  Wed Jan  4 18:49:51 2006
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Subject: Help in avoiding a query 'Warm-Up' period/shared buffer cache
Date: Wed, 4 Jan 2006 14:49:43 -0800
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Hello,

We have a web-application running against a postgres 8.1 database, and 
basically, every time I run a report after no other reports have been run for 
several hours, the report will take significantly longer (e.g. 30 seconds), 
then if I re-run the report again, or run the report when the web-application 
has been used recently (< 1 second).

Keep in mind that our web-app might issue 30 or more individual queries to 
return a given report and that this behavior is not just isolated to a single 
report-type - it basically happens for any of the reports after the web-app 
has been inactive.  Also, I can trace it back to the timing of the underlying 
queries, which show this same behavior (e.g. it's not because of overhead in 
our web-app).

So, it appears to be some sort of caching issue.  I'm not 100% clear on how 
the shared buffer cache works, and what we might do to make sure that we 
don't have these periods where queries take a long time.  Since our users' 
typical usage scenario is to not use the web-app for a long time and then 
come back and use it, if reports which generally take a second are taking 30 
seconds, we have a real problem.

I have isolated a single example of one such query which is very slow when no 
other queries have been run, and then speeds up significantly on the second 
run.

First run, after a night of inactivity:

explain analyze SELECT average_size, end_time FROM 1min_events WHERE file_id = 
'137271' AND end_time > now() - interval '2 minutes' ORDER BY end_time DESC 
LIMIT 1;

 Limit  (cost=47.06..47.06 rows=1 width=24) (actual time=313.585..313.585 
rows=1 loops=1)
   ->  Sort  (cost=47.06..47.06 rows=1 width=24) (actual time=313.584..313.584 
rows=1 loops=1)
         Sort Key: end_time
         ->  Bitmap Heap Scan on 1min_events  (cost=44.03..47.05 rows=1 
width=24) (actual time=313.562..313.568 rows=2 loops=1)
               Recheck Cond: ((end_time > (now() - '00:02:00'::interval)) AND 
(file_id = 137271))
               ->  BitmapAnd  (cost=44.03..44.03 rows=1 width=0) (actual 
time=313.551..313.551 rows=0 loops=1)
                     ->  Bitmap Index Scan on 1min_events_end_idx  
(cost=0.00..5.93 rows=551 width=0) (actual time=0.076..0.076 rows=46 loops=1)
                           Index Cond: (end_time > (now() - 
'00:02:00'::interval))
                     ->  Bitmap Index Scan on 1min_events_file_id_begin_idx  
(cost=0.00..37.85 rows=3670 width=0) (actual time=313.468..313.468 rows=11082 
loops=1)
                           Index Cond: (file_id = 137271)
 Total runtime: 313.643 ms
(11 rows)

Second run, after that:

 explain analyze SELECT average_size, end_time FROM 1min_events WHERE file_id 
= '137271' AND end_time > now() - interval '2 minutes' ORDER BY end_time DESC 
LIMIT 1;

 Limit  (cost=47.06..47.06 rows=1 width=24) (actual time=2.209..2.209 rows=1 
loops=1)
   ->  Sort  (cost=47.06..47.06 rows=1 width=24) (actual time=2.208..2.208 
rows=1 loops=1)
         Sort Key: end_time
         ->  Bitmap Heap Scan on 1min_events  (cost=44.03..47.05 rows=1 
width=24) (actual time=2.192..2.194 rows=2 loops=1)
               Recheck Cond: ((end_time > (now() - '00:02:00'::interval)) AND 
(file_id = 137271))
               ->  BitmapAnd  (cost=44.03..44.03 rows=1 width=0) (actual 
time=2.186..2.186 rows=0 loops=1)
                     ->  Bitmap Index Scan on 1min_events_end_idx  
(cost=0.00..5.93 rows=551 width=0) (actual time=0.076..0.076 rows=46 loops=1)
                           Index Cond: (end_time > (now() - 
'00:02:00'::interval))
                     ->  Bitmap Index Scan on 1min_events_file_id_begin_idx  
(cost=0.00..37.85 rows=3670 width=0) (actual time=2.106..2.106 rows=11082 
loops=1)
                           Index Cond: (file_id = 137271)
 Total runtime: 2.276 ms
(11 rows)

One of the things that is perplexing about the initial slowness of this query 
is that it's accessing the most recent rows in a given table (e.g. those in 
the last 2 minutes).  So, I would expect the OS cache to be updated with 
these new rows.

Some general information about the server / db:

1) The database is 25G, and has about 60 tables - some very small, but several 
> 5 MM rows.

2) The table I am querying against above (1min_events) has 5.5 MM rows, but is 
indexed on end_time, as well as a compound index on file_id, begin_time

3) The following are running on the server that holds the db:

a) A program which is reading files and making several (5-10) database calls 
per minute (these calls tend to take < 100 ms each).  These calls are 
inserting 10's of rows into several of the tables.

b) An apache web-server

c) The 8.1 postgres DB

d) we are running periodic CRON jobs (generally at 11pm, 1 am and 3am) that 
truncate some of the older data

e) we have autovacuum on with a 60 second naptime and and low scale factors 
0.2, so analyzes and vacuums happen throughout the day - vacuums are 
generally triggered by the truncate CRON jobs too.

4) Some of our config settings:

shared_buffers = 8192
work_mem = 8192 

Total RAM on server is 1 Gig


Basically any advice as to what to look at to avoid this situation would be 
greatly appreciated.  Is this simply a matter of tuning the shared_buffers 
parameter?  If not, is scheduling a set of queries to force the proper 
loading of the cache a logical solution?

Thanks in advance,


Mark


From pgsql-performance-owner@postgresql.org  Wed Jan  4 20:16:53 2006
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Date: Wed, 04 Jan 2006 17:16:45 -0700
From: Steve Eckmann <eckmann@computer.org>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application
References: <43BB0C5C.8020207@computer.org> <27720.1136332812@sss.pgh.pa.us>
	<43BBD4EC.5020207@computer.org> <2898.1136389165@sss.pgh.pa.us>
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Tom Lane wrote:

>Steve Eckmann <eckmann@computer.org> writes:
>  
>
>> <>Thanks for the suggestion, Tom. Yes, I think I could do that. But I
>> thought what I was doing now was effectively the same, because the
>> PostgreSQL 8.0.0 Documentation says (section 27.3.1): "It is allowed to
>> include multiple SQL commands (separated by semicolons) in the command
>> string. Multiple queries sent in a single PQexec call are processed in a
>> single transaction...." Our simulation application has nearly 400 event
>> types, each of which is a C++ class for which we have a corresponding
>> database table. So every thousand events or so I issue one PQexec() call
>> for each event type that has unlogged instances, sending INSERT commands
>> for all instances. For example,
>
>>    PQexec(dbConn, "INSERT INTO FlyingObjectState VALUES (...); INSERT 
>>INTO FlyingObjectState VALUES (...); ...");
>>    
>>
>
>Hmm.  I'm not sure if that's a good idea or not.  You're causing the
>server to take 1000 times the normal amount of memory to hold the
>command parsetrees, and if there are any O(N^2) behaviors in parsing
>you could be getting hurt badly by that.  (I'd like to think there are
>not, but would definitely not swear to it.)  OTOH you're reducing the
>number of network round trips which is a good thing.  Have you actually
>measured to see what effect this approach has?  It might be worth
>building a test server with profiling enabled to see if the use of such
>long command strings creates any hot spots in the profile.
>
>			regards, tom lane
>  
>
No, I haven't measured it. I will compare this approach with others that 
have been suggested. Thanks.  -steve

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Tom Lane wrote:
<blockquote cite="mid2898.1136389165@sss.pgh.pa.us" type="cite">
  <pre wrap="">Steve Eckmann <a class="moz-txt-link-rfc2396E" href="mailto:eckmann@computer.org">&lt;eckmann@computer.org&gt;</a> writes:
  </pre>
  <blockquote type="cite"><>Thanks for the suggestion, Tom. Yes, I
think I could do that. But I <br>
thought what I was doing now was effectively the same, because the <br>
PostgreSQL 8.0.0 Documentation says (section 27.3.1): "It is allowed to
    <br>
include multiple SQL commands (separated by semicolons) in the command <br>
string. Multiple queries sent in a single PQexec call are processed in
a <br>
single transaction...." Our simulation application has nearly 400 event
    <br>
types, each of which is a C++ class for which we have a corresponding <br>
database table. So every thousand events or so I issue one PQexec()
call <br>
for each event type that has unlogged instances, sending INSERT
commands <br>
for all instances. For example,<!----><br>
    </></blockquote>
  <blockquote type="cite">
    <pre wrap="">    PQexec(dbConn, "INSERT INTO FlyingObjectState VALUES (...); INSERT 
INTO FlyingObjectState VALUES (...); ...");
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Hmm.  I'm not sure if that's a good idea or not.  You're causing the
server to take 1000 times the normal amount of memory to hold the
command parsetrees, and if there are any O(N^2) behaviors in parsing
you could be getting hurt badly by that.  (I'd like to think there are
not, but would definitely not swear to it.)  OTOH you're reducing the
number of network round trips which is a good thing.  Have you actually
measured to see what effect this approach has?  It might be worth
building a test server with profiling enabled to see if the use of such
long command strings creates any hot spots in the profile.

			regards, tom lane
  </pre>
</blockquote>
No, I haven't measured it. I will compare this approach with others
that have been suggested. Thanks.&nbsp; -steve<br>
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From pgsql-performance-owner@postgresql.org  Wed Jan  4 20:19:15 2006
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CC: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging application
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Kelly Burkhart wrote:

> On 1/4/06, Steve Eckmann <eckmann@computer.org 
> <mailto:eckmann@computer.org>> wrote:
>
>     Thanks, Steinar. I don't think we would really run with fsync off,
>     but I need to document the performance tradeoffs. You're right
>     that my explanation was confusing; probably because I'm confused
>     about how to use COPY! I could batch multiple INSERTS using COPY
>     statements, I just don't see how to do it without adding another
>     process to read from STDIN, since the application that is
>     currently the database client is constructing rows on the fly. I
>     would need to get those rows into some process's STDIN stream or
>     into a server-side file before COPY could be used, right?
>
>
> Steve,
>
> You can use copy without resorting to another process.  See the libpq 
> documentation for 'Functions Associated with the copy Command".  We do 
> something like this:
>
> char *mbuf;
>
> // allocate space and fill mbuf with appropriately formatted data somehow
>
> PQexec( conn, "begin" );
> PQexec( conn, "copy mytable from stdin" );
> PQputCopyData( conn, mbuf, strlen(mbuf) );
> PQputCopyEnd( conn, NULL );
> PQexec( conn, "commit" );
>
> -K

Thanks for the concrete example, Kelly. I had read the relevant libpq 
doc but didn't put the pieces together.

Regards,  Steve

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Kelly Burkhart wrote:<br>
<blockquote
 cite="midfa1e4ce70601040740t7f20ac13w9fddc80c10921c6@mail.gmail.com"
 type="cite">On 1/4/06, <b class="gmail_sendername">Steve Eckmann</b>
&lt;<a href="mailto:eckmann@computer.org">eckmann@computer.org</a>&gt;
wrote:
  <div><span class="gmail_quote"></span>
  <blockquote class="gmail_quote"
 style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Thanks,
Steinar. I don't think we would really run with fsync off, but
I need to document the performance tradeoffs. You're right that my
explanation was confusing; probably because I'm confused about how to
use COPY! I could batch multiple INSERTS using COPY statements, I just
don't see how to do it without adding another process to read from
STDIN, since the application that is currently the database client is
constructing rows on the fly. I would need to get those rows into some
process's STDIN stream or into a server-side file before COPY could be
used, right?</blockquote>
  <div><br>
Steve,<br>
  <br>
You can use copy without resorting to another process.&nbsp; See the
libpq documentation for 'Functions Associated with the copy
Command".&nbsp; We do something like this:<br>
  <br>
  </div>
  </div>
char *mbuf;<br>
  <br>
// allocate space and fill mbuf with appropriately formatted data
somehow<br>
  <br>
PQexec( conn, "begin" );<br>
PQexec( conn, "copy mytable from stdin" );<br>
PQputCopyData( conn, mbuf, strlen(mbuf) );<br>
PQputCopyEnd( conn, NULL );<br>
PQexec( conn, "commit" );<br>
  <br>
-K<br>
</blockquote>
Thanks for the concrete example, Kelly. I had read the relevant libpq
doc but didn't put the pieces together.<br>
<br>
Regards,&nbsp; Steve<br>
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From pgsql-patches-owner@postgresql.org  Wed Jan  4 20:40:18 2006
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From: Bruce Momjian <pgman@candle.pha.pa.us>
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Subject: Re: Stats collector performance improvement
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To: Bruce Momjian <pgman@candle.pha.pa.us>
Date: Wed, 4 Jan 2006 19:39:42 -0500 (EST)
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Bruce Momjian wrote:
> I did some research on this because the numbers Tom quotes indicate there
> is something wrong in the way we process stats_command_string
> statistics.
> 
...
> This sends 10,000 "SELECT 1" queries to the backend, and reports the
> execution time.  I found that without stats_command_string defined, it
> ran in 3.5 seconds.  With stats_command_string defined, it took 5.5
> seconds, meaning the command string is causing a 57% slowdown.  That is
> way too much considering that the SELECT 1 has to be send from psql to
> the backend, parsed, optimized, and executed, and the result returned to
> the psql, while stats_command_string only has to send a string to a
> backend collector.  There is _no_ way that collector should take 57% of
> the time it takes to run the actual query.

I have updated information on this performance issue.  It seems it is
the blocking activity of recv() that is slowing down the buffer process
and hence the backends.  Basically, I found if I use select() or recv()
to block until data arrives, I see the huge performance loss reported
above.  If I loop over the recv() call in non-blocking mode, I see
almost no performance hit from stats_command_string (no backend
slowdown), but of course that consumes all the CPU (bad).  What I found
worked perfectly was to do a non-blocking recv(), and if no data was
returned, change the socket to blocking mode and loop back over the
recv().  This allowed for no performance loss, and prevented infinite
looping over the recv() call.

My theory is that the kernel blocking logic of select() or recv() is
somehow locking up the socket for a small amount of time, therefore
slowing down the backend.  With the on/off blocking, the packets arrive
in groups, we get a few packets then block when nothing is available. 

The test program:

	TMPFILE=/tmp/pgstat.sql
	export TMPFILE
	
	if [ ! -f $TMPFILE ]
	then	i=0
		while [ $i -lt 10000 ]
		do
			i=`expr $i + 1`
			echo "SELECT 1;"
		done > $TMPFILE
	fi
	
	time psql test < $TMPFILE >/dev/null

is basically sending 30k packets of roughly 26 bytes each, or roughly
800k in 3.5 seconds, meaning there is a packet every 0.0001 seconds.  I
wouldn't have thought that was too much volume for a dual Xeon BSD
machine, but it seems it might be.  Tom seeing 44% slowdown from pgbench
means Linux might have an issue too.

Two patches are attached.  The first patch shows the use of the on/off
blocking method to have almost zero overhead for reading from the
socket.  (The packets are discarded.)  The second patch removes the
buffer process entirely and uses the on/off buffering to process the
incoming packets.  I tried running two test scripts simultaneously and
saw almost no packet loss.  Also keep in mind we are writing the stat
file twice a second, which might need to be pushed into a separate
process.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.118
diff -c -c -r1.118 pgstat.c
*** src/backend/postmaster/pgstat.c	3 Jan 2006 19:54:08 -0000	1.118
--- src/backend/postmaster/pgstat.c	4 Jan 2006 23:22:44 -0000
***************
*** 1839,1845 ****
  	int			msg_recv = 0;	/* next receive index */
  	int			msg_have = 0;	/* number of bytes stored */
  	bool		overflow = false;
! 
  	/*
  	 * Identify myself via ps
  	 */
--- 1839,1847 ----
  	int			msg_recv = 0;	/* next receive index */
  	int			msg_have = 0;	/* number of bytes stored */
  	bool		overflow = false;
! 	bool		is_block_mode = false;
! 	int			cnt = 0, bloops = 0, nbloops = 0;
! 	
  	/*
  	 * Identify myself via ps
  	 */
***************
*** 1870,1875 ****
--- 1872,1921 ----
  	 */
  	msgbuffer = (char *) palloc(PGSTAT_RECVBUFFERSZ);
  
+ 
+ 	while (1)
+ 	{
+ #if 0
+ 		  FD_ZERO(&rfds);
+ 		  FD_ZERO(&wfds);
+ 		  maxfd = -1;
+ 			  FD_SET(pgStatSock, &rfds);
+ 			  maxfd = pgStatSock;
+ 	
+ 		  timeout.tv_sec = 0;
+ 		  timeout.tv_usec = 0;
+ 	
+ 		  select(maxfd + 1, &rfds, &wfds, NULL, &timeout);
+ #endif
+ 	
+ 			  if (is_block_mode)
+ 				  bloops++;
+ 			  else
+ 				  nbloops++;
+ 	
+ 			  len = recv(pgStatSock, (char *) &input_buffer,
+ 						 sizeof(PgStat_Msg), 0);
+ 			  if (len > 0)
+ 				  cnt += len;
+ 	
+ //fprintf(stderr, "len = %d, errno = %d\n", len, errno);
+ 	
+ 			  if (len > 0 && is_block_mode)
+ 			  {
+ 				  pg_set_noblock(pgStatSock);
+ 				  is_block_mode = false;
+ 			  }
+ 			  else if (len < 0 && errno == EAGAIN && !is_block_mode)
+ 			  {
+ 				  pg_set_block(pgStatSock);
+ 				  is_block_mode = true;
+ 			  }
+ //			  if ((bloops + nbloops)  % 1000 == 0)
+ //				  fprintf(stderr, "cnt = %d, len = %d, bloops = %d, nbloops = %d\n", cnt, len, bloops, nbloops);
+ 	}
+ 	
+ 	exit(1);
+ 
  	/*
  	 * Loop forever
  	 */

--ELM1136421582-25820-0_
Content-Transfer-Encoding: 7bit
Content-Type: text/plain
Content-Disposition: inline; filename="/pgpatches/stat.nobuffer"

Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.118
diff -c -c -r1.118 pgstat.c
*** src/backend/postmaster/pgstat.c	3 Jan 2006 19:54:08 -0000	1.118
--- src/backend/postmaster/pgstat.c	4 Jan 2006 23:06:26 -0000
***************
*** 109,117 ****
   * ----------
   */
  NON_EXEC_STATIC int pgStatSock = -1;
- NON_EXEC_STATIC int pgStatPipe[2] = {-1, -1};
  static struct sockaddr_storage pgStatAddr;
- static pid_t pgStatCollectorPid = 0;
  
  static time_t last_pgstat_start_time;
  
--- 109,115 ----
***************
*** 166,172 ****
  NON_EXEC_STATIC void PgstatBufferMain(int argc, char *argv[]);
  NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]);
  static void force_statwrite(SIGNAL_ARGS);
- static void pgstat_recvbuffer(void);
  static void pgstat_exit(SIGNAL_ARGS);
  static void pgstat_die(SIGNAL_ARGS);
  static void pgstat_beshutdown_hook(int code, Datum arg);
--- 164,169 ----
***************
*** 1491,1536 ****
  	pgstat_parseArgs(argc, argv);
  #endif
  
- 	/*
- 	 * Start a buffering process to read from the socket, so we have a little
- 	 * more time to process incoming messages.
- 	 *
- 	 * NOTE: the process structure is: postmaster is parent of buffer process
- 	 * is parent of collector process.	This way, the buffer can detect
- 	 * collector failure via SIGCHLD, whereas otherwise it wouldn't notice
- 	 * collector failure until it tried to write on the pipe.  That would mean
- 	 * that after the postmaster started a new collector, we'd have two buffer
- 	 * processes competing to read from the UDP socket --- not good.
- 	 */
- 	if (pgpipe(pgStatPipe) < 0)
- 		ereport(ERROR,
- 				(errcode_for_socket_access(),
- 				 errmsg("could not create pipe for statistics buffer: %m")));
- 
  	/* child becomes collector process */
! #ifdef EXEC_BACKEND
! 	pgStatCollectorPid = pgstat_forkexec(STAT_PROC_COLLECTOR);
! #else
! 	pgStatCollectorPid = fork();
! #endif
! 	switch (pgStatCollectorPid)
! 	{
! 		case -1:
! 			ereport(ERROR,
! 					(errmsg("could not fork statistics collector: %m")));
! 
! #ifndef EXEC_BACKEND
! 		case 0:
! 			/* child becomes collector process */
! 			PgstatCollectorMain(0, NULL);
! 			break;
! #endif
! 
! 		default:
! 			/* parent becomes buffer process */
! 			closesocket(pgStatPipe[0]);
! 			pgstat_recvbuffer();
! 	}
  	exit(0);
  }
  
--- 1488,1495 ----
  	pgstat_parseArgs(argc, argv);
  #endif
  
  	/* child becomes collector process */
! 	PgstatCollectorMain(0, NULL);
  	exit(0);
  }
  
***************
*** 1548,1559 ****
  PgstatCollectorMain(int argc, char *argv[])
  {
  	PgStat_Msg	msg;
- 	fd_set		rfds;
- 	int			readPipe;
- 	int			len = 0;
- 	struct itimerval timeval;
  	HASHCTL		hash_ctl;
  	bool		need_timer = false;
  	
  	MyProcPid = getpid();		/* reset MyProcPid */
  
--- 1507,1517 ----
  PgstatCollectorMain(int argc, char *argv[])
  {
  	PgStat_Msg	msg;
  	HASHCTL		hash_ctl;
  	bool		need_timer = false;
+ 	struct itimerval timeval;
+ 	bool		is_block_mode = false;
+ 	int			loops = 0;
  	
  	MyProcPid = getpid();		/* reset MyProcPid */
  
***************
*** 1587,1596 ****
  	pgstat_parseArgs(argc, argv);
  #endif
  
- 	/* Close unwanted files */
- 	closesocket(pgStatPipe[1]);
- 	closesocket(pgStatSock);
- 
  	/*
  	 * Identify myself via ps
  	 */
--- 1545,1550 ----
***************
*** 1626,1791 ****
  	pgStatBeTable = (PgStat_StatBeEntry *)
  		palloc0(sizeof(PgStat_StatBeEntry) * MaxBackends);
  
- 	readPipe = pgStatPipe[0];
- 
  	/*
  	 * Process incoming messages and handle all the reporting stuff until
  	 * there are no more messages.
  	 */
  	for (;;)
  	{
  		if (need_statwrite)
  		{
! 			pgstat_write_statsfile();
  			need_statwrite = false;
  			need_timer = true;
  		}
  
! 		/*
! 		 * Setup the descriptor set for select(2)
! 		 */
! 		FD_ZERO(&rfds);
! 		FD_SET(readPipe, &rfds);
! 
! 		/*
! 		 * Now wait for something to do.
! 		 */
! 		if (select(readPipe + 1, &rfds, NULL, NULL, NULL) < 0)
  		{
! 			if (errno == EINTR)
! 				continue;
! 			ereport(ERROR,
! 					(errcode_for_socket_access(),
! 					 errmsg("select() failed in statistics collector: %m")));
  		}
  
! 		/*
! 		 * Check if there is a new statistics message to collect.
! 		 */
! 		if (FD_ISSET(readPipe, &rfds))
! 		{
! 			/*
! 			 * We may need to issue multiple read calls in case the buffer
! 			 * process didn't write the message in a single write, which is
! 			 * possible since it dumps its buffer bytewise. In any case, we'd
! 			 * need two reads since we don't know the message length
! 			 * initially.
! 			 */
! 			int			nread = 0;
! 			int			targetlen = sizeof(PgStat_MsgHdr);		/* initial */
! 			bool		pipeEOF = false;
  
! 			while (nread < targetlen)
  			{
! 				len = piperead(readPipe, ((char *) &msg) + nread,
! 							   targetlen - nread);
! 				if (len < 0)
! 				{
! 					if (errno == EINTR)
! 						continue;
! 					ereport(ERROR,
! 							(errcode_for_socket_access(),
! 							 errmsg("could not read from statistics collector pipe: %m")));
! 				}
! 				if (len == 0)	/* EOF on the pipe! */
  				{
! 					pipeEOF = true;
! 					break;
! 				}
! 				nread += len;
! 				if (nread == sizeof(PgStat_MsgHdr))
! 				{
! 					/* we have the header, compute actual msg length */
! 					targetlen = msg.msg_hdr.m_size;
! 					if (targetlen < (int) sizeof(PgStat_MsgHdr) ||
! 						targetlen > (int) sizeof(msg))
! 					{
! 						/*
! 						 * Bogus message length implies that we got out of
! 						 * sync with the buffer process somehow. Abort so that
! 						 * we can restart both processes.
! 						 */
! 						ereport(ERROR,
! 							  (errmsg("invalid statistics message length")));
! 					}
  				}
  			}
! 
! 			/*
! 			 * EOF on the pipe implies that the buffer process exited. Fall
! 			 * out of outer loop.
! 			 */
! 			if (pipeEOF)
! 				break;
! 
! 			/*
! 			 * Distribute the message to the specific function handling it.
! 			 */
! 			switch (msg.msg_hdr.m_type)
  			{
! 				case PGSTAT_MTYPE_DUMMY:
! 					break;
  
! 				case PGSTAT_MTYPE_BESTART:
! 					pgstat_recv_bestart((PgStat_MsgBestart *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_BETERM:
! 					pgstat_recv_beterm((PgStat_MsgBeterm *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_TABSTAT:
! 					pgstat_recv_tabstat((PgStat_MsgTabstat *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_TABPURGE:
! 					pgstat_recv_tabpurge((PgStat_MsgTabpurge *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_ACTIVITY:
! 					pgstat_recv_activity((PgStat_MsgActivity *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_DROPDB:
! 					pgstat_recv_dropdb((PgStat_MsgDropdb *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_RESETCOUNTER:
! 					pgstat_recv_resetcounter((PgStat_MsgResetcounter *) &msg,
! 											 nread);
! 					break;
  
! 				case PGSTAT_MTYPE_AUTOVAC_START:
! 					pgstat_recv_autovac((PgStat_MsgAutovacStart *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_VACUUM:
! 					pgstat_recv_vacuum((PgStat_MsgVacuum *) &msg, nread);
! 					break;
  
! 				case PGSTAT_MTYPE_ANALYZE:
! 					pgstat_recv_analyze((PgStat_MsgAnalyze *) &msg, nread);
! 					break;
  
! 				default:
! 					break;
! 			}
  
! 			/*
! 			 * Globally count messages.
! 			 */
! 			pgStatNumMessages++;
  
! 			if (need_timer)
! 			{
! 				if (setitimer(ITIMER_REAL, &timeval, NULL))
! 					ereport(ERROR,
! 						  (errmsg("unable to set statistics collector timer: %m")));
! 				need_timer = false;
! 			}
  		}
  
  		/*
  		 * Note that we do NOT check for postmaster exit inside the loop; only
  		 * EOF on the buffer pipe causes us to fall out.  This ensures we
  		 * don't exit prematurely if there are still a few messages in the
--- 1580,1704 ----
  	pgStatBeTable = (PgStat_StatBeEntry *)
  		palloc0(sizeof(PgStat_StatBeEntry) * MaxBackends);
  
  	/*
  	 * Process incoming messages and handle all the reporting stuff until
  	 * there are no more messages.
  	 */
  	for (;;)
  	{
+ 		int nread;
+ 		
  		if (need_statwrite)
  		{
! 			//pgstat_write_statsfile();
  			need_statwrite = false;
  			need_timer = true;
  		}
  
! 		if (need_timer)
  		{
! 			if (setitimer(ITIMER_REAL, &timeval, NULL))
! 				ereport(ERROR,
! 					  (errmsg("unable to set statistics collector timer: %m")));
! 			need_timer = false;
  		}
  
! 		nread = recv(pgStatSock, (char *) &msg,
! 				   sizeof(PgStat_Msg), 0);
  
! 		if (nread > 0 && is_block_mode)	/* got data */
! 		{
! 			pg_set_noblock(pgStatSock);
! 			is_block_mode = false;
! 		}
! 		else if (nread < 0)
! 		{
! 			if (errno == EAGAIN)
  			{
! 				if (!is_block_mode)
  				{
! 					/* no data, block mode */
! 					pg_set_block(pgStatSock);
! 					is_block_mode = true;
  				}
+ 				continue;
  			}
! 			else if (errno == EINTR)
  			{
! 				if (!PostmasterIsAlive(true))
! 					ereport(ERROR,
! 							(errmsg("stats collector exited: %m")));
! 				continue;
! 			}
! 			else
! 				ereport(ERROR,
! 						(errmsg("stats collector exited: %m")));
! 		}
  
! //fprintf(stderr, "nread = %d, type = %d\n", nread, msg.msg_hdr.m_type);
! if (++loops % 1000 == 0)
! 	fprintf(stderr, "loops = %d\n", loops);
  
! 		/*
! 		 * Distribute the message to the specific function handling it.
! 		 */
! 		switch (msg.msg_hdr.m_type)
! 		{
! 			case PGSTAT_MTYPE_DUMMY:
! 				break;
  
! 			case PGSTAT_MTYPE_BESTART:
! 				pgstat_recv_bestart((PgStat_MsgBestart *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_BETERM:
! 				pgstat_recv_beterm((PgStat_MsgBeterm *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_TABSTAT:
! 				pgstat_recv_tabstat((PgStat_MsgTabstat *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_TABPURGE:
! 				pgstat_recv_tabpurge((PgStat_MsgTabpurge *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_ACTIVITY:
! 				pgstat_recv_activity((PgStat_MsgActivity *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_DROPDB:
! 				pgstat_recv_dropdb((PgStat_MsgDropdb *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_RESETCOUNTER:
! 				pgstat_recv_resetcounter((PgStat_MsgResetcounter *) &msg,
! 										 nread);
! 				break;
  
! 			case PGSTAT_MTYPE_AUTOVAC_START:
! 				pgstat_recv_autovac((PgStat_MsgAutovacStart *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_VACUUM:
! 				pgstat_recv_vacuum((PgStat_MsgVacuum *) &msg, nread);
! 				break;
  
! 			case PGSTAT_MTYPE_ANALYZE:
! 				pgstat_recv_analyze((PgStat_MsgAnalyze *) &msg, nread);
! 				break;
  
! 			default:
! 				break;
  		}
  
  		/*
+ 		 * Globally count messages.
+ 		 */
+ 		pgStatNumMessages++;
+ 
+ 
+ 		/*
  		 * Note that we do NOT check for postmaster exit inside the loop; only
  		 * EOF on the buffer pipe causes us to fall out.  This ensures we
  		 * don't exit prematurely if there are still a few messages in the
***************
*** 1813,2032 ****
  }
  
  
- /* ----------
-  * pgstat_recvbuffer() -
-  *
-  *	This is the body of the separate buffering process. Its only
-  *	purpose is to receive messages from the UDP socket as fast as
-  *	possible and forward them over a pipe into the collector itself.
-  *	If the collector is slow to absorb messages, they are buffered here.
-  * ----------
-  */
- static void
- pgstat_recvbuffer(void)
- {
- 	fd_set		rfds;
- 	fd_set		wfds;
- 	struct timeval timeout;
- 	int			writePipe = pgStatPipe[1];
- 	int			maxfd;
- 	int			len;
- 	int			xfr;
- 	int			frm;
- 	PgStat_Msg	input_buffer;
- 	char	   *msgbuffer;
- 	int			msg_send = 0;	/* next send index in buffer */
- 	int			msg_recv = 0;	/* next receive index */
- 	int			msg_have = 0;	/* number of bytes stored */
- 	bool		overflow = false;
- 
- 	/*
- 	 * Identify myself via ps
- 	 */
- 	init_ps_display("stats buffer process", "", "");
- 	set_ps_display("");
- 
- 	/*
- 	 * We want to die if our child collector process does.	There are two ways
- 	 * we might notice that it has died: receive SIGCHLD, or get a write
- 	 * failure on the pipe leading to the child.  We can set SIGPIPE to kill
- 	 * us here.  Our SIGCHLD handler was already set up before we forked (must
- 	 * do it that way, else it's a race condition).
- 	 */
- 	pqsignal(SIGPIPE, SIG_DFL);
- 	PG_SETMASK(&UnBlockSig);
- 
- 	/*
- 	 * Set the write pipe to nonblock mode, so that we cannot block when the
- 	 * collector falls behind.
- 	 */
- 	if (!pg_set_noblock(writePipe))
- 		ereport(ERROR,
- 				(errcode_for_socket_access(),
- 				 errmsg("could not set statistics collector pipe to nonblocking mode: %m")));
- 
- 	/*
- 	 * Allocate the message buffer
- 	 */
- 	msgbuffer = (char *) palloc(PGSTAT_RECVBUFFERSZ);
- 
- 	/*
- 	 * Loop forever
- 	 */
- 	for (;;)
- 	{
- 		FD_ZERO(&rfds);
- 		FD_ZERO(&wfds);
- 		maxfd = -1;
- 
- 		/*
- 		 * As long as we have buffer space we add the socket to the read
- 		 * descriptor set.
- 		 */
- 		if (msg_have <= (int) (PGSTAT_RECVBUFFERSZ - sizeof(PgStat_Msg)))
- 		{
- 			FD_SET(pgStatSock, &rfds);
- 			maxfd = pgStatSock;
- 			overflow = false;
- 		}
- 		else
- 		{
- 			if (!overflow)
- 			{
- 				ereport(LOG,
- 						(errmsg("statistics buffer is full")));
- 				overflow = true;
- 			}
- 		}
- 
- 		/*
- 		 * If we have messages to write out, we add the pipe to the write
- 		 * descriptor set.
- 		 */
- 		if (msg_have > 0)
- 		{
- 			FD_SET(writePipe, &wfds);
- 			if (writePipe > maxfd)
- 				maxfd = writePipe;
- 		}
- 
- 		/*
- 		 * Wait for some work to do; but not for more than 10 seconds. (This
- 		 * determines how quickly we will shut down after an ungraceful
- 		 * postmaster termination; so it needn't be very fast.)  struct timeout
- 		 * is modified by some operating systems.
- 		 */
- 		timeout.tv_sec = 10;
- 		timeout.tv_usec = 0;
- 
- 		if (select(maxfd + 1, &rfds, &wfds, NULL, &timeout) < 0)
- 		{
- 			if (errno == EINTR)
- 				continue;
- 			ereport(ERROR,
- 					(errcode_for_socket_access(),
- 					 errmsg("select() failed in statistics buffer: %m")));
- 		}
- 
- 		/*
- 		 * If there is a message on the socket, read it and check for
- 		 * validity.
- 		 */
- 		if (FD_ISSET(pgStatSock, &rfds))
- 		{
- 			len = recv(pgStatSock, (char *) &input_buffer,
- 					   sizeof(PgStat_Msg), 0);
- 			if (len < 0)
- 				ereport(ERROR,
- 						(errcode_for_socket_access(),
- 						 errmsg("could not read statistics message: %m")));
- 
- 			/*
- 			 * We ignore messages that are smaller than our common header
- 			 */
- 			if (len < sizeof(PgStat_MsgHdr))
- 				continue;
- 
- 			/*
- 			 * The received length must match the length in the header
- 			 */
- 			if (input_buffer.msg_hdr.m_size != len)
- 				continue;
- 
- 			/*
- 			 * O.K. - we accept this message.  Copy it to the circular
- 			 * msgbuffer.
- 			 */
- 			frm = 0;
- 			while (len > 0)
- 			{
- 				xfr = PGSTAT_RECVBUFFERSZ - msg_recv;
- 				if (xfr > len)
- 					xfr = len;
- 				Assert(xfr > 0);
- 				memcpy(msgbuffer + msg_recv,
- 					   ((char *) &input_buffer) + frm,
- 					   xfr);
- 				msg_recv += xfr;
- 				if (msg_recv == PGSTAT_RECVBUFFERSZ)
- 					msg_recv = 0;
- 				msg_have += xfr;
- 				frm += xfr;
- 				len -= xfr;
- 			}
- 		}
- 
- 		/*
- 		 * If the collector is ready to receive, write some data into his
- 		 * pipe.  We may or may not be able to write all that we have.
- 		 *
- 		 * NOTE: if what we have is less than PIPE_BUF bytes but more than the
- 		 * space available in the pipe buffer, most kernels will refuse to
- 		 * write any of it, and will return EAGAIN.  This means we will
- 		 * busy-loop until the situation changes (either because the collector
- 		 * caught up, or because more data arrives so that we have more than
- 		 * PIPE_BUF bytes buffered).  This is not good, but is there any way
- 		 * around it?  We have no way to tell when the collector has caught
- 		 * up...
- 		 */
- 		if (FD_ISSET(writePipe, &wfds))
- 		{
- 			xfr = PGSTAT_RECVBUFFERSZ - msg_send;
- 			if (xfr > msg_have)
- 				xfr = msg_have;
- 			Assert(xfr > 0);
- 			len = pipewrite(writePipe, msgbuffer + msg_send, xfr);
- 			if (len < 0)
- 			{
- 				if (errno == EINTR || errno == EAGAIN)
- 					continue;	/* not enough space in pipe */
- 				ereport(ERROR,
- 						(errcode_for_socket_access(),
- 				errmsg("could not write to statistics collector pipe: %m")));
- 			}
- 			/* NB: len < xfr is okay */
- 			msg_send += len;
- 			if (msg_send == PGSTAT_RECVBUFFERSZ)
- 				msg_send = 0;
- 			msg_have -= len;
- 		}
- 
- 		/*
- 		 * Make sure we forwarded all messages before we check for postmaster
- 		 * termination.
- 		 */
- 		if (msg_have != 0 || FD_ISSET(pgStatSock, &rfds))
- 			continue;
- 
- 		/*
- 		 * If the postmaster has terminated, we die too.  (This is no longer
- 		 * the normal exit path, however.)
- 		 */
- 		if (!PostmasterIsAlive(true))
- 			exit(0);
- 	}
- }
- 
  /* SIGQUIT signal handler for buffer process */
  static void
  pgstat_exit(SIGNAL_ARGS)
--- 1726,1731 ----
***************
*** 2049,2054 ****
--- 1748,1754 ----
  	exit(0);
  }
  
+ 
  /* SIGCHLD signal handler for buffer process */
  static void
  pgstat_die(SIGNAL_ARGS)

--ELM1136421582-25820-0_--

From pgsql-performance-owner@postgresql.org  Thu Jan  5 07:30:06 2006
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Date: Thu, 05 Jan 2006 12:29:59 +0100
From: Markus Schaber <schabi@logix-tt.com>
Organization: Logical Tracking and Tracing International AG, Switzerland
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To: "Jeffrey W. Baker" <jwbaker@acm.org>
Cc: pgperf <pgsql-performance@postgresql.org>
Subject: Re: Invulnerable VACUUM process thrashing everything
References: <1135894162.2223.4.camel@toonses.gghcwest.com>
In-Reply-To: <1135894162.2223.4.camel@toonses.gghcwest.com>
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Hi, Jeffrey,

Jeffrey W. Baker wrote:
> A few WEEKS ago, the autovacuum on my instance of pg 7.4 unilaterally
> decided to VACUUM a table which has not been updated in over a year and
> is more than one terabyte on the disk.

Hmm, maybe this is the Transaction ID wraparound emerging, and VACUUM is
freezing the rows.

Did you VACUUM FREEZE the table after the last modifications?

> # kill -HUP 15308
> # kill -INT 15308
> # kill -PIPE 15308

Did you try kill -TERM?

This always cleanly ended VACUUMing backends on our machines within seconds.

> I assume that if I kill this with SIGKILL, that will bring down every
> other postgres process, so that should be avoided.  But surely there is
> a way to interrupt this.  If I had some reason to shut down the
> instance, I'd be screwed, it seems.

Yes, SIGKILL will make the postmaster shut down all running backend
instances, the same as SIGSEGV and possibly a few others.

The reason is that the postmaster assumes some internal data structure
corruption in the shared memory pages is possible on an "unclean"
backend abort, and thus quits immediately to minimize the possibility of
those corruptions to propagate to the disks.

HTH,
Markus
-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

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From: "Andy" <frum@ar-sd.net>
To: <pgsql-performance@postgresql.org>
Subject: Improving Inner Join Performance
Date: Thu, 5 Jan 2006 17:16:47 +0200
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Hi to all,=20

I have the following query:

SELECT count(*) FROM orders o
      INNER JOIN report r ON r.id_order=3Do.id
      WHERE o.id_status>3

Explaing analyze:
Aggregate  (cost=3D8941.82..8941.82 rows=3D1 width=3D0) (actual =
time=3D1003.297..1003.298 rows=3D1 loops=3D1)
  ->  Hash Join  (cost=3D3946.28..8881.72 rows=3D24041 width=3D0) =
(actual time=3D211.985..951.545 rows=3D72121 loops=3D1)
        Hash Cond: ("outer".id_order =3D "inner".id)
        ->  Seq Scan on report r  (cost=3D0.00..2952.21 rows=3D72121 =
width=3D4) (actual time=3D0.005..73.869 rows=3D72121 loops=3D1)
        ->  Hash  (cost=3D3787.57..3787.57 rows=3D24682 width=3D4) =
(actual time=3D211.855..211.855 rows=3D0 loops=3D1)
              ->  Seq Scan on orders o  (cost=3D0.00..3787.57 =
rows=3D24682 width=3D4) (actual time=3D0.047..147.170 rows=3D72121 =
loops=3D1)
                    Filter: (id_status > 3)
Total runtime: 1003.671 ms


I could use it in the following format, because I have to the moment =
only the 4,6 values for the id_status.

SELECT count(*) FROM orders o
      INNER JOIN report r ON r.id_order=3Do.id
      WHERE o.id_status IN (4,6)

Explain analyze:
Aggregate  (cost=3D5430.04..5430.04 rows=3D1 width=3D0) (actual =
time=3D1472.877..1472.877 rows=3D1 loops=3D1)
  ->  Hash Join  (cost=3D2108.22..5428.23 rows=3D720 width=3D0) (actual =
time=3D342.080..1419.775 rows=3D72121 loops=3D1)
        Hash Cond: ("outer".id_order =3D "inner".id)
        ->  Seq Scan on report r  (cost=3D0.00..2952.21 rows=3D72121 =
width=3D4) (actual time=3D0.036..106.217 rows=3D72121 loops=3D1)
        ->  Hash  (cost=3D2106.37..2106.37 rows=3D739 width=3D4) (actual =
time=3D342.011..342.011 rows=3D0 loops=3D1)
              ->  Index Scan using orders_id_status_idx, =
orders_id_status_idx on orders o  (cost=3D0.00..2106.37 rows=3D739 =
width=3D4) (actual time=3D0.131..268.397 rows=3D72121 loops=3D1)
                    Index Cond: ((id_status =3D 4) OR (id_status =3D 6))
Total runtime: 1474.356 ms

How can I improve this query's performace?? The ideea is to count all =
the values that I have in the database for the following conditions. If =
the users puts in some other search fields on the where then the query =
runs faster but in this format sometimes it takes a lot lot of =
time(sometimes even 2,3 seconds).=20

Can this be tuned somehow???

Regards,=20
Andy.


------=_NextPart_000_001A_01C6121B.CF02C500
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	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>Hi to all, </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>I have the following =
query:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>SELECT count(*) FROM orders=20
o<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INNER JOIN report r ON=20
r.id_order=3Do.id<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;WHERE=20
o.id_status&gt;3</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Explaing analyze:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Aggregate&nbsp; =
(cost=3D8941.82..8941.82 rows=3D1=20
width=3D0) (actual time=3D1003.297..1003.298 rows=3D1 =
loops=3D1)<BR>&nbsp; -&gt;&nbsp;=20
Hash Join&nbsp; (cost=3D3946.28..8881.72 rows=3D24041 width=3D0) (actual =

time=3D211.985..951.545 rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Hash Cond:=20
("outer".id_order =3D =
"inner".id)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on report r&nbsp; (cost=3D0.00..2952.21 =
rows=3D72121 width=3D4)=20
(actual time=3D0.005..73.869 rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&gt;&nbsp; =
Hash&nbsp;=20
(cost=3D3787.57..3787.57 rows=3D24682 width=3D4) (actual =
time=3D211.855..211.855 rows=3D0=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on orders o&nbsp; (cost=3D0.00..3787.57 =
rows=3D24682 width=3D4)=20
(actual time=3D0.047..147.170 rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Filter: (id_status &gt; 3)<BR>Total runtime: 1003.671 ms</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>I could use it in the following format, =
because I=20
have to the moment only the 4,6 values for the id_status.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>SELECT count(*) FROM orders=20
o<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;INNER JOIN report r ON=20
r.id_order=3Do.id<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;WHERE =
o.id_status IN=20
(4,6)</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Explain analyze:<BR>Aggregate&nbsp;=20
(cost=3D5430.04..5430.04 rows=3D1 width=3D0) (actual =
time=3D1472.877..1472.877 rows=3D1=20
loops=3D1)<BR>&nbsp; -&gt;&nbsp; Hash Join&nbsp; =
(cost=3D2108.22..5428.23 rows=3D720=20
width=3D0) (actual time=3D342.080..1419.775 rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Hash Cond:=20
("outer".id_order =3D =
"inner".id)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on report r&nbsp; (cost=3D0.00..2952.21 =
rows=3D72121 width=3D4)=20
(actual time=3D0.036..106.217 rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&gt;&nbsp; =
Hash&nbsp;=20
(cost=3D2106.37..2106.37 rows=3D739 width=3D4) (actual =
time=3D342.011..342.011 rows=3D0=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Index Scan using orders_id_status_idx, orders_id_status_idx =
on=20
orders o&nbsp; (cost=3D0.00..2106.37 rows=3D739 width=3D4) (actual =
time=3D0.131..268.397=20
rows=3D72121=20
loops=3D1)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Index Cond: ((id_status =3D 4) OR (id_status =3D 6))<BR>Total runtime: =
1474.356=20
ms<BR></DIV></FONT>
<DIV><FONT face=3DArial size=3D2>How can I improve this query's =
performace?? The=20
ideea is to count all the values that I have in the database for the =
following=20
conditions. If the users puts in some other search fields on the where =
then the=20
query runs faster but in this format sometimes it takes a lot lot of=20
time(sometimes even 2,3 seconds). </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Can this be tuned =
somehow???</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Regards, </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Andy.</DIV></FONT>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;</DIV></FONT></BODY></HTML>

------=_NextPart_000_001A_01C6121B.CF02C500--


From pgsql-performance-owner@postgresql.org  Thu Jan  5 12:44:14 2006
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Date: Thu, 05 Jan 2006 17:44:05 +0100
From: Markus Schaber <schabi@logix-tt.com>
Organization: Logical Tracking and Tracing International AG, Switzerland
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To: pgsql-performance@postgresql.org
Subject: Re: What's the best hardver for PostgreSQL 8.1?
References: <43A84D03.7090002@ritek.hu> <docq5v$24ea$1@news.hub.org>
	<200512212209.50234.caseroj@comcast.net>
	<200512212231.55100.caseroj@comcast.net>
	<20051224135042.484c6e32.frank@wiles.org>
	<6.2.5.6.0.20051224161551.01dc5d98@earthlink.net>
	<Pine.LNX.4.62.0512241350010.2807@qnivq.ynat.uz>
	<dokii5$2bba$1@news.hub.org>
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Hi, William,

William Yu wrote:

> Random write performance (small block that only writes to 1 drive):
> 1 write requires N-1 reads + N writes --> 1/2N-1 %

This is not true. Most Raid-5 engines use XOR or similar checksum
methods. As opposed to cryptographic checksums, those can be updated and
corrected incrementally.

check_new = check_old xor data_old xor data_new

So 2 reads and 2 writes are enough: read data and checksum, then adjust
the checksum via the data difference, and write data and new checksum.

And often, the old data block still is in cache, accounting to 1 read
and two writes.

HTH,
Markus
-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Thu Jan  5 15:19:58 2006
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From: Frank Wiles <frank@wiles.org>
To: "Andy" <frum@ar-sd.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Improving Inner Join Performance
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On Thu, 5 Jan 2006 17:16:47 +0200
"Andy" <frum@ar-sd.net> wrote:

> Hi to all, 
> 
> I have the following query:
> 
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=o.id
>       WHERE o.id_status>3

> How can I improve this query's performace?? The ideea is to count all
> the values that I have in the database for the following conditions.
> If the users puts in some other search fields on the where then the
> query runs faster but in this format sometimes it takes a lot lot of
> time(sometimes even 2,3 seconds). 
> 
> Can this be tuned somehow???

  Do you have an index on report.id_order ? Try creating an index for
  it if not and run a vacuum analyze on the table to see if it gets
  rid of the sequence scan in the plan.  

 ---------------------------------
   Frank Wiles <frank@wiles.org>
   http://www.wiles.org
 ---------------------------------


From pgsql-performance-owner@postgresql.org  Thu Jan  5 19:11:08 2006
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Subject: Re: Help in avoiding a query 'Warm-Up' period/shared buffer cache
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"Mark Liberman" <mliberman@mixedsignals.com> wrote
>
> First run, after a night of inactivity:
>
>                     ->  Bitmap Index Scan on 1min_events_file_id_begin_idx
> (cost=0.00..37.85 rows=3670 width=0) (actual time=313.468..313.468 
> rows=11082
> loops=1)
>                           Index Cond: (file_id = 137271)
> Total runtime: 313.643 ms
>
> Second run, after that:
>
>                     ->  Bitmap Index Scan on 1min_events_file_id_begin_idx
> (cost=0.00..37.85 rows=3670 width=0) (actual time=2.106..2.106 rows=11082
> loops=1)
>                           Index Cond: (file_id = 137271)
> Total runtime: 2.276 ms

It is clear that the first query takes longer time because of the IO time of 
index 1min_events_file_id_begin_idx (see 313.468 vs. 2.106). I am afraid 
currently there is no easy solution for this situation, unless you could 
predicate which part of relation/index your query will use, then you can 
preload or "warm-up" cache for it.

Regards,
Qingqing




From pgsql-performance-owner@postgresql.org  Thu Jan  5 20:53:26 2006
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Subject: Slow query.  Any way to speed up?
To: pgsql-performance@postgresql.org
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 <OFC6D1EDF4.8BFC181B-ON882570ED.006A2849-882570EE.0003814C@FDS.com>
From: Patrick Hatcher <PHatcher@macys.com>
Date: Thu, 5 Jan 2006 16:38:17 -0800
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Pg: 7.4.9
RH: ES v3
Quad-Xeon
16G ram

The following SQL takes 4+ mins to run.  I have indexes on all join fields
and I've tried rearranging the table orders but haven't had any luck.  I
have done the usual vacuums analyze and even vacuum FULL just to make sure
but still the same results. The ending resultset is around 169K rows which,
if I'm reading the analyze output, is more than double.   Any suggestions?

TIA
-patrick

Select gmmid, gmmname, divid, divname, feddept, fedvend,itemnumber as
mstyle,amc_week_id,
sum(tran_itm_total) as net_dollars

FROM
public.tbldetaillevel_report a2 join  cdm.cdm_ddw_tran_item a1  on
a1.item_upc = a2.upc
join public.date_dim a3 on a3.date_dim_id = a1.cal_date
where
a3.date_dim_id between '2005-10-30' and '2005-12-31'
and
a1.appl_id  in  ('MCOM','NET')
and
 a1.tran_typ_id in ('S','R')
group by 1,2,3,4,5,6,7,8
order by 1,2,3,4,5,6,7,8


GroupAggregate  (cost=1646283.56..1648297.72 rows=73242 width=65)
  ->  Sort  (cost=1646283.56..1646466.67 rows=73242 width=65)
        Sort Key: a2.gmmid, a2.gmmname, a2.divid, a2.divname, a2.feddept,
a2.fedvend, a2.itemnumber, a3.amc_week_id
        ->  Merge Join  (cost=1595839.67..1640365.47 rows=73242 width=65)
              Merge Cond: ("outer".upc = "inner".item_upc)
              ->  Index Scan using report_upc_idx on tbldetaillevel_report
a2  (cost=0.00..47236.85 rows=366234 width=58)
              ->  Sort  (cost=1595839.67..1596022.77 rows=73242 width=23)
                    Sort Key: a1.item_upc
                    ->  Hash Join  (cost=94.25..1589921.57 rows=73242
width=23)
                          Hash Cond: ("outer".cal_date =
"inner".date_dim_id)
                          ->  Seq Scan on cdm_ddw_tran_item a1
(cost=0.00..1545236.00 rows=8771781 width=23)
                                Filter: ((((appl_id)::text = 'MCOM'::text)
OR ((appl_id)::text = 'NET'::text)) AND ((tran_typ_id = 'S'::bpchar) OR
(tran_typ_id = 'R'::bpchar)))
                          ->  Hash  (cost=94.09..94.09 rows=64 width=8)
                                ->  Index Scan using date_date_idx on
date_dim a3  (cost=0.00..94.09 rows=64 width=8)
                                      Index Cond: ((date_dim_id >=
'2005-10-30'::date) AND (date_dim_id <= '2005-12-31'::date))



-- Table: tbldetaillevel_report

-- DROP TABLE tbldetaillevel_report;

CREATE TABLE tbldetaillevel_report
(
  pageid int4,
  feddept int4,
  fedvend int4,
  oz_description varchar(254),
  price_owned_retail float8,
  oz_color varchar(50),
  oz_size varchar(50),
  total_oh int4 DEFAULT 0,
  total_oo int4 DEFAULT 0,
  vendorname varchar(40),
  dunsnumber varchar(9),
  current_week int4,
  current_period int4,
  week_end date,
  varweek int4,
  varperiod int4,
  upc int8,
  itemnumber varchar(15),
  mkd_status int2,
 inforem_flag int2
)
WITH OIDS;

-- DROP INDEX report_dept_vend_idx;

CREATE INDEX report_dept_vend_idx
  ON tbldetaillevel_report
  USING btree
  (feddept, fedvend);

-- Index: report_upc_idx

-- DROP INDEX report_upc_idx;

CREATE INDEX report_upc_idx
  ON tbldetaillevel_report
  USING btree
  (upc);



-- Table: cdm.cdm_ddw_tran_item

-- DROP TABLE cdm.cdm_ddw_tran_item;

CREATE TABLE cdm.cdm_ddw_tran_item
(
  appl_xref varchar(22),
  intr_xref varchar(13),
  tran_typ_id char(1),
  cal_date date,
  cal_time time,
  tran_itm_total numeric(15,2),
  itm_qty int4,
  itm_price numeric(8,2),
  item_id int8,
  item_upc int8,
  item_pid varchar(20),
  item_desc varchar(30),
  nrf_color_name varchar(10),
  nrf_size_name varchar(10),
  dept_id int4,
  vend_id int4,
  mkstyl int4,
  item_group varchar(20),
  appl_id varchar(20),
  cost float8 DEFAULT 0,
  onhand int4 DEFAULT 0,
  onorder int4 DEFAULT 0,
  avail int4 DEFAULT 0,
  owned float8 DEFAULT 0,
  fill_store_loc int4,
  ddw_tran_key bigserial NOT NULL,
  price_type_id int2 DEFAULT 999,
  last_update date DEFAULT ('now'::text)::date,
  tran_id int8,
  tran_seq_nbr int4,
  CONSTRAINT ddw_tritm_pk PRIMARY KEY (ddw_tran_key)
)
WITHOUT OIDS;


-- Index: cdm.cdm_ddw_tran_item_applid_idx

-- DROP INDEX cdm.cdm_ddw_tran_item_applid_idx;

CREATE INDEX cdm_ddw_tran_item_applid_idx
  ON cdm.cdm_ddw_tran_item
  USING btree
  (appl_id);

-- Index: cdm.cdm_ddw_tran_item_cal_date

-- DROP INDEX cdm.cdm_ddw_tran_item_cal_date;

CREATE INDEX cdm_ddw_tran_item_cal_date
  ON cdm.cdm_ddw_tran_item
  USING btree
  (cal_date);

-- Index: cdm.cdm_ddw_tran_item_trn_type

-- DROP INDEX cdm.cdm_ddw_tran_item_trn_type;

CREATE INDEX cdm_ddw_tran_item_trn_type
  ON cdm.cdm_ddw_tran_item
  USING btree
  (tran_typ_id);

-- Index: cdm.ddw_ti_upc_idx

-- DROP INDEX cdm.ddw_ti_upc_idx;

CREATE INDEX ddw_ti_upc_idx
  ON cdm.cdm_ddw_tran_item
  USING btree
  (item_upc);

-- Index: cdm.ddw_tran_item_dept_idx

-- DROP INDEX cdm.ddw_tran_item_dept_idx;

CREATE INDEX ddw_tran_item_dept_idx
  ON cdm.cdm_ddw_tran_item
  USING btree
  (dept_id);

-- Index: cdm.ddw_trn_ittotal_idx

-- DROP INDEX cdm.ddw_trn_ittotal_idx;

CREATE INDEX ddw_trn_ittotal_idx
  ON cdm.cdm_ddw_tran_item
  USING btree
  (tran_itm_total);

-- Table: date_dim

-- DROP TABLE date_dim;

CREATE TABLE date_dim
(
  date_dim_id date NOT NULL,
  amc_date char(8),
  amc_day_nbr int2 NOT NULL,
  amc_week int2 NOT NULL,
  amc_period int2 NOT NULL,
  amc_quarter int2 NOT NULL,
  amc_season int2 NOT NULL,
  amc_year int4 NOT NULL,
  amc_period_id int4 NOT NULL,
  amc_week_id int4 NOT NULL,
  nbr_weeks_per_peri int2 NOT NULL,
  nbr_weeks_per_year int2 NOT NULL,
  calendar_day int2 NOT NULL,
  calendar_month int2 NOT NULL,
  julian_day int2 NOT NULL,
  CONSTRAINT date_dimph PRIMARY KEY (date_dim_id)
)
WITH OIDS;


-- Index: amc_weekid_idx

-- DROP INDEX amc_weekid_idx;

CREATE INDEX amc_weekid_idx
  ON date_dim
  USING btree
  (amc_week_id);

-- Index: date_date_idx

-- DROP INDEX date_date_idx;

CREATE INDEX date_date_idx
  ON date_dim
  USING btree
  (date_dim_id);


Patrick Hatcher
Development Manager  Analytics/MIO
Macys.com


From pgsql-performance-owner@postgresql.org  Thu Jan  5 21:08:23 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Ian Westmacott <ianw@intellivid.com>
Cc: Ron <rjpeace@earthlink.net>, pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging
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	<1136382865.24450.7.camel@spectre.intellivid.com>
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On Wed, Jan 04, 2006 at 11:00:38AM -0500, Ian Westmacott wrote:
> The WAL is a 2-spindle (SATA) RAID0 with its own controller (ext3).
> The tables are on a 10-spindle (SCSI) RAID50 with dual U320
> controllers (XFS).  This is overkill for writing and querying the data,
> but we need to constantly ANALYZE and VACUUM in the
> background without interrupting the inserts (the app is 24x7).  The
> databases are 4TB, so these operations can be lengthy.

How come you're using RAID50 instead of just RAID0? Or was WAL being on
RAID0 a typo?
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Thu Jan  5 22:17:33 2006
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From: Mark Liberman <mliberman@mixedsignals.com>
Organization: Mixed Signals, Inc.
To: pgsql-performance@postgresql.org
Subject: Re: Help in avoiding a query 'Warm-Up' period/shared buffer cache
Date: Thu, 5 Jan 2006 18:15:36 -0800
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On Thursday 05 January 2006 15:12, Qingqing Zhou wrote:
> "Mark Liberman" <mliberman@mixedsignals.com> wrote
>
> > First run, after a night of inactivity:
> >
> >                     ->  Bitmap Index Scan on
> > 1min_events_file_id_begin_idx (cost=0.00..37.85 rows=3670 width=0)
> > (actual time=313.468..313.468 rows=11082
> > loops=1)
> >                           Index Cond: (file_id = 137271)
> > Total runtime: 313.643 ms
> >
> > Second run, after that:
> >
> >                     ->  Bitmap Index Scan on
> > 1min_events_file_id_begin_idx (cost=0.00..37.85 rows=3670 width=0)
> > (actual time=2.106..2.106 rows=11082 loops=1)
> >                           Index Cond: (file_id = 137271)
> > Total runtime: 2.276 ms
>
> It is clear that the first query takes longer time because of the IO time
> of index 1min_events_file_id_begin_idx (see 313.468 vs. 2.106). I am afraid
> currently there is no easy solution for this situation, unless you could
> predicate which part of relation/index your query will use, then you can
> preload or "warm-up" cache for it.
>
> Regards,
> Qingqing


Thanks Qingqing, 

this actually helped me determine that the compound index, 
1min_events_file_id_begin_idx, is not the proper index to use as it is based 
on file_id and begin_time - the later of which is not involved in the where 
clause.  It is only using that index to "filter" out the listed file_id.  

Now, my follow-up question / assumption.  I am assuming that the  IO time is 
so long on that index because it has to read the entire index (for that 
file_id) into memory (because it cannot just scan the rows with a certain 
date range because we are not using begin_time in the where clause). 

But, if I replaced that compound index with the proper compound index of 
file_id / end_time, it would give similar performance results to the scan on 
1min_events_end_idx (which was < 1 ms).  E.g. the latest rows that were 
updated are more likely to be in the cache - and it is smart enough to only 
read the index rows that it needs.

Alternatively, I could create a single index on file_id (and rely upon the new 
bitmap scan capabilities in 1.2).  But, I fear that, although this will be 
smaller than the erroneous compound index on file_id / begin_time, it will 
still display the same behavior in that it will need to read all rows from 
that index for the appropriate file_id - and since the data goes back every 
minute for 60 days, that IO might be large.

Obviously, I will be testing this - but it might take a few days, as I haven't 
figure out how to simulate the "period of inactivity" to get the data flushed 
out of the cache ... so I have to run this each morning.  But, any 
confirmation / corrections to my assumptions are greatly appreciated. E.g. is 
the compound index the way to go, or the solo index on file_id?

Thanks,

Mark


From pgsql-performance-owner@postgresql.org  Thu Jan  5 22:53:22 2006
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Subject: Re: Help in avoiding a query 'Warm-Up' period/shared buffer
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On Thu, 5 Jan 2006, Mark Liberman wrote:

> Obviously, I will be testing this - but it might take a few days, as I haven't
> figure out how to simulate the "period of inactivity" to get the data flushed
> out of the cache ... so I have to run this each morning.

cat large_file >/dev/null

will probably do a pretty good job of this (especially if large_file is 
noticably larger then the amount of ram you have)

David Lang

From pgsql-performance-owner@postgresql.org  Thu Jan  5 23:06:54 2006
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"Mark Liberman" <mliberman@mixedsignals.com> wrote
>
> Now, my follow-up question / assumption.  I am assuming that the  IO time 
> is
> so long on that index because it has to read the entire index (for that
> file_id) into memory
>
> any confirmation / corrections to my assumptions are greatly appreciated. 
> E.g. is
> the compound index the way to go, or the solo index on file_id?
>

Only part of the index file is read. It is a btree index. Keep the index 
smaller but sufficient to guide your search is always good because even by 
the guidiance of the index, a heap visit to get the real data is not 
avoidable.

Regards,
Qingqing 



From pgsql-performance-owner@postgresql.org  Thu Jan  5 23:14:19 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: David Lang <dlang@invendra.net>
Cc: Mark Liberman <mliberman@mixedsignals.com>,
	pgsql-performance@postgresql.org
Subject: Re: Help in avoiding a query 'Warm-Up' period/shared buffer
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On Thu, Jan 05, 2006 at 06:50:22PM -0800, David Lang wrote:
> On Thu, 5 Jan 2006, Mark Liberman wrote:
> 
> >Obviously, I will be testing this - but it might take a few days, as I 
> >haven't
> >figure out how to simulate the "period of inactivity" to get the data 
> >flushed
> >out of the cache ... so I have to run this each morning.
> 
> cat large_file >/dev/null
> 
> will probably do a pretty good job of this (especially if large_file is 
> noticably larger then the amount of ram you have)

The following C code is much faster...

/*
 * $Id: clearmem.c,v 1.1 2003/06/29 20:41:33 decibel Exp $
 *
 * Utility to clear out a chunk of memory and zero it. Useful for flushing disk buffers
 */

int main(int argc, char *argv[]) {
    if (!calloc(atoi(argv[1]), 1024*1024)) { printf("Error allocating memory.\n"); }
}

Compile it and then pass in the number of MB of memory to allocate on
the command line.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan  6 01:08:03 2006
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To: Patrick Hatcher <PHatcher@macys.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow query. Any way to speed up? 
In-reply-to: 
 <OFC6D1EDF4.8BFC181B-ON882570ED.006A2849-882570EE.0003814C@FDS.com>
References: 
 <OFC6D1EDF4.8BFC181B-ON882570ED.006A2849-882570EE.0003814C@FDS.com>
Comments: In-reply-to Patrick Hatcher <PHatcher@macys.com>
	message dated "Thu, 05 Jan 2006 16:38:17 -0800"
Date: Fri, 06 Jan 2006 00:07:57 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Patrick Hatcher <PHatcher@macys.com> writes:
> The following SQL takes 4+ mins to run.  I have indexes on all join fields
> and I've tried rearranging the table orders but haven't had any luck.

Please show EXPLAIN ANALYZE output, not just EXPLAIN.  It's impossible
to tell whether the planner is making any wrong guesses when you can't
see the actual times/rowcounts ...

(BTW, 7.4 is looking pretty long in the tooth.)

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan  6 05:21:34 2006
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From: "Andy" <frum@ar-sd.net>
To: <pgsql-performance@postgresql.org>
References: <001d01c6120b$0d783600$0b00a8c0@forge>
	<20060105132006.19c7cd31.frank@wiles.org>
Subject: Re: Improving Inner Join Performance
Date: Fri, 6 Jan 2006 11:21:31 +0200
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Yes I have indexes an all join fields. 
The tables have around 30 columns each and around 100k rows. 
The database is vacuumed every hour.  

Andy.
----- Original Message ----- 
From: "Frank Wiles" <frank@wiles.org>
To: "Andy" <frum@ar-sd.net>
Cc: <pgsql-performance@postgresql.org>
Sent: Thursday, January 05, 2006 9:20 PM
Subject: Re: [PERFORM] Improving Inner Join Performance


> On Thu, 5 Jan 2006 17:16:47 +0200
> "Andy" <frum@ar-sd.net> wrote:
> 
>> Hi to all, 
>> 
>> I have the following query:
>> 
>> SELECT count(*) FROM orders o
>>       INNER JOIN report r ON r.id_order=o.id
>>       WHERE o.id_status>3
> 
>> How can I improve this query's performace?? The ideea is to count all
>> the values that I have in the database for the following conditions.
>> If the users puts in some other search fields on the where then the
>> query runs faster but in this format sometimes it takes a lot lot of
>> time(sometimes even 2,3 seconds). 
>> 
>> Can this be tuned somehow???
> 
>  Do you have an index on report.id_order ? Try creating an index for
>  it if not and run a vacuum analyze on the table to see if it gets
>  rid of the sequence scan in the plan.  
> 
> ---------------------------------
>   Frank Wiles <frank@wiles.org>
>   http://www.wiles.org
> ---------------------------------
> 
> 
>

From pgsql-performance-owner@postgresql.org  Fri Jan  6 05:45:23 2006
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Subject: Re: Improving Inner Join Performance
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On Jan 6, 2006, at 18:21 , Andy wrote:

> Yes I have indexes an all join fields. The tables have around 30  
> columns each and around 100k rows. The database is vacuumed every  
> hour.

Just to chime in, VACUUM != VACUUM ANALYZE. ANALYZE is what updates  
database statistics and affects query planning. VACUUM alone does not  
do this.

>>  Do you have an index on report.id_order ? Try creating an index for
>>  it if not and run a vacuum analyze on the table to see if it gets
>>  rid of the sequence scan in the plan.

Michael Glaesemann
grzm myrealbox com




From pgsql-performance-owner@postgresql.org  Fri Jan  6 05:55:46 2006
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From: "Andy" <frum@ar-sd.net>
To: "Michael Glaesemann" <grzm@myrealbox.com>
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Subject: Re: Improving Inner Join Performance
Date: Fri, 6 Jan 2006 11:54:46 +0200
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Sorry, I had to be more specific. 
VACUUM ANALYZE is performed every hour. 

Regards,
Andy.

----- Original Message ----- 
From: "Michael Glaesemann" <grzm@myrealbox.com>
To: "Andy" <frum@ar-sd.net>
Cc: <pgsql-performance@postgresql.org>
Sent: Friday, January 06, 2006 11:45 AM
Subject: Re: [PERFORM] Improving Inner Join Performance


> 
> On Jan 6, 2006, at 18:21 , Andy wrote:
> 
>> Yes I have indexes an all join fields. The tables have around 30  
>> columns each and around 100k rows. The database is vacuumed every  
>> hour.
> 
> Just to chime in, VACUUM != VACUUM ANALYZE. ANALYZE is what updates  
> database statistics and affects query planning. VACUUM alone does not  
> do this.
> 
>>>  Do you have an index on report.id_order ? Try creating an index for
>>>  it if not and run a vacuum analyze on the table to see if it gets
>>>  rid of the sequence scan in the plan.
> 
> Michael Glaesemann
> grzm myrealbox com
> 
> 
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
> 
>

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From: Pandurangan R S <pandurangan.r.s@gmail.com>
To: Andy <frum@ar-sd.net>
Subject: Re: Improving Inner Join Performance
Cc: pgsql-performance@postgresql.org
In-Reply-To: <001d01c6120b$0d783600$0b00a8c0@forge>
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> If the users puts in some other search fields on the where then the query=
 runs faster but > in this format sometimes it takes a lot lot of time(some=
times even 2,3 seconds).

Can you eloborate under what conditions which query is slower?

On 1/5/06, Andy <frum@ar-sd.net> wrote:
>
> Hi to all,
>
> I have the following query:
>
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=3Do.id
>       WHERE o.id_status>3
>
> Explaing analyze:
> Aggregate  (cost=3D8941.82..8941.82 rows=3D1 width=3D0) (actual
> time=3D1003.297..1003.298 rows=3D1 loops=3D1)
>   ->  Hash Join  (cost=3D3946.28..8881.72 rows=3D24041 width=3D0) (actual
> time=3D211.985..951.545 rows=3D72121 loops=3D1)
>         Hash Cond: ("outer".id_order =3D "inner".id)
>         ->  Seq Scan on report r  (cost=3D0.00..2952.21 rows=3D72121 widt=
h=3D4)
> (actual time=3D0.005..73.869 rows=3D72121 loops=3D1)
>         ->  Hash  (cost=3D3787.57..3787.57 rows=3D24682 width=3D4) (actua=
l
> time=3D211.855..211.855 rows=3D0 loops=3D1)
>               ->  Seq Scan on orders o  (cost=3D0.00..3787.57 rows=3D2468=
2
> width=3D4) (actual time=3D0.047..147.170 rows=3D72121 loops=3D1)
>                     Filter: (id_status > 3)
> Total runtime: 1003.671 ms
>
>
> I could use it in the following format, because I have to the moment only
> the 4,6 values for the id_status.
>
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=3Do.id
>       WHERE o.id_status IN (4,6)
>
> Explain analyze:
> Aggregate  (cost=3D5430.04..5430.04 rows=3D1 width=3D0) (actual
> time=3D1472.877..1472.877 rows=3D1 loops=3D1)
>   ->  Hash Join  (cost=3D2108.22..5428.23 rows=3D720 width=3D0) (actual
> time=3D342.080..1419.775 rows=3D72121 loops=3D1)
>         Hash Cond: ("outer".id_order =3D "inner".id)
>         ->  Seq Scan on report r  (cost=3D0.00..2952.21 rows=3D72121 widt=
h=3D4)
> (actual time=3D0.036..106.217 rows=3D72121 loops=3D1)
>         ->  Hash  (cost=3D2106.37..2106.37 rows=3D739 width=3D4) (actual
> time=3D342.011..342.011 rows=3D0 loops=3D1)
>               ->  Index Scan using orders_id_status_idx,
> orders_id_status_idx on orders o  (cost=3D0.00..2106.37 rows=3D739 width=
=3D4)
> (actual time=3D0.131..268.397 rows=3D72121 loops=3D1)
>                     Index Cond: ((id_status =3D 4) OR (id_status =3D 6))
> Total runtime: 1474.356 ms
>
> How can I improve this query's performace?? The ideea is to count all the
> values that I have in the database for the following conditions. If the
> users puts in some other search fields on the where then the query runs
> faster but in this format sometimes it takes a lot lot of time(sometimes
> even 2,3 seconds).
>
> Can this be tuned somehow???
>
> Regards,
> Andy.
>
>

From pgsql-performance-owner@postgresql.org  Fri Jan  6 06:21:29 2006
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From: "Andy" <frum@ar-sd.net>
To: "Pandurangan R S" <pandurangan.r.s@gmail.com>
Cc: <pgsql-performance@postgresql.org>
References: <001d01c6120b$0d783600$0b00a8c0@forge>
	<5e744e3d0601060156y3f68ad0dn152c946254ee9fd3@mail.gmail.com>
Subject: Re: Improving Inner Join Performance
Date: Fri, 6 Jan 2006 12:21:25 +0200
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At the moment: o.id_status>3 can have values only 4 and 6. The 6 is around
90% from the whole table. This is why seq scan is made.

Now, depending on the user input the query can have more where fields. For
example:
SELECT count(*) FROM orders o
       INNER JOIN report r ON r.id_order=o.id
       WHERE o.id_status > 3 AND r.id_zufriden=7

Aggregate  (cost=7317.15..7317.15 rows=1 width=0) (actual
time=213.418..213.419 rows=1 loops=1)
  ->  Hash Join  (cost=3139.00..7310.80 rows=2540 width=0) (actual
time=57.554..212.215 rows=1308 loops=1)
        Hash Cond: ("outer".id = "inner".id_order)
        ->  Seq Scan on orders o  (cost=0.00..3785.31 rows=72216 width=4)
(actual time=0.014..103.292 rows=72121 loops=1)
              Filter: (id_status > 3)
        ->  Hash  (cost=3132.51..3132.51 rows=2597 width=4) (actual
time=57.392..57.392 rows=0 loops=1)
              ->  Seq Scan on report r  (cost=0.00..3132.51 rows=2597
width=4) (actual time=0.019..56.220 rows=1308 loops=1)
                    Filter: (id_zufriden = 7)
Total runtime: 213.514 ms

These examples can go on and on.

If I run this query
SELECT count(*) FROM orders o
INNER JOIN report r ON r.id_order=o.id
WHERE o.id_status>3
under normal system load the average response time is between 1.3 > 2.5
seconds. Sometimes even more. If I run it rapidly a few times then it
respondes faster(that is normal I supose).

The ideea of this query is to count all the possible results that the user
can have. I use this to build pages of results.

Andy.

----- Original Message ----- 
From: "Pandurangan R S" <pandurangan.r.s@gmail.com>
To: "Andy" <frum@ar-sd.net>
Cc: <pgsql-performance@postgresql.org>
Sent: Friday, January 06, 2006 11:56 AM
Subject: Re: [PERFORM] Improving Inner Join Performance


> If the users puts in some other search fields on the where then the query
> runs faster but > in this format sometimes it takes a lot lot of
> time(sometimes even 2,3 seconds).

Can you eloborate under what conditions which query is slower?

On 1/5/06, Andy <frum@ar-sd.net> wrote:
>
> Hi to all,
>
> I have the following query:
>
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=o.id
>       WHERE o.id_status>3
>
> Explaing analyze:
> Aggregate  (cost=8941.82..8941.82 rows=1 width=0) (actual
> time=1003.297..1003.298 rows=1 loops=1)
>   ->  Hash Join  (cost=3946.28..8881.72 rows=24041 width=0) (actual
> time=211.985..951.545 rows=72121 loops=1)
>         Hash Cond: ("outer".id_order = "inner".id)
>         ->  Seq Scan on report r  (cost=0.00..2952.21 rows=72121 width=4)
> (actual time=0.005..73.869 rows=72121 loops=1)
>         ->  Hash  (cost=3787.57..3787.57 rows=24682 width=4) (actual
> time=211.855..211.855 rows=0 loops=1)
>               ->  Seq Scan on orders o  (cost=0.00..3787.57 rows=24682
> width=4) (actual time=0.047..147.170 rows=72121 loops=1)
>                     Filter: (id_status > 3)
> Total runtime: 1003.671 ms
>
>
> I could use it in the following format, because I have to the moment only
> the 4,6 values for the id_status.
>
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=o.id
>       WHERE o.id_status IN (4,6)
>
> Explain analyze:
> Aggregate  (cost=5430.04..5430.04 rows=1 width=0) (actual
> time=1472.877..1472.877 rows=1 loops=1)
>   ->  Hash Join  (cost=2108.22..5428.23 rows=720 width=0) (actual
> time=342.080..1419.775 rows=72121 loops=1)
>         Hash Cond: ("outer".id_order = "inner".id)
>         ->  Seq Scan on report r  (cost=0.00..2952.21 rows=72121 width=4)
> (actual time=0.036..106.217 rows=72121 loops=1)
>         ->  Hash  (cost=2106.37..2106.37 rows=739 width=4) (actual
> time=342.011..342.011 rows=0 loops=1)
>               ->  Index Scan using orders_id_status_idx,
> orders_id_status_idx on orders o  (cost=0.00..2106.37 rows=739 width=4)
> (actual time=0.131..268.397 rows=72121 loops=1)
>                     Index Cond: ((id_status = 4) OR (id_status = 6))
> Total runtime: 1474.356 ms
>
> How can I improve this query's performace?? The ideea is to count all the
> values that I have in the database for the following conditions. If the
> users puts in some other search fields on the where then the query runs
> faster but in this format sometimes it takes a lot lot of time(sometimes
> even 2,3 seconds).
>
> Can this be tuned somehow???
>
> Regards,
> Andy.
>
>



From pgsql-performance-owner@postgresql.org  Fri Jan  6 10:00:13 2006
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Subject: Re: improving write performance for logging
From: Ian Westmacott <ianw@intellivid.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
Cc: pgsql-performance@postgresql.org
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On Thu, 2006-01-05 at 19:08 -0600, Jim C. Nasby wrote:
> On Wed, Jan 04, 2006 at 11:00:38AM -0500, Ian Westmacott wrote:
> > The WAL is a 2-spindle (SATA) RAID0 with its own controller (ext3).
> > The tables are on a 10-spindle (SCSI) RAID50 with dual U320
> > controllers (XFS).  This is overkill for writing and querying the data,
> > but we need to constantly ANALYZE and VACUUM in the
> > background without interrupting the inserts (the app is 24x7).  The
> > databases are 4TB, so these operations can be lengthy.
> 
> How come you're using RAID50 instead of just RAID0? Or was WAL being on
> RAID0 a typo?

We use RAID50 instead of RAID0 for the tables for some fault-tolerance.
We use RAID0 for the WAL for performance.

I'm missing the implication of the question...

-- 
Ian Westmacott <ianw@intellivid.com>
Intellivid Corp.


From pgsql-performance-owner@postgresql.org  Fri Jan  6 10:04:03 2006
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Message-ID: <43BE78BE.3070508@laliluna.de>
Date: Fri, 06 Jan 2006 15:03:42 +0100
From: Sebastian Hennebrueder <usenet@laliluna.de>
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To: pgsql-performance@postgresql.org
Subject: Re: effizient query with jdbc
References: <20051215080714.03919654@malmo.geotask.ch>
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You could issue one query containing a
select uuid FROM MDM.KEYWORDS_INFO WHERE KEYWORDS_ID in (xy)
where xy is a large comma separated list of your values.

Best Regards / Viele Gr��e

Sebastian Hennebrueder

-----

http://www.laliluna.de

* Tutorials for JSP, JavaServer Faces, Struts, Hibernate and EJB
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Johannes B�hler schrieb:

> Hi, 
> I have a java.util.List of values (10000) which i wanted to use for a
> query in the where clause of an simple select statement. iterating
> over the list and and use an prepared Statement is quite slow. Is
> there a more efficient way to execute such a query.  Thanks for any
> help.  Johannes 
> ..... 
> List ids = new ArrayList(); 
> 
> .... List is filled with 10000 values ...
> 
> List uuids = new ArrayList(); 
> PreparedStatement pstat = db.prepareStatement("SELECT UUID FROM
> MDM.KEYWORDS_INFO WHERE KEYWORDS_ID = ?");  for (Iterator iter =
> ids.iterator(); iter.hasNext();) { String id = (String) iter.next();
> pstat.setString(1, id);
> rs = pstat.executeQuery();
> if (rs.next()) {
> uuids.add(rs.getString(1));
> }
> rs.close();
> } 
> ... 
> 
>
>
>---------------------------(end of broadcast)---------------------------
>TIP 3: Have you checked our extensive FAQ?
>
>               http://www.postgresql.org/docs/faq
>
>
>  
>

From pgsql-performance-owner@postgresql.org  Fri Jan  6 11:26:44 2006
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Date: Fri, 6 Jan 2006 10:26:43 -0500
From: Jaime Casanova <systemguards@gmail.com>
To: Andy <frum@ar-sd.net>
Subject: Re: Improving Inner Join Performance
Cc: Pandurangan R S <pandurangan.r.s@gmail.com>,
	pgsql-performance@postgresql.org
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On 1/6/06, Andy <frum@ar-sd.net> wrote:
> At the moment: o.id_status>3 can have values only 4 and 6. The 6 is aroun=
d
> 90% from the whole table. This is why seq scan is made.
>
given this if you make id_status > 3 you will never use an index
because you will be scanning 4 and 6 the only values in this field as
you say, and even if there were any other value 6 is 90% of whole
table, so an index for this will not be used...

> Now, depending on the user input the query can have more where fields. Fo=
r
> example:
> SELECT count(*) FROM orders o
>       INNER JOIN report r ON r.id_order=3Do.id
>       WHERE o.id_status > 3 AND r.id_zufriden=3D7
>
here the planner can be more selective, and of course the query is
faster... if you will be loading data load it all then make tests...

but because your actual data the planner will always choose to scan
the entire orders table for o.id_status > 3...

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)

From pgsql-performance-owner@postgresql.org  Sat Jan  7 14:28:11 2006
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From: Michael Stone <mstone+postgres@mathom.us>
Subject: Re: improving write performance for logging
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On Fri, Jan 06, 2006 at 09:00:06AM -0500, Ian Westmacott wrote:
>We use RAID50 instead of RAID0 for the tables for some fault-tolerance.
>We use RAID0 for the WAL for performance.
>
>I'm missing the implication of the question...

If you have the WAL on RAID 0 you have no fault tolerance, regardless of
what level you use for the tables.

Mike Stone

From pgsql-performance-owner@postgresql.org  Fri Jan  6 12:37:35 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Ian Westmacott <ianw@intellivid.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging
Message-ID: <20060106163732.GL3902@pervasive.com>
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On Fri, Jan 06, 2006 at 09:00:06AM -0500, Ian Westmacott wrote:
> On Thu, 2006-01-05 at 19:08 -0600, Jim C. Nasby wrote:
> > On Wed, Jan 04, 2006 at 11:00:38AM -0500, Ian Westmacott wrote:
> > > The WAL is a 2-spindle (SATA) RAID0 with its own controller (ext3).
> > > The tables are on a 10-spindle (SCSI) RAID50 with dual U320
> > > controllers (XFS).  This is overkill for writing and querying the data,
> > > but we need to constantly ANALYZE and VACUUM in the
> > > background without interrupting the inserts (the app is 24x7).  The
> > > databases are 4TB, so these operations can be lengthy.
> > 
> > How come you're using RAID50 instead of just RAID0? Or was WAL being on
> > RAID0 a typo?
> 
> We use RAID50 instead of RAID0 for the tables for some fault-tolerance.
> We use RAID0 for the WAL for performance.
> 
> I'm missing the implication of the question...

The problem is that if you lose WAL or the data, you've lost everything.
So you might as well use raid0 for the data if you're using it for WAL.
Or switch WAL to raid1. Actually, a really good controller *might* be
able to do a good job of raid5 for WAL. Or just use raid10.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan  6 14:55:37 2006
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In-Reply-To: <18083.1136524077@sss.pgh.pa.us>
Subject: Re: Slow query. Any way to speed up?
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
X-Mailer: Lotus Notes Release 6.5.4 March 27, 2005
Message-ID: 
 <OFD2EE5DFB.2FA6D785-ON882570EE.00679B43-882570EE.0067F414@FDS.com>
From: Patrick Hatcher <PHatcher@macys.com>
Date: Fri, 6 Jan 2006 10:55:28 -0800
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Duh sorry.  We will eventually move to 8.x, it's just a matter of finding
the time:

Explain analyze
Select gmmid, gmmname, divid, divname, feddept, fedvend,itemnumber as
mstyle,amc_week_id,
sum(tran_itm_total) as net_dollars

FROM
public.tbldetaillevel_report a2 join  cdm.cdm_ddw_tran_item a1  on
a1.item_upc = a2.upc
join public.date_dim a3 on a3.date_dim_id = a1.cal_date
where
a3.date_dim_id between '2005-10-30' and '2005-12-31'
and
a1.appl_id  in  ('MCOM','NET')
and
 a1.tran_typ_id in ('S','R')
group by 1,2,3,4,5,6,7,8
order by 1,2,3,4,5,6,7,8


GroupAggregate  (cost=1648783.47..1650793.74 rows=73101 width=65) (actual
time=744556.289..753136.278 rows=168343 loops=1)
  ->  Sort  (cost=1648783.47..1648966.22 rows=73101 width=65) (actual
time=744556.236..746634.566 rows=1185096 loops=1)
        Sort Key: a2.gmmid, a2.gmmname, a2.divid, a2.divname, a2.feddept,
a2.fedvend, a2.itemnumber, a3.amc_week_id
        ->  Merge Join  (cost=1598067.59..1642877.78 rows=73101 width=65)
(actual time=564862.772..636550.484 rows=1185096 loops=1)
              Merge Cond: ("outer".upc = "inner".item_upc)
              ->  Index Scan using report_upc_idx on tbldetaillevel_report
a2  (cost=0.00..47642.36 rows=367309 width=58) (actual
time=82.512..65458.137 rows=365989 loops=1)
              ->  Sort  (cost=1598067.59..1598250.34 rows=73100 width=23)
(actual time=564764.506..566529.796 rows=1248862 loops=1)
                    Sort Key: a1.item_upc
                    ->  Hash Join  (cost=94.25..1592161.99 rows=73100
width=23) (actual time=493500.913..548924.039 rows=1248851 loops=1)
                          Hash Cond: ("outer".cal_date =
"inner".date_dim_id)
                          ->  Seq Scan on cdm_ddw_tran_item a1
(cost=0.00..1547562.88 rows=8754773 width=23) (actual
time=14.219..535704.691 rows=10838135 loops=1)
                                Filter: ((((appl_id)::text = 'MCOM'::text)
OR ((appl_id)::text = 'NET'::text)) AND ((tran_typ_id = 'S'::bpchar) OR
(tran_typ_id = 'R'::bpchar)))
                          ->  Hash  (cost=94.09..94.09 rows=64 width=8)
(actual time=362.953..362.953 rows=0 loops=1)
                                ->  Index Scan using date_date_idx on
date_dim a3  (cost=0.00..94.09 rows=64 width=8) (actual
time=93.710..362.802 rows=63 loops=1)
                                      Index Cond: ((date_dim_id >=
'2005-10-30'::date) AND (date_dim_id <= '2005-12-31'::date))
Total runtime: 753467.847 ms


Patrick Hatcher
Development Manager  Analytics/MIO
Macys.com
415-422-1610



                                                                           
             Tom Lane                                                      
             <tgl@sss.pgh.pa.u                                             
             s>                                                         To 
                                       Patrick Hatcher                     
             01/05/06 09:07 PM         <PHatcher@macys.com>                
                                                                        cc 
                                       pgsql-performance@postgresql.org    
                                                                   Subject 
                                       Re: [PERFORM] Slow query. Any way   
                                       to speed up?                        
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Patrick Hatcher <PHatcher@macys.com> writes:
> The following SQL takes 4+ mins to run.  I have indexes on all join
fields
> and I've tried rearranging the table orders but haven't had any luck.

Please show EXPLAIN ANALYZE output, not just EXPLAIN.  It's impossible
to tell whether the planner is making any wrong guesses when you can't
see the actual times/rowcounts ...

(BTW, 7.4 is looking pretty long in the tooth.)

                                     regards, tom lane



From pgsql-performance-owner@postgresql.org  Fri Jan  6 15:03:01 2006
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Subject: Re: improving write performance for logging
From: Ian Westmacott <ianw@intellivid.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
Cc: pgsql-performance@postgresql.org
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On Fri, 2006-01-06 at 10:37 -0600, Jim C. Nasby wrote:
> The problem is that if you lose WAL or the data, you've lost everything.
> So you might as well use raid0 for the data if you're using it for WAL.
> Or switch WAL to raid1. Actually, a really good controller *might* be
> able to do a good job of raid5 for WAL. Or just use raid10.

If the WAL is lost, can you lose more than the data since the last
checkpoint?

-- 
Ian Westmacott <ianw@intellivid.com>
Intellivid Corp.


From pgsql-performance-owner@postgresql.org  Fri Jan  6 16:24:13 2006
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To: Patrick Hatcher <PHatcher@macys.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow query. Any way to speed up? 
In-reply-to: 
 <OFD2EE5DFB.2FA6D785-ON882570EE.00679B43-882570EE.0067F414@FDS.com>
References: 
 <OFD2EE5DFB.2FA6D785-ON882570EE.00679B43-882570EE.0067F414@FDS.com>
Comments: In-reply-to Patrick Hatcher <PHatcher@macys.com>
	message dated "Fri, 06 Jan 2006 10:55:28 -0800"
Date: Fri, 06 Jan 2006 15:24:09 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Patrick Hatcher <PHatcher@macys.com> writes:
>                           ->  Seq Scan on cdm_ddw_tran_item a1
> (cost=0.00..1547562.88 rows=8754773 width=23) (actual
> time=14.219..535704.691 rows=10838135 loops=1)
>                                 Filter: ((((appl_id)::text = 'MCOM'::text)
> OR ((appl_id)::text = 'NET'::text)) AND ((tran_typ_id = 'S'::bpchar) OR
> (tran_typ_id = 'R'::bpchar)))

The bulk of the time is evidently going into this step.  You didn't say
how big cdm_ddw_tran_item is, but unless it's in the billion-row range,
an indexscan isn't going to help for pulling out 10 million rows.
This may be about the best you can do :-(

If it *is* in the billion-row range, PG 8.1's bitmap indexscan facility
would probably help.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan  6 16:27:50 2006
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To: Ian Westmacott <ianw@intellivid.com>
cc: "Jim C. Nasby" <jnasby@pervasive.com>, pgsql-performance@postgresql.org
Subject: Re: improving write performance for logging 
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Comments: In-reply-to Ian Westmacott <ianw@intellivid.com>
	message dated "Fri, 06 Jan 2006 14:02:57 -0500"
Date: Fri, 06 Jan 2006 15:27:46 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Ian Westmacott <ianw@intellivid.com> writes:
> If the WAL is lost, can you lose more than the data since the last
> checkpoint?

The problem is that you might have partially-applied actions since the
last checkpoint, rendering your database inconsistent; then *all* the
data is suspect if not actually corrupt.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan  6 18:59:42 2006
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From: peter royal <peter.royal@pobox.com>
Subject: help tuning queries on large database
Date: Fri, 6 Jan 2006 17:59:24 -0500
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Howdy.

I'm running into scaling problems when testing with a 16gb (data 
+indexes) database.

I can run a query, and it returns in a few seconds. If I run it  
again, it returns in a few milliseconds. I realize this is because  
during subsequent runs, the necessary disk pages have been cached by  
the OS.

I have experimented with having all 8 disks in a single RAID0 set, a  
single RAID10 set, and currently 4 RAID0 sets of 2 disks each. There  
hasn't been an appreciable difference in the overall performance of  
my test suite (which randomly generates queries like the samples  
below as well as a few other types. this problem manifests itself on  
other queries in the test suite as well).

So, my question is, is there anything I can do to boost performance  
with what I've got, or am I in a position where the only 'fix' is  
more faster disks? I can't think of any schema/index changes that  
would help, since everything looks pretty optimal from the 'explain  
analyze' output. I'd like to get a 10x improvement when querying from  
the 'cold' state.

Thanks for any assistance. The advice from reading this list to  
getting to where I am now has been invaluable.
-peter


Configuration:

PostgreSQL 8.1.1

shared_buffers = 10000  # (It was higher, 50k, but didn't help any,  
so brought down to free ram for disk cache)
work_mem = 8196
random_page_cost = 3
effective_cache_size = 250000


Hardware:

CentOS 4.2 (Linux 2.6.9-22.0.1.ELsmp)
Areca ARC-1220 8-port PCI-E controller
8 x Hitachi Deskstar 7K80 (SATA2) (7200rpm)
2 x Opteron 242 @ 1.6ghz
3gb RAM (should be 4gb, but separate Linux issue preventing us from  
getting it to see all of it)
Tyan Thunder K8WE


RAID Layout:

4 2-disk RAID0 sets created

Each raid set is a tablespace, formatted ext3. The majority of the  
database is in the primary tablespace, and the popular object_data  
table is in its own tablespace.


Sample 1:

triple_store=# explain analyze SELECT DISTINCT O.subject AS oid FROM  
object_data O, object_tags T1, tags T2 WHERE O.type = 179 AND  
O.subject = T1.object_id AND T1.tag_id = T2.tag_id AND T2.tag =  
'transmitter\'s' LIMIT 1000;
                                                                         
         QUERY PLAN
------------------------------------------------------------------------ 
------------------------------------------------------------------------ 
-------------------------
Limit  (cost=1245.07..1245.55 rows=97 width=4) (actual  
time=3702.697..3704.665 rows=206 loops=1)
    ->  Unique  (cost=1245.07..1245.55 rows=97 width=4) (actual  
time=3702.691..3703.900 rows=206 loops=1)
          ->  Sort  (cost=1245.07..1245.31 rows=97 width=4) (actual  
time=3702.686..3703.056 rows=206 loops=1)
                Sort Key: o.subject
                ->  Nested Loop  (cost=2.82..1241.87 rows=97 width=4)  
(actual time=97.166..3701.970 rows=206 loops=1)
                      ->  Nested Loop  (cost=2.82..678.57 rows=186  
width=4) (actual time=59.903..1213.170 rows=446 loops=1)
                            ->  Index Scan using tags_tag_key on tags  
t2  (cost=0.00..5.01 rows=1 width=4) (actual time=13.139..13.143  
rows=1 loops=1)
                                  Index Cond: (tag =  
'transmitter''s'::text)
                            ->  Bitmap Heap Scan on object_tags t1   
(cost=2.82..670.65 rows=233 width=8) (actual time=46.751..1198.198  
rows=446 loops=1)
                                  Recheck Cond: (t1.tag_id =  
"outer".tag_id)
                                  ->  Bitmap Index Scan on  
object_tags_tag_id_object_id  (cost=0.00..2.82 rows=233 width=0)  
(actual time=31.571..31.571 rows=446 loops=1)
                                        Index Cond: (t1.tag_id =  
"outer".tag_id)
                      ->  Index Scan using object_data_pkey on  
object_data o  (cost=0.00..3.02 rows=1 width=4) (actual  
time=5.573..5.574 rows=0 loops=446)
                            Index Cond: (o.subject = "outer".object_id)
                            Filter: ("type" = 179)
Total runtime: 3705.166 ms
(16 rows)

triple_store=# explain analyze SELECT DISTINCT O.subject AS oid FROM  
object_data O, object_tags T1, tags T2 WHERE O.type = 179 AND  
O.subject = T1.object_id AND T1.tag_id = T2.tag_id AND T2.tag =  
'transmitter\'s' LIMIT 1000;
                                                                         
        QUERY PLAN
------------------------------------------------------------------------ 
------------------------------------------------------------------------ 
-----------------------
Limit  (cost=1245.07..1245.55 rows=97 width=4) (actual  
time=11.037..12.923 rows=206 loops=1)
    ->  Unique  (cost=1245.07..1245.55 rows=97 width=4) (actual  
time=11.031..12.190 rows=206 loops=1)
          ->  Sort  (cost=1245.07..1245.31 rows=97 width=4) (actual  
time=11.027..11.396 rows=206 loops=1)
                Sort Key: o.subject
                ->  Nested Loop  (cost=2.82..1241.87 rows=97 width=4)  
(actual time=0.430..10.461 rows=206 loops=1)
                      ->  Nested Loop  (cost=2.82..678.57 rows=186  
width=4) (actual time=0.381..3.479 rows=446 loops=1)
                            ->  Index Scan using tags_tag_key on tags  
t2  (cost=0.00..5.01 rows=1 width=4) (actual time=0.058..0.061 rows=1  
loops=1)
                                  Index Cond: (tag =  
'transmitter''s'::text)
                            ->  Bitmap Heap Scan on object_tags t1   
(cost=2.82..670.65 rows=233 width=8) (actual time=0.310..1.730  
rows=446 loops=1)
                                  Recheck Cond: (t1.tag_id =  
"outer".tag_id)
                                  ->  Bitmap Index Scan on  
object_tags_tag_id_object_id  (cost=0.00..2.82 rows=233 width=0)  
(actual time=0.199..0.199 rows=446 loops=1)
                                        Index Cond: (t1.tag_id =  
"outer".tag_id)
                      ->  Index Scan using object_data_pkey on  
object_data o  (cost=0.00..3.02 rows=1 width=4) (actual  
time=0.009..0.010 rows=0 loops=446)
                            Index Cond: (o.subject = "outer".object_id)
                            Filter: ("type" = 179)
Total runtime: 13.411 ms
(16 rows)

triple_store=#


Sample 2:

triple_store=# explain analyze SELECT DISTINCT O.subject AS oid FROM  
object_data O, object_tags T1, tags T2 WHERE O.type = 93 AND  
O.subject = T1.object_id AND T1.tag_id = T2.tag_id AND T2.tag =  
'current' LIMIT 1000;
                                                                         
         QUERY PLAN
------------------------------------------------------------------------ 
------------------------------------------------------------------------ 
-------------------------
Limit  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=6411.409..6411.409 rows=0 loops=1)
    ->  Unique  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=6411.405..6411.405 rows=0 loops=1)
          ->  Sort  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=6411.400..6411.400 rows=0 loops=1)
                Sort Key: o.subject
                ->  Nested Loop  (cost=2.82..1241.87 rows=1 width=4)  
(actual time=6411.386..6411.386 rows=0 loops=1)
                      ->  Nested Loop  (cost=2.82..678.57 rows=186  
width=4) (actual time=46.045..2229.978 rows=446 loops=1)
                            ->  Index Scan using tags_tag_key on tags  
t2  (cost=0.00..5.01 rows=1 width=4) (actual time=11.798..11.802  
rows=1 loops=1)
                                  Index Cond: (tag = 'current'::text)
                            ->  Bitmap Heap Scan on object_tags t1   
(cost=2.82..670.65 rows=233 width=8) (actual time=34.222..2216.321  
rows=446 loops=1)
                                  Recheck Cond: (t1.tag_id =  
"outer".tag_id)
                                  ->  Bitmap Index Scan on  
object_tags_tag_id_object_id  (cost=0.00..2.82 rows=233 width=0)  
(actual time=25.523..25.523 rows=446 loops=1)
                                        Index Cond: (t1.tag_id =  
"outer".tag_id)
                      ->  Index Scan using object_data_pkey on  
object_data o  (cost=0.00..3.02 rows=1 width=4) (actual  
time=9.370..9.370 rows=0 loops=446)
                            Index Cond: (o.subject = "outer".object_id)
                            Filter: ("type" = 93)
Total runtime: 6411.516 ms
(16 rows)

triple_store=# explain analyze SELECT DISTINCT O.subject AS oid FROM  
object_data O, object_tags T1, tags T2 WHERE O.type = 93 AND  
O.subject = T1.object_id AND T1.tag_id = T2.tag_id AND T2.tag =  
'current' LIMIT 1000;
                                                                         
        QUERY PLAN
------------------------------------------------------------------------ 
------------------------------------------------------------------------ 
-----------------------
Limit  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=9.437..9.437 rows=0 loops=1)
    ->  Unique  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=9.431..9.431 rows=0 loops=1)
          ->  Sort  (cost=1241.88..1241.88 rows=1 width=4) (actual  
time=9.426..9.426 rows=0 loops=1)
                Sort Key: o.subject
                ->  Nested Loop  (cost=2.82..1241.87 rows=1 width=4)  
(actual time=9.414..9.414 rows=0 loops=1)
                      ->  Nested Loop  (cost=2.82..678.57 rows=186  
width=4) (actual time=0.347..3.477 rows=446 loops=1)
                            ->  Index Scan using tags_tag_key on tags  
t2  (cost=0.00..5.01 rows=1 width=4) (actual time=0.039..0.042 rows=1  
loops=1)
                                  Index Cond: (tag = 'current'::text)
                            ->  Bitmap Heap Scan on object_tags t1   
(cost=2.82..670.65 rows=233 width=8) (actual time=0.297..1.688  
rows=446 loops=1)
                                  Recheck Cond: (t1.tag_id =  
"outer".tag_id)
                                  ->  Bitmap Index Scan on  
object_tags_tag_id_object_id  (cost=0.00..2.82 rows=233 width=0)  
(actual time=0.185..0.185 rows=446 loops=1)
                                        Index Cond: (t1.tag_id =  
"outer".tag_id)
                      ->  Index Scan using object_data_pkey on  
object_data o  (cost=0.00..3.02 rows=1 width=4) (actual  
time=0.009..0.009 rows=0 loops=446)
                            Index Cond: (o.subject = "outer".object_id)
                            Filter: ("type" = 93)
Total runtime: 9.538 ms
(16 rows)

triple_store=#


Schema:

triple_store=# \d object_data
                Table "public.object_data"
     Column     |            Type             | Modifiers
---------------+-----------------------------+-----------
subject       | integer                     | not null
type          | integer                     | not null
owned_by      | integer                     | not null
created_by    | integer                     | not null
created       | timestamp without time zone | not null
last_modified | timestamp without time zone | not null
label         | text                        |
Indexes:
     "object_data_pkey" PRIMARY KEY, btree (subject)
     "object_data_type_created_by" btree ("type", created_by)
     "object_data_type_owned_by" btree ("type", owned_by)
Foreign-key constraints:
     "object_data_created_by_fkey" FOREIGN KEY (created_by)  
REFERENCES objects(object_id) DEFERRABLE INITIALLY DEFERRED
     "object_data_owned_by_fkey" FOREIGN KEY (owned_by) REFERENCES  
objects(object_id) DEFERRABLE INITIALLY DEFERRED
     "object_data_type_fkey" FOREIGN KEY ("type") REFERENCES objects 
(object_id) DEFERRABLE INITIALLY DEFERRED
Tablespace: "alt_2"

triple_store=# \d object_tags
    Table "public.object_tags"
   Column   |  Type   | Modifiers
-----------+---------+-----------
object_id | integer | not null
tag_id    | integer | not null
Indexes:
     "object_tags_pkey" PRIMARY KEY, btree (object_id, tag_id)
     "object_tags_tag_id" btree (tag_id)
     "object_tags_tag_id_object_id" btree (tag_id, object_id)
Foreign-key constraints:
     "object_tags_object_id_fkey" FOREIGN KEY (object_id) REFERENCES  
objects(object_id) DEFERRABLE INITIALLY DEFERRED
     "object_tags_tag_id_fkey" FOREIGN KEY (tag_id) REFERENCES tags 
(tag_id) DEFERRABLE INITIALLY DEFERRED

triple_store=# \d tags
                            Table "public.tags"
Column |  Type   |                       Modifiers
--------+--------- 
+-------------------------------------------------------
tag_id | integer | not null default nextval('tags_tag_id_seq'::regclass)
tag    | text    | not null
Indexes:
     "tags_pkey" PRIMARY KEY, btree (tag_id)
     "tags_tag_key" UNIQUE, btree (tag)

-- 
(peter.royal|osi)@pobox.com - http://fotap.org/~osi


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From pgsql-performance-owner@postgresql.org  Fri Jan  6 19:48:03 2006
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To: peter royal <peter.royal@pobox.com>
cc: pgsql-performance@postgresql.org
Subject: Re: help tuning queries on large database 
In-reply-to: <FC9B7CC4-F469-4BF5-8862-332E6C26BEA5@pobox.com> 
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Comments: In-reply-to peter royal <peter.royal@pobox.com>
	message dated "Fri, 06 Jan 2006 17:59:24 -0500"
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peter royal <peter.royal@pobox.com> writes:
> So, my question is, is there anything I can do to boost performance  
> with what I've got, or am I in a position where the only 'fix' is  
> more faster disks? I can't think of any schema/index changes that  
> would help, since everything looks pretty optimal from the 'explain  
> analyze' output. I'd like to get a 10x improvement when querying from  
> the 'cold' state.

I don't think you have any hope of improving the "cold" state much.
The right way to think about this is not to be in the "cold" state.
Check your kernel parameters and make sure it's not set to limit
the amount of memory used for cache (I'm not actually sure if there
is such a limit on Linux, but there definitely is on some other Unixen).
Look around and see if you can reduce the memory used by processes,
or even better, offload non-database tasks to other machines.

Basically you need to get as much of the database as you can to stay
in disk cache.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan  6 21:09:35 2006
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From pgsql-performance-owner@postgresql.org  Fri Jan  6 21:21:48 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
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Subject: Re: help tuning queries on large database
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On Fri, 6 Jan 2006, Tom Lane wrote:

> Date: Fri, 06 Jan 2006 18:47:55 -0500
> From: Tom Lane <tgl@sss.pgh.pa.us>
> To: peter royal <peter.royal@pobox.com>
> Cc: pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] help tuning queries on large database
> 
> peter royal <peter.royal@pobox.com> writes:
>> So, my question is, is there anything I can do to boost performance
>> with what I've got, or am I in a position where the only 'fix' is
>> more faster disks? I can't think of any schema/index changes that
>> would help, since everything looks pretty optimal from the 'explain
>> analyze' output. I'd like to get a 10x improvement when querying from
>> the 'cold' state.
>
> I don't think you have any hope of improving the "cold" state much.
> The right way to think about this is not to be in the "cold" state.
> Check your kernel parameters and make sure it's not set to limit
> the amount of memory used for cache (I'm not actually sure if there
> is such a limit on Linux, but there definitely is on some other Unixen).

Linux doesn't have any ability to limit the amount of memory used for 
caching (there are periodicly requests for such a feature)

David Lang

> Look around and see if you can reduce the memory used by processes,
> or even better, offload non-database tasks to other machines.
>
> Basically you need to get as much of the database as you can to stay
> in disk cache.
>
> 			regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>

From pgsql-hackers-owner@postgresql.org  Sun Jan  8 12:49:29 2006
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To: Hannu Krosing <hannu@skype.net>
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	Qingqing Zhou <zhouqq@cs.toronto.edu>,  pgsql-hackers@postgresql.org
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Hannu Krosing <hannu@skype.net> writes:

> Interestingly I use pg_stat_activity view to watch for stuck backends,
> "stuck" in the sense that they have not noticed when client want away
> and are now waitin the TCP timeout to happen. I query for backends which
> have been in "<IDLE>" state for longer than XX seconds. I guess that at
> least some kind of indication for this should be available.

You mean like the tcp_keepalives_idle option?

http://www.postgresql.org/docs/8.1/interactive/runtime-config-connection.html#GUC-TCP-KEEPALIVES-IDLE

-- 
greg


From pgsql-performance-owner@postgresql.org  Sat Jan 14 01:50:07 2006
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From: vimal.gupta@gmail.com
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We have to inserts a records(15000- 20000) into a table which also
contains (15000-20000) records, then after insertion, we have to delete
the records according to a business rule.
Above process is taking place in a transaction and we are using batches
of 128 to insert records.
Everything works fine on QA environment but somehow after inserts,
delete query hangs in production environment. Delete query has some
joins with other table and a self join. There is no exception as we
have done enough exception handling. It simply hangs with no trace in
application logs.

When I do "ps aux" , I see
postgres  5294 41.3  2.4 270120 38092 pts/4  R    10:41  52:56
postgres: nuuser nm 127.0.0.1 DELETE

Postgres 7.3.4 on Linux..

Thanks for any help..

Vimal


From pgsql-performance-owner@postgresql.org  Sun Jan  8 14:42:44 2006
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Date: Sun, 08 Jan 2006 10:42:31 -0800
Subject: Re: help tuning queries on large database
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "peter royal" <peter.royal@pobox.com>,
	pgsql-performance@postgresql.org
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Peter,

On 1/6/06 2:59 PM, "peter royal" <peter.royal@pobox.com> wrote:

> I have experimented with having all 8 disks in a single RAID0 set, a
> single RAID10 set, and currently 4 RAID0 sets of 2 disks each. There
> hasn't been an appreciable difference in the overall performance of
> my test suite (which randomly generates queries like the samples
> below as well as a few other types. this problem manifests itself on
> other queries in the test suite as well).

Have you tested the underlying filesystem for it's performance?  Run this:
  time bash -c 'dd if=/dev/zero of=/my_file_system/bigfile bs=8k
count=<your_memory_size_in_GB * 250000> && sync'

Then run this:
  time dd if=/my_file_system/bigfile bs=8k of=/dev/null

And report the times here please.  With your 8 disks in any of the RAID0
configurations you describe, you should be getting 480MB/s.  In the RAID10
configuration you should get 240.

Note that ext3 will not go faster than about 300MB/s in our experience.  You
should use xfs, which will run *much* faster.

You should also experiment with using larger readahead, which you can
implement like this:
  blockdev --setra 16384 /dev/<my_block_device>

E.g. "blockdev --setra 16384 /dev/sda"

This will set the readahead of Linux block device reads to 16MB.  Using
3Ware's newest controllers we have seen 500MB/s + on 8 disk drives in RAID0
on CentOS 4.1 with xfs.  Note that you will need to run the "CentOS
unsupported kernel" to get xfs.

> So, my question is, is there anything I can do to boost performance
> with what I've got, or am I in a position where the only 'fix' is
> more faster disks? I can't think of any schema/index changes that
> would help, since everything looks pretty optimal from the 'explain
> analyze' output. I'd like to get a 10x improvement when querying from
> the 'cold' state.

 From what you describe, one of these is likely:
- hardware isn't configured properly or a driver problem.
- you need to use xfs and tune your Linux readahead

- Luke



From pgsql-performance-owner@postgresql.org  Sun Jan  8 17:35:20 2006
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Subject: Re: help tuning queries on large database
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I'll second all of Luke Lonergan's comments and add these.

You should be able to increase both "cold" and "warm" performance (as 
well as data integrity.  read below.) considerably.
Ron

At 05:59 PM 1/6/2006, peter royal wrote:
>Howdy.
>
>I'm running into scaling problems when testing with a 16gb (data 
>+indexes) database.
>
>I can run a query, and it returns in a few seconds. If I run it
>again, it returns in a few milliseconds. I realize this is because
>during subsequent runs, the necessary disk pages have been cached by
>the OS.
>
>I have experimented with having all 8 disks in a single RAID0 set, a
>single RAID10 set, and currently 4 RAID0 sets of 2 disks each. There
>hasn't been an appreciable difference in the overall performance of
>my test suite (which randomly generates queries like the samples
>below as well as a few other types. this problem manifests itself on
>other queries in the test suite as well).
>
>So, my question is, is there anything I can do to boost performance
>with what I've got, or am I in a position where the only 'fix' is
>more faster disks? I can't think of any schema/index changes that
>would help, since everything looks pretty optimal from the 'explain
>analyze' output. I'd like to get a 10x improvement when querying from
>the 'cold' state.
>
>Thanks for any assistance. The advice from reading this list to
>getting to where I am now has been invaluable.
>-peter
>
>
>Configuration:
>
>PostgreSQL 8.1.1
>
>shared_buffers = 10000  # (It was higher, 50k, but didn't help any,
>so brought down to free ram for disk cache)
>work_mem = 8196
>random_page_cost = 3
>effective_cache_size = 250000
>
>
>Hardware:
>
>CentOS 4.2 (Linux 2.6.9-22.0.1.ELsmp)

Upgrade your kernel to at least  2.6.12
There's a known issue with earlier versions of the 2.6.x kernel and 
64b CPUs like the Opteron.  See kernel.org for details.

>Areca ARC-1220 8-port PCI-E controller

Make sure you have 1GB or 2GB of cache.  Get the battery backup and 
set the cache for write back rather than write through.

>8 x Hitachi Deskstar 7K80 (SATA2) (7200rpm)
>2 x Opteron 242 @ 1.6ghz
>3gb RAM (should be 4gb, but separate Linux issue preventing us from
>getting it to see all of it)
>Tyan Thunder K8WE
The K8WE has 8 DIMM slots.  That should be good for 16 or 32 GB of 
RAM (Depending on whether the mainboard recognizes 4GB DIMMs or 
not.  Ask Tyan about the latest K8WE firmare.).  If nothing else, 1GB 
DIMMs are now so cheap that you should have no problems having 8GB on the K8WE.

A 2.6.12 or later based Linux distro should have NO problems using 
more than 4GB or RAM.

Among the other tricks having lots of RAM allows:
If some of your tables are Read Only or VERY rarely written to, you 
can preload them at boot time and make them RAM resident using the 
/etc/tmpfs trick.

In addition there is at least one company making a cheap battery 
backed PCI-X card that can hold up to 4GB of RAM and pretend to be a 
small HD to the OS.  I don't remember any names at the moment, but 
there have been posts here and at storage.review.com on such products.


>RAID Layout:
>
>4 2-disk RAID0 sets created
You do know that a RAID 0 set provides _worse_ data protection than a 
single HD?  Don't use RAID 0 for any data you want kept reliably.

With 8 HDs, the best config is probably
1 2HD RAID 1 + 1 6HD RAID 10  or
2 4HD RAID 10's

It is certainly true that once you have done everything you can with 
RAM, the next set of HW optimizations is to add HDs.  The more the 
better up to a the limits of your available PCI-X bandwidth.

In short, a 2nd RAID fully populated controller is not unreasonable.



From pgsql-performance-owner@postgresql.org  Mon Jan  9 03:56:57 2006
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To: "Frank Wiles" <frank@wiles.org>
Cc: <pgsql-performance@postgresql.org>
References: 
 <001d01c6120b$0d783600$0b00a8c0@forge><20060105132006.19c7cd31.frank@wiles.org><001601c61297$20da58e0$0b00a8c0@forge>
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Subject: Re: Improving Inner Join Performance
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shared_buffers =3D 10240
effective_cache_size =3D 64000
RAM on server: 1Gb.=20

Andy.

----- Original Message -----=20

From: "Frank Wiles" <frank@wiles.org>
To: "Andy" <frum@ar-sd.net>
Sent: Friday, January 06, 2006 7:12 PM
Subject: Re: [PERFORM] Improving Inner Join Performance


> On Fri, 6 Jan 2006 09:59:30 +0200
> "Andy" <frum@ar-sd.net> wrote:
>=20
>> Yes I have indexes an all join fields.=20
>> The tables have around 30 columns each and around 100k rows.=20
>> The database is vacuumed every hour. =20
>=20
>  What are you settings for:=20
>=20
>  shared_buffers=20
>  effective_cache_size
>=20
>  And how much RAM do you have in the server?=20
>=20
> ---------------------------------
>   Frank Wiles <frank@wiles.org>
>   http://www.wiles.org
> ---------------------------------
>=20
>=20
>
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charset=3Diso-8859-1">
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<STYLE></STYLE>
</HEAD>
<BODY>
<P><FONT face=3DArial size=3D2>shared_buffers =3D =
10240<BR>effective_cache_size =3D=20
64000<BR></FONT><FONT face=3DArial size=3D2>RAM on server: 1Gb. =
</FONT></P>
<P><FONT face=3DArial size=3D2>Andy.</FONT></P>
<P><FONT face=3DArial size=3D2>----- Original Message ----- </FONT></P>
<DIV>
<DIV><FONT face=3DArial size=3D2>From: "Frank Wiles" &lt;</FONT><A=20
href=3D"mailto:frank@wiles.org"><FONT face=3DArial=20
size=3D2>frank@wiles.org</FONT></A><FONT face=3DArial =
size=3D2>&gt;</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>To: "Andy" &lt;</FONT><A=20
href=3D"mailto:frum@ar-sd.net"><FONT face=3DArial=20
size=3D2>frum@ar-sd.net</FONT></A><FONT face=3DArial =
size=3D2>&gt;</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Sent: Friday, January 06, 2006 7:12 =
PM</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Subject: Re: [PERFORM] Improving Inner =
Join=20
Performance</FONT></DIV></DIV>
<DIV><FONT face=3DArial><BR><FONT size=3D2></FONT></FONT></DIV><FONT =
face=3DArial=20
size=3D2>&gt; On Fri, 6 Jan 2006 09:59:30 +0200<BR>&gt; "Andy" =
&lt;</FONT><A=20
href=3D"mailto:frum@ar-sd.net"><FONT face=3DArial=20
size=3D2>frum@ar-sd.net</FONT></A><FONT face=3DArial size=3D2>&gt; =
wrote:<BR>&gt;=20
<BR>&gt;&gt; Yes I have indexes an all join fields. <BR>&gt;&gt; The =
tables have=20
around 30 columns each and around 100k rows. <BR>&gt;&gt; The database =
is=20
vacuumed every hour.&nbsp; <BR>&gt; <BR>&gt;&nbsp; What are you settings =
for:=20
<BR>&gt; <BR>&gt;&nbsp; shared_buffers <BR>&gt;&nbsp;=20
effective_cache_size<BR>&gt; <BR>&gt;&nbsp; And how much RAM do you have =
in the=20
server? <BR>&gt;=20
<BR>&gt;&nbsp;---------------------------------<BR>&gt;&nbsp;&nbsp; =
Frank Wiles=20
&lt;</FONT><A href=3D"mailto:frank@wiles.org"><FONT face=3DArial=20
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href=3D"http://www.wiles.org"><FONT=20
face=3DArial size=3D2>http://www.wiles.org</FONT></A><BR><FONT =
face=3DArial=20
size=3D2>&gt;&nbsp;---------------------------------<BR>&gt; <BR>&gt;=20
<BR>&gt;</FONT></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Mon Jan  9 06:58:25 2006
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Subject: [PERFORMANCE] Beetwen text and varchar field
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Hello

what is the best for a char field with less than 1000 characters?
a text field or a varchar(1000)

thanks


From pgsql-performance-owner@postgresql.org  Mon Jan  9 07:49:40 2006
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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: TNO <tnodev@free.fr>
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Beetwen text and varchar field
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On Mon, Jan 09, 2006 at 11:58:19AM +0100, TNO wrote:
> what is the best for a char field with less than 1000 characters?
> a text field or a varchar(1000)

They will be equivalent. text and varchar are the same type internally -- the
only differences are that varchar can have a length (but does not need one),
and that some casts are only defined for text.

If there's really a natural thousand-character limit to the data in question,
use varchar(1000); if not, use text or varchar, whatever you'd like.

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Mon Jan  9 09:51:21 2006
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Hello gentlemen,

Although this is my first post on the list, I am a fairly experienced PostgreSQL 
programmer. I am writing an ERP application suite using PostgreSQL as the 
preferred DBMS. Let me state that the SQL DDL is automatically generated by a 
CASE tool from an ER model. The generated schema contains the appropriate 
primary key and foreign key constraints, as defined by the original ER model, as 
well as "reverse indexes" on foreign keys, allowing (in theory) rapid backward 
navigation of foreign keys in joins.

Let me show a sample join of two tables in the database schema. The information 
provided is quite extensive. I'm sorry for that, but I think it is better to 
provide the list with all the relevant information.

Package: postgresql-7.4
Priority: optional
Section: misc
Installed-Size: 7860
Maintainer: Martin Pitt <mpitt@debian.org>
Architecture: i386
Version: 1:7.4.9-2



                                            Table "public.articolo"
          Column          |            Type             | 
Modifiers
-------------------------+-----------------------------+-----------------------------------------------------
  bigoid                  | bigint                      | not null default 
nextval('object_bigoid_seq'::text)
  metadata                | text                        |
  finalized               | timestamp without time zone |
  xdbs_created            | timestamp without time zone | default now()
  xdbs_modified           | timestamp without time zone |
  id_ente                 | text                        | not null
  barcode                 | text                        |
  tipo                    | text                        |
  id_produttore           | text                        | not null
  id_articolo             | text                        | not null
  venditore_id_ente       | text                        |
  id_prodotto             | text                        |
  aggregato_id_ente       | text                        |
  aggregato_id_produttore | text                        |
  aggregato_id_articolo   | text                        |
  descr                   | text                        |
  url                     | text                        |
  datasheet               | text                        |
  scheda_sicurezza        | text                        |
  peso                    | numeric                     |
  lunghezza               | numeric                     |
  larghezza               | numeric                     |
  altezza                 | numeric                     |
  volume                  | numeric                     |
  max_strati              | numeric                     |
  um                      | text                        |
Indexes:
     "articolo_pkey" primary key, btree (id_ente, id_produttore, id_articolo)
     "articolo_unique_barcode_index" unique, btree (barcode)
     "articolo_modified_index" btree (xdbs_modified)
Foreign-key constraints:
     "$4" FOREIGN KEY (um) REFERENCES um(um) DEFERRABLE INITIALLY DEFERRED
     "$3" FOREIGN KEY (aggregato_id_ente, aggregato_id_produttore, 
aggregato_id_articolo) REFERENCES articolo(id_ente, id_produttore, id_articolo) 
DEFERRABLE INITIALLY DEFERRED
     "$2" FOREIGN KEY (venditore_id_ente, id_prodotto) REFERENCES 
prodotto(venditore_id_ente, id_prodotto) DEFERRABLE INITIALLY DEFERRED
     "$1" FOREIGN KEY (id_ente) REFERENCES ente(id_ente) DEFERRABLE INITIALLY 
DEFERRED
Rules:
     articolo_delete_rule AS ON DELETE TO articolo DO INSERT INTO articolo_trash 
(id_ente, id_produttore, id_articolo, venditore_id_ente, id_prodotto, 
aggregato_id_ente, aggregato_id_produttore, aggregato_id_articolo, descr, url, 
datasheet, scheda_sicurezza, peso, lunghezza, larghezza, altezza, volume, 
max_strati, um, barcode, tipo, bigoid, metadata, finalized, xdbs_created, 
xdbs_modified) VALUES (old.id_ente, old.id_produttore, old.id_articolo, 
old.venditore_id_ente, old.id_prodotto, old.aggregato_id_ente, 
old.aggregato_id_produttore, old.aggregato_id_articolo, old.descr, old.url, 
old.datasheet, old.scheda_sicurezza, old.peso, old.lunghezza, old.larghezza, 
old.altezza, old.volume, old.max_strati, old.um, old.barcode, old.tipo, 
old.bigoid, old.metadata, old.finalized, old.xdbs_created, old.xdbs_modified)
     articolo_update_rule AS ON UPDATE TO articolo WHERE 
((new.xdbs_modified)::timestamp with time zone <> now()) DO INSERT INTO 
articolo_trash (id_ente, id_produttore, id_articolo, venditore_id_ente, 
id_prodotto, aggregato_id_ente, aggregato_id_produttore, aggregato_id_articolo, 
descr, url, datasheet, scheda_sicurezza, peso, lunghezza, larghezza, altezza, 
volume, max_strati, um, barcode, tipo, bigoid, metadata, finalized, 
xdbs_created, xdbs_modified) VALUES (old.id_ente, old.id_produttore, 
old.id_articolo, old.venditore_id_ente, old.id_prodotto, old.aggregato_id_ente, 
old.aggregato_id_produttore, old.aggregato_id_articolo, old.descr, old.url, 
old.datasheet, old.scheda_sicurezza, old.peso, old.lunghezza, old.larghezza, 
old.altezza, old.volume, old.max_strati, old.um, old.barcode, old.tipo, 
old.bigoid, old.metadata, old.finalized, old.xdbs_created, old.xdbs_modified)
Triggers:
     articolo_update_trigger BEFORE UPDATE ON articolo FOR EACH ROW EXECUTE 
PROCEDURE xdbs_update_trigger()
Inherits: object,
           barcode


                                      Table "public.ubicazione"
     Column     |            Type             |                      Modifiers
---------------+-----------------------------+-----------------------------------------------------
  bigoid        | bigint                      | not null default 
nextval('object_bigoid_seq'::text)
  metadata      | text                        |
  finalized     | timestamp without time zone |
  xdbs_created  | timestamp without time zone | default now()
  xdbs_modified | timestamp without time zone |
  id_ente       | text                        | not null
  barcode       | text                        |
  tipo          | text                        |
  id_magazzino  | text                        | not null
  id_settore    | text                        | not null
  id_area       | text                        | not null
  id_ubicazione | text                        | not null
  flavor        | text                        |
  peso_max      | numeric                     |
  lunghezza     | numeric                     |
  larghezza     | numeric                     |
  altezza       | numeric                     |
  volume_max    | numeric                     |
  inventario    | integer                     | default 0
  allarme       | text                        |
  manutenzione  | text                        |
  id_produttore | text                        |
  id_articolo   | text                        |
  quantita      | numeric                     |
  in_prelievo   | numeric                     |
  in_deposito   | numeric                     |
  lotto         | text                        |
  scadenza      | date                        |
Indexes:
     "ubicazione_pkey" primary key, btree (id_ente, id_magazzino, id_settore, 
id_area, id_ubicazione)
     "ubicazione_id_ubicazione_key" unique, btree (id_ubicazione)
     "ubicazione_fkey_articolo" btree (id_ente, id_produttore, id_articolo)
     "ubicazione_modified_index" btree (xdbs_modified)
Foreign-key constraints:
     "$5" FOREIGN KEY (id_ente, id_produttore, id_articolo) REFERENCES 
articolo(id_ente, id_produttore, id_articolo) DEFERRABLE INITIALLY DEFERRED
     "$4" FOREIGN KEY (manutenzione) REFERENCES manutenzione(manutenzione) 
DEFERRABLE INITIALLY DEFERRED
     "$3" FOREIGN KEY (allarme) REFERENCES allarme(allarme) DEFERRABLE INITIALLY 
DEFERRED
     "$2" FOREIGN KEY (flavor) REFERENCES flavor(flavor) DEFERRABLE INITIALLY 
DEFERRED
     "$1" FOREIGN KEY (id_ente, id_magazzino, id_settore, id_area) REFERENCES 
area(id_ente, id_magazzino, id_settore, id_area) DEFERRABLE INITIALLY DEFERRED
Rules:
     ubicazione_delete_rule AS ON DELETE TO ubicazione DO INSERT INTO 
ubicazione_trash (id_ente, id_magazzino, id_settore, id_area, id_ubicazione, 
flavor, peso_max, lunghezza, larghezza, altezza, volume_max, inventario, 
allarme, manutenzione, id_produttore, id_articolo, quantita, in_prelievo, 
in_deposito, lotto, scadenza, barcode, tipo, bigoid, metadata, finalized, 
xdbs_created, xdbs_modified) VALUES (old.id_ente, old.id_magazzino, 
old.id_settore, old.id_area, old.id_ubicazione, old.flavor, old.peso_max, 
old.lunghezza, old.larghezza, old.altezza, old.volume_max, old.inventario, 
old.allarme, old.manutenzione, old.id_produttore, old.id_articolo, old.quantita, 
old.in_prelievo, old.in_deposito, old.lotto, old.scadenza, old.barcode, 
old.tipo, old.bigoid, old.metadata, old.finalized, old.xdbs_created, 
old.xdbs_modified)
     ubicazione_update_rule AS ON UPDATE TO ubicazione WHERE 
((new.xdbs_modified)::timestamp with time zone <> now()) DO INSERT INTO 
ubicazione_trash (id_ente, id_magazzino, id_settore, id_area, id_ubicazione, 
flavor, peso_max, lunghezza, larghezza, altezza, volume_max, inventario, 
allarme, manutenzione, id_produttore, id_articolo, quantita, in_prelievo, 
in_deposito, lotto, scadenza, barcode, tipo, bigoid, metadata, finalized, 
xdbs_created, xdbs_modified) VALUES (old.id_ente, old.id_magazzino, 
old.id_settore, old.id_area, old.id_ubicazione, old.flavor, old.peso_max, 
old.lunghezza, old.larghezza, old.altezza, old.volume_max, old.inventario, 
old.allarme, old.manutenzione, old.id_produttore, old.id_articolo, old.quantita, 
old.in_prelievo, old.in_deposito, old.lotto, old.scadenza, old.barcode, 
old.tipo, old.bigoid, old.metadata, old.finalized, old.xdbs_created, 
old.xdbs_modified)
Triggers:
     ubicazione_update_trigger BEFORE UPDATE ON ubicazione FOR EACH ROW EXECUTE 
PROCEDURE xdbs_update_trigger()
Inherits: object,
           barcode

******************************************************************************

Here is the first join. This is planned correctly. Execution times are irrelevant.

dmd-freerp-1-alex=# explain analyze SELECT *  FROM articolo JOIN ubicazione 
USING  (id_ente, id_produttore, id_articolo) WHERE ubicazione.id_ente =  'dmd' 
AND allarme IS NULL AND manutenzione IS NULL AND ubicazione.xdbs_modified > 
'2006-01-08 18:25:00+01';
                                                                           QUERY 
PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
  Nested Loop  (cost=0.00..8.73 rows=1 width=1146) (actual time=0.247..0.247 
rows=0 loops=1)
    ->  Index Scan using ubicazione_modified_index on ubicazione 
(cost=0.00..3.03 rows=1 width=536) (actual time=0.239..0.239 rows=0 loops=1)
          Index Cond: (xdbs_modified > '2006-01-08 18:25:00'::timestamp without 
time zone)
          Filter: ((id_ente = 'dmd'::text) AND (allarme IS NULL) AND 
(manutenzione IS NULL))
    ->  Index Scan using articolo_pkey on articolo  (cost=0.00..5.69 rows=1 
width=653) (never executed)
          Index Cond: (('dmd'::text = articolo.id_ente) AND 
(articolo.id_produttore = "outer".id_produttore) AND (articolo.id_articolo = 
"outer".id_articolo))
  Total runtime: 0.556 ms
(7 rows)

*********************************************************************

Here's the second join on the same tables. This times a different set of indexes 
should be used to perform the join, but even in this case I would expect the 
planner to generate a nested loop of two index scans. Instead, this is what happens.


dmd-freerp-1-alex=# explain analyze SELECT *  FROM articolo JOIN ubicazione 
USING  (id_ente, id_produttore, id_articolo) WHERE ubicazione.id_ente =  'dmd' 
AND allarme IS NULL AND manutenzione IS NULL AND articolo.xdbs_modified > 
'2006-01-08 18:25:00+01';
                                                                           QUERY 
PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
  Nested Loop  (cost=0.00..1017.15 rows=1 width=1146) (actual 
time=258.648..258.648 rows=0 loops=1)
    ->  Seq Scan on ubicazione  (cost=0.00..1011.45 rows=1 width=536) (actual 
time=0.065..51.617 rows=12036 loops=1)
          Filter: ((id_ente = 'dmd'::text) AND (allarme IS NULL) AND 
(manutenzione IS NULL))
    ->  Index Scan using articolo_pkey on articolo  (cost=0.00..5.69 rows=1 
width=653) (actual time=0.011..0.011 rows=0 loops=12036)
          Index Cond: (('dmd'::text = articolo.id_ente) AND 
(articolo.id_produttore = "outer".id_produttore) AND (articolo.id_articolo = 
"outer".id_articolo))
          Filter: (xdbs_modified > '2006-01-08 18:25:00'::timestamp without time 
zone)
  Total runtime: 258.975 ms
(7 rows)

This time, a sequential scan on the rightmost table is used to perform the join. 
This is quite plainly a wrong choice, since the number of tuples in the articolo 
having xdbs_modified > '2006-01-08 18:25:00' is 0. I also tried increasing the 
amount of collected statistics to 1000 with "ALTER TABLE articolo ALTER COLUMN 
xdbs_modified SET STATISTICS 1000" and subsequently vacuum-analyzed the db, so 
as to give the planner as much information as possible to realize that articolo 
ought to be index-scanned with the articolo_modified_index B-tree index. The 
correct query plan is to perform a nested loop join with an index scan on 
articolo using xdbs_modified_index and a corresponding index scan on ubicazione 
using ubicazione_fkey_articolo.

I am currently resorting to selecting from the single tables and performing the 
join in the application code rather than in the DB. This is currently the only 
viable alternative for me, as a 500x speed-down simply cannot be tolerated.

What I do not understand is why the planner behaves so differently in the two 
cases. Any ideas? Would upgrading to more recent versions of postgresql make any 
difference?



Alex



-- 
*********************************************************************
http://www.barettadeit.com/
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tel. +39 02 370 111 55
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Our technology:

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From pgsql-performance-owner@postgresql.org  Mon Jan  9 10:37:04 2006
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Date: Mon, 9 Jan 2006 08:37:04 -0600
From: Kelly Burkhart <kelly.burkhart@gmail.com>
To: Ron <rjpeace@earthlink.net>
Subject: Re: help tuning queries on large database
Cc: pgsql-performance@postgresql.org
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	<7.0.1.0.2.20060108160633.026bd358@earthlink.net>
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On 1/8/06, Ron <rjpeace@earthlink.net> wrote:
>
> <snip>
> Among the other tricks having lots of RAM allows:
> If some of your tables are Read Only or VERY rarely written to, you
> can preload them at boot time and make them RAM resident using the
> /etc/tmpfs trick.


What is the /etc/tmpfs trick?

-K

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On 1/8/06, <b class=3D"gmail_sendername">Ron</b> &lt;<a href=3D"mailto:rjpe=
ace@earthlink.net">rjpeace@earthlink.net</a>&gt; wrote:<div><span class=3D"=
gmail_quote"></span><blockquote class=3D"gmail_quote" style=3D"border-left:=
 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex=
;">
&lt;snip&gt;<br>Among the other tricks having lots of RAM allows:<br>If som=
e of your tables are Read Only or VERY rarely written to, you<br>can preloa=
d them at boot time and make them RAM resident using the<br>/etc/tmpfs tric=
k.
</blockquote><div><br>
What is the /etc/tmpfs trick?<br>
<br>
-K <br>
</div><br></div><br>

------=_Part_22338_28722305.1136817424951--

From pgsql-performance-owner@postgresql.org  Mon Jan  9 11:08:43 2006
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Date: Mon, 09 Jan 2006 16:02:18 +0100
From: Matteo Beccati <php@beccati.com>
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To: Alessandro Baretta <a.baretta@barettadeit.com>
CC: pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong query plan?
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Hi Alessandro,

>  Nested Loop  (cost=0.00..1017.15 rows=1 width=1146) (actual 
> time=258.648..258.648 rows=0 loops=1)
>    ->  Seq Scan on ubicazione  (cost=0.00..1011.45 rows=1 width=536) 
> (actual time=0.065..51.617 rows=12036 loops=1)
>          Filter: ((id_ente = 'dmd'::text) AND (allarme IS NULL) AND 
> (manutenzione IS NULL))

The problem seems here. The planner expects one matching row (and that's 
why it chooses a nested loop), but 12036 rows are matching this condition.

Are you sure that you recentrly ANALYZED the table "ubicazione"? If so, 
try to increase statistics for the id_ente column.


P.S.
There is also an italian mailing list, if you are interested :)

Best regards
--
Matteo Beccati
http://phpadsnew.com
http://phppgads.com

From pgsql-performance-owner@postgresql.org  Mon Jan  9 11:30:22 2006
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Date: Mon, 9 Jan 2006 10:30:21 -0500
From: Jaime Casanova <systemguards@gmail.com>
To: Alessandro Baretta <a.baretta@barettadeit.com>
Subject: Re: 500x speed-down: Wrong query plan?
Cc: pgsql-performance@postgresql.org
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On 1/9/06, Alessandro Baretta <a.baretta@barettadeit.com> wrote:
> Hello gentlemen,
>
> Although this is my first post on the list, I am a fairly experienced Pos=
tgreSQL
> programmer. I am writing an ERP application suite using PostgreSQL as the
> preferred DBMS. Let me state that the SQL DDL is automatically generated =
by a
> CASE tool from an ER model. The generated schema contains the appropriate
> primary key and foreign key constraints, as defined by the original ER mo=
del, as
> well as "reverse indexes" on foreign keys, allowing (in theory) rapid bac=
kward
> navigation of foreign keys in joins.
>
> Let me show a sample join of two tables in the database schema. The infor=
mation
> provided is quite extensive. I'm sorry for that, but I think it is better=
 to
> provide the list with all the relevant information.
>
> Package: postgresql-7.4

maybe, because you are in developing state, you can start to think in
upgrading to 8.1

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)

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From: Harry Jackson <harryjackson@gmail.com>
To: pgsql-performance@postgresql.org
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Subject: Re: Stats collector performance improvement
From: Hannu Krosing <hannu@skype.net>
To: Greg Stark <gsstark@mit.edu>
Cc: Simon Riggs <simon@2ndquadrant.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, Qingqing Zhou <zhouqq@cs.toronto.edu>,
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Ühel kenal päeval, P, 2006-01-08 kell 11:49, kirjutas Greg Stark:
> Hannu Krosing <hannu@skype.net> writes:
> 
> > Interestingly I use pg_stat_activity view to watch for stuck backends,
> > "stuck" in the sense that they have not noticed when client want away
> > and are now waitin the TCP timeout to happen. I query for backends which
> > have been in "<IDLE>" state for longer than XX seconds. I guess that at
> > least some kind of indication for this should be available.
> 
> You mean like the tcp_keepalives_idle option?
> 
> http://www.postgresql.org/docs/8.1/interactive/runtime-config-connection.html#GUC-TCP-KEEPALIVES-IDLE
> 

Kind of, only I'd like to be able to set timeouts less than 120 minutes.

from:
http://developer.apple.com/documentation/mac/NetworkingOT/NetworkingWOT-390.html#HEADING390-0

kp_timeout
        Set the requested timeout value, in minutes. Specify a value of
        T_UNSPEC to use the default value. You may specify any positive
        value for this field of 120 minutes or greater. The timeout
        value is not an absolute requirement; if you specify a value
        less than 120 minutes, TCP will renegotiate a timeout of 120
        minutes.
        
-----------
Hannu



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Subject: Re: Avoiding cartesian product
References: <002b01c610e5$21cc7340$3100000a@demo1>
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Dear Virag,

AFAIK aggregates aren't indexed in postgres (at least not before 8.1, which 
indexes min and max, iirc).

Also, I don't think you need to exactly determine the trace_id. Try this one 
(OTOH; might be wrong):

select DISTINCT ON (a.trace_id, a.seq_no)	-- See below
   b.gc_minor - a.gc_minor, b.gc_major - a.gc_major
from jam_trace_sys a, jam_trace_sys b
where a.trace_id = 22
   and b.trace_id = a.trace_id
   and b.seq_no > a.seq_no			-- Simply ">" is enough
order by a.trace_id, a.seq_no, b.seq_no;	-- DISTINCT, see below

The trick is that DISTINCT takes the first one in each group (IIRC it is 
granted, at least someone told me on one of these lists :) ) so if you order 
by the DISTINCT attributes and then by b.seq_no, you'll get the smallest of 
appropriate b.seq_no values for each DISTINCT values.

The idea of DISTINCTing by both columns is to make sure the planner finds 
the index. (lately I had a similar problem: WHERE a=1 ORDER BY b LIMIT 1 
used an index on b, instead of an (a,b) index. Using ORDER BY a,b solved it)

HTH,

--
G.


On 2006.01.04. 5:12, Virag Saksena wrote:
> 
> I have a table which stores cumulative values
> I would like to display/chart the deltas between successive data 
> collections
>  
> If my primary key only increments by 1, I could write a simple query
>  
> select b.gc_minor - a.gc_minor, b.gc_major - a.gc_major
>   from jam_trace_sys a, jam_trace_sys b
>  where a.trace_id = 22
>    and b.trace_id = a.trace_id
>    and b.seq_no = a.seq_no + 1
>  order by a.seq_no;
>  
> However the difference in sequence number is variable.
> So (in Oracle) I used to extract the next seq_no using a correlated 
> sub-query
>  
> select b.gc_minor - a.gc_minor, b.gc_major - a.gc_major
> from jam_trace_sys a, jam_trace_sys b
> where a.trace_id = 22
> and (b.trace_id, b.seq_no) =
> (select a.trace_id, min(c.seq_no) from jam_trace_sys c
> where c.trace_id = a.trace_id and c.seq_no > a.seq_no)
>  order by a.seq_no;
>  
> For every row in A, The correlated sub-query from C will execute
> With an appropriate index, it will just descend the index Btree
> go one row to the right and return that row (min > :value)
> and join to table B
>  
> SELECT STATEMENT
>   SORT ORDER BY
>    TABLE ACCESS BY INDEX ROWID JAM_TRACE_SYS B
>      NESTED LOOPS
>        TABLE ACCESS BY INDEX ROWID JAM_TRACE_SYS  A
>          INDEX RANGE SCAN JAM_TRACE_SYS_N1  A
>        INDEX RANGE SCAN JAM_TRACE_SYS_N1 B
>          SORT AGGREGATE
>            INDEX RANGE SCAN JAM_TRACE_SYS_N1 C
>  
> In postgreSQL A and B are doing a cartesian product
> then C gets executed for every row in this cartesian product
> and most of the extra rows get thrown out.
> Is there any way to force an execution plan like above where the 
> correlated subquery runs before going to B.
> The table is small right now, but it will grow to have millions of rows
> QUERY PLAN
> -----------------------------------------------------------------------------------------------------------------------------------
>  Sort  (cost=124911.81..124944.84 rows=13213 width=20) (actual 
> time=13096.754..13097.053 rows=149 loops=1)
>    Sort Key: a.seq_no
>    ->  Nested Loop  (cost=4.34..124007.40 rows=13213 width=20) (actual 
> time=1948.300..13096.329 rows=149 loops=1)
>          Join Filter: (subplan)
>          ->  Seq Scan on jam_trace_sys b  (cost=0.00..3.75 rows=175 
> width=16) (actual time=0.005..0.534 rows=175 loops=1)
>          ->  Materialize  (cost=4.34..5.85 rows=151 width=16) (actual 
> time=0.002..0.324 rows=150 loops=175)
>                ->  Seq Scan on jam_trace_sys a  (cost=0.00..4.19 
> rows=151 width=16) (actual time=0.022..0.687 rows=150 loops=1)
>                      Filter: (trace_id = 22)
>          SubPlan
>            ->  Aggregate  (cost=4.67..4.67 rows=1 width=4) (actual 
> time=0.486..0.488 rows=1 loops=26250)
>                  ->  Seq Scan on jam_trace_sys c  (cost=0.00..4.62 
> rows=15 width=4) (actual time=0.058..0.311 rows=74 loops=26250)
>                        Filter: ((trace_id = $0) AND (seq_no > $1))
>  Total runtime: 13097.557 ms
> (13 rows)
>  
> pglnx01=> \d jam_trace_sys
>      Table "public.jam_trace_sys"
>      Column      |  Type   | Modifiers
> -----------------+---------+-----------
>  trace_id        | integer |
>  seq_no          | integer |
>  cpu_utilization | integer |
>  gc_minor        | integer |
>  gc_major        | integer |
>  heap_used       | integer |
> Indexes:
>     "jam_trace_sys_n1" btree (trace_id, seq_no)
>  
> pglnx01=> select count(*) from jam_trace_Sys ;
>  count
> -------
>    175
> (1 row)
>  
> pglnx01=> select trace_id, count(*) from jam_trace_sys group by trace_id ;
>  trace_id | count
> ----------+-------
>        15 |     2
>        18 |    21
>        22 |   150
>        16 |     2
> (4 rows)

From pgsql-performance-owner@postgresql.org  Mon Jan  9 12:23:01 2006
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Date: Mon, 09 Jan 2006 17:23:06 +0100
From: Alessandro Baretta <a.baretta@barettadeit.com>
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To: Matteo Beccati <php@beccati.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong query plan?
References: <43C26A5F.7040702@barettadeit.com> <43C27AFA.7060604@beccati.com>
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Matteo Beccati wrote:
> Hi Alessandro,
> 
>>  Nested Loop  (cost=0.00..1017.15 rows=1 width=1146) (actual 
>> time=258.648..258.648 rows=0 loops=1)
>>    ->  Seq Scan on ubicazione  (cost=0.00..1011.45 rows=1 width=536) 
>> (actual time=0.065..51.617 rows=12036 loops=1)
>>          Filter: ((id_ente = 'dmd'::text) AND (allarme IS NULL) AND 
>> (manutenzione IS NULL))
> 
> 
> The problem seems here. The planner expects one matching row (and that's 
> why it chooses a nested loop), but 12036 rows are matching this condition.
> 
> Are you sure that you recentrly ANALYZED the table "ubicazione"? If so, 
> try to increase statistics for the id_ente column.

No, this is not the problem. I increased the amount of statistics with ALTER 
TABLE ... SET STATISTICS 1000, which is as much as I can have. The problem is 
that the planner simply ignores the right query plan, which is orders of 
magnitude less costly. Keep in mind that the XDBS--the CASE tool I use--makes 
heavy use of indexes, and generates all relevant indexes in relation to the join 
paths which are implicit in the ER model "relations". In this case, both 
ubicazione and articolo have indexes on the join fields:

Indexes:
"articolo_pkey" primary key, btree (id_ente, id_produttore, id_articolo)
"ubicazione_fkey_articolo" btree (id_ente, id_produttore, id_articolo)

Notice that only the "articolo_pkey" is a unique index, while 
"ubicazione_fkey_articolo" allows duplicates. This second index is not used by 
the planner.

Both tables also have a "bookkeeping" index on xdbs_modified. I am selecting 
"recently inserted or updated" tuples, which are usually a very small fraction 
of the table--if there are any. The index on xdbs_modified is B-tree allowing a 
very quick index scan to find the few tuples having xdbs_modified > '[some 
recent timestamp]'. Hence, the optimal plan for both queries is to perform an 
index scan using the <table_name>_modified_index on the table upon which I 
specify the xdbs_modified > '...' condition, and the join-fields index on the 
other table.

Alex

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From pgsql-performance-owner@postgresql.org  Sat Jan 14 01:50:16 2006
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From: "Bernard Dhooghe" <dhoogheb@yahoo.com>
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Subject: >= forces row compare and not index elements compare when possible
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Suppose a table with structure:

Table "public.t4"

 Column |     Type      | Modifiers
--------+---------------+-----------
 c1     | character(10) | not null
 c2     | character(6)  | not null
 c3     | date          | not null
 c4     | character(30) |
 c5     | numeric(10,2) | not null
Indexes:
    "t4_prim" PRIMARY KEY, btree (c1, c2, c3)

Then 2 queries

echo "explain  select * from t4 where (c1,c2,c3) >=
('A','B','1990-01-01') order by c1,c2,c3"|psql test
                                    QUERY PLAN

----------------------------------------------------------------------------------
 Index Scan using t4_prim on t4  (cost=0.00..54.69 rows=740 width=75)
   Filter: (ROW(c1, c2, c3) >= ROW('A'::bpchar, 'B'::bpchar,
'1990-01-01'::date))
(2 rows)

and

echo "explain  select * from t4 where (c1,c2,c3) >=
('A','B','1990-01-01') orde>
                                    QUERY PLAN

----------------------------------------------------------------------------------
 Index Scan using t4_prim on t4  (cost=0.00..54.69 rows=740 width=75)
   Filter: (ROW(c1, c2, c3) >= ROW('A'::bpchar, 'B'::bpchar,
'1990-01-01'::date))
(2 rows)

So switching from (c1,c2,c3) compare from =  to >= makes the optimizer
see the where clause as a row filter, which is not really the case.

Further

echo "explain  select * from t4 where (c1,c2) = ('A','B') order by
c1,c2,c3"|ps>
                            QUERY PLAN
-------------------------------------------------------------------
 Index Scan using t4_prim on t4  (cost=0.00..4.83 rows=1 width=75)
   Index Cond: ((c1 = 'A'::bpchar) AND (c2 = 'B'::bpchar))
(2 rows)

here again the  index can be used (again), the row count can be greater
than one.

but

 echo "explain  select * from t4 where (c1,c2) >= ('A','B') order by
c1,c2,c3"|p>
                              QUERY PLAN
----------------------------------------------------------------------
 Index Scan using t4_prim on t4  (cost=0.00..52.84 rows=740 width=75)
   Filter: (ROW(c1, c2) >= ROW('A'::bpchar, 'B'::bpchar))
(2 rows)


So >= (or <=) is not optimized against an index where it could be.



Bernard Dhooghe


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From: peter royal <peter.royal@pobox.com>
Subject: Re: help tuning queries on large database
Date: Mon, 9 Jan 2006 12:23:15 -0500
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On Jan 8, 2006, at 1:42 PM, Luke Lonergan wrote:
> Have you tested the underlying filesystem for it's performance?   
> Run this:
>   time bash -c 'dd if=/dev/zero of=/my_file_system/bigfile bs=8k
> count=<your_memory_size_in_GB * 250000> && sync'

This is a 2-disk RAID0

[root@bigboy /opt/alt-2]# time bash -c 'dd if=/dev/zero of=/opt/alt-2/ 
bigfile bs=8k count=1000000 && sync'
1000000+0 records in
1000000+0 records out

real    1m27.143s
user    0m0.276s
sys     0m37.338s

'iostat -x' showed writes peaking at ~100MB/s


> Then run this:
>   time dd if=/my_file_system/bigfile bs=8k of=/dev/null

[root@bigboy /opt/alt-2]# time dd if=/opt/alt-2/bigfile bs=8k of=/dev/ 
null
1000000+0 records in
1000000+0 records out

real    1m9.846s
user    0m0.189s
sys     0m11.099s

'iostat -x' showed reads peaking at ~116MB/s


Again with kernel 2.6.15:

[root@bigboy ~]# time bash -c 'dd if=/dev/zero of=/opt/alt-2/bigfile  
bs=8k count=1000000 && sync'
1000000+0 records in
1000000+0 records out

real    1m29.144s
user    0m0.204s
sys     0m48.415s

[root@bigboy ~]# time dd if=/opt/alt-2/bigfile bs=8k of=/dev/null
1000000+0 records in
1000000+0 records out

real    1m9.701s
user    0m0.168s
sys     0m11.933s


> And report the times here please.  With your 8 disks in any of the  
> RAID0
> configurations you describe, you should be getting 480MB/s.  In the  
> RAID10
> configuration you should get 240.

Not anywhere near that. I'm scouring the 'net looking to see what  
needs to be tuned at the HW level.

> You should also experiment with using larger readahead, which you can
> implement like this:
>   blockdev --setra 16384 /dev/<my_block_device>
>
> E.g. "blockdev --setra 16384 /dev/sda"

wow, this helped nicely. Without using the updated kernel, it took  
28% off my testcase time.

> From what you describe, one of these is likely:
> - hardware isn't configured properly or a driver problem.

Using the latest Areca driver, looking to see if there is some  
configuration that was missed.

> - you need to use xfs and tune your Linux readahead

Will try XFS soon, concentrating on the 'dd' speed issue first.


On Jan 8, 2006, at 4:35 PM, Ron wrote:
>> Areca ARC-1220 8-port PCI-E controller
>
> Make sure you have 1GB or 2GB of cache.  Get the battery backup and  
> set the cache for write back rather than write through.

The card we've got doesn't have a SODIMM socket, since its only an 8- 
port card.  My understanding was that was cache used when writing?

> A 2.6.12 or later based Linux distro should have NO problems using  
> more than 4GB or RAM.

Upgraded the kernel to 2.6.15, then we were able to set the BIOS  
option for the 'Memory Hole' to 'Software' and it saw all 4G (under  
2.6.11 we got a kernel panic with that set)

>> RAID Layout:
>>
>> 4 2-disk RAID0 sets created
> You do know that a RAID 0 set provides _worse_ data protection than  
> a single HD?  Don't use RAID 0 for any data you want kept reliably.

yup, aware of that. was planning on RAID10 for production, but just  
broke it out into RAID0 sets for testing (from what I read, I  
gathered that the read performance of RAID0 and RAID10 were comparable)


thanks for all the suggestions, I'll report back as I continue testing.

-pete

-- 
(peter.royal|osi)@pobox.com - http://fotap.org/~osi


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From pgsql-performance-owner@postgresql.org  Mon Jan  9 14:41:22 2006
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To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: Matteo Beccati <php@beccati.com>, pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong query plan? 
In-reply-to: <43C28DEA.60801@barettadeit.com> 
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	<43C28DEA.60801@barettadeit.com>
Comments: In-reply-to Alessandro Baretta <a.baretta@barettadeit.com>
	message dated "Mon, 09 Jan 2006 17:23:06 +0100"
Date: Mon, 09 Jan 2006 13:41:05 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
> Matteo Beccati wrote:
>> Are you sure that you recentrly ANALYZED the table "ubicazione"? If so, 
>> try to increase statistics for the id_ente column.

> No, this is not the problem. I increased the amount of statistics with ALTER 
> TABLE ... SET STATISTICS 1000, which is as much as I can have.

What Matteo wanted to know is if you'd done an ANALYZE afterward.  ALTER
TABLE SET STATISTICS doesn't in itself update the statistics.

What do you get from

EXPLAIN SELECT * FROM articolo WHERE articolo.xdbs_modified > '2006-01-08 18:25:00+01';

I'm curious to see how many rows the planner thinks this will produce,
and whether it will use the index or not.

Also, I gather from the plan choices that the condition id_ente = 'dmd'
isn't very selective ... what fraction of the rows in each table
satisfy that?

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan  9 14:50:15 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>,
	pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong query plan?
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	<43C28DEA.60801@barettadeit.com> <6719.1136832065@sss.pgh.pa.us>
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Tom Lane wrote:
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
> 
>>Matteo Beccati wrote:
>>
>>>Are you sure that you recentrly ANALYZED the table "ubicazione"? If so, 
>>>try to increase statistics for the id_ente column.
> 
> 
>>No, this is not the problem. I increased the amount of statistics with ALTER 
>>TABLE ... SET STATISTICS 1000, which is as much as I can have.
> 
> 
> What Matteo wanted to know is if you'd done an ANALYZE afterward.  ALTER
> TABLE SET STATISTICS doesn't in itself update the statistics.

I probably forgot to mention that I have vacuum-analyze the after this 
operation, and, since I did not manage to get the index to work, I 
vacuum-analyzed several times more, just to be on the safe side.

> What do you get from
> 
> EXPLAIN SELECT * FROM articolo WHERE articolo.xdbs_modified > '2006-01-08 18:25:00+01';
> 
> I'm curious to see how many rows the planner thinks this will produce,
> and whether it will use the index or not.

dmd-freerp-1-alex=# EXPLAIN ANALYZE SELECT * FROM articolo WHERE 
articolo.xdbs_modified > '2006-01-08 18:25:00+01';
                                                                 QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
  Index Scan using articolo_modified_index on articolo  (cost=0.00..3914.91 
rows=17697 width=653) (actual time=0.032..0.032 rows=0 loops=1)
    Index Cond: (xdbs_modified > '2006-01-08 18:25:00'::timestamp without time zone)
  Total runtime: 0.150 ms
(3 rows)

The planner gets tricked only by *SOME* join queries.


> Also, I gather from the plan choices that the condition id_ente = 'dmd'
> isn't very selective ... what fraction of the rows in each table
> satisfy that?

In most situation, this condition selects all the tuples. "id_ente" selects the 
"owner of the data". Since, in most situations, companies do not share a 
database between them--although the application allows it--filtering according 
to 'id_ente' is like to filtering at all. Yet, this field is used in the 
indexes, so the condition ought to be specified in the queries anyhow.

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Question,

How exactly is Postgres and Linux use the memory?

I have serveral databases that have multi GB indexes on very large tables.
On our current servers, the indexes can fit into memory but not the data
(servers have 8 - 12 GB).  However, my boss is wanting to get new servers
for me but does not want to keep the memory requirements as high as they ar=
e
now (this will allow us to get more servers to spread our 200+ databases
over).

Question, if I have a 4GB+ index for a table on a server with 4GB ram, and =
I
submit a query that does an index scan, does Postgres read the entire index=
,
or just read the index until it finds the matching value (our extra large
indexes are primary keys).

I am looking for real number to give to my boss the say either having a
primary key larger than our memory is bad (and how to clearly justfify it),
or it is ok.

If it is ok, what are the trade offs in performance?\

Obviously, I want more memory, but I have to prove the need to my boss sinc=
e
it raises the cost of the servers a fair amount.

Thanks for any help,

Chris

------=_Part_84319_23632822.1136832888923
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

Question,<br>
<br>
How exactly is Postgres and Linux use the memory?<br>
<br>
I have serveral databases that have multi GB indexes on very large
tables.&nbsp; On our current servers, the indexes can fit into memory
but not the data (servers have 8 - 12 GB).&nbsp; However, my boss is
wanting to get new servers for me but does not want to keep the memory
requirements as high as they are now (this will allow us to get more
servers to spread our 200+ databases over).<br>
<br>
Question, if I have a 4GB+ index for a table on a server with 4GB ram,
and I submit a query that does an index scan, does Postgres read the
entire index, or just read the index until it finds the matching value
(our extra large indexes are primary keys).<br>
<br>
I am looking for real number to give to my boss the say either having a
primary key larger than our memory is bad (and how to clearly justfify
it), or it is ok.<br>
<br>
If it is ok, what are the trade offs in performance?\<br>
<br>
Obviously, I want more memory, but I have to prove the need to my boss sinc=
e it raises the cost of the servers a fair amount.<br>
<br>
Thanks for any help,<br>
<br>
Chris<br>

------=_Part_84319_23632822.1136832888923--

From pgsql-performance-owner@postgresql.org  Mon Jan  9 14:56:55 2006
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To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: Matteo Beccati <php@beccati.com>, pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong query plan? 
In-reply-to: <43C2B06B.4050506@barettadeit.com> 
References: <43C26A5F.7040702@barettadeit.com> <43C27AFA.7060604@beccati.com>
	<43C28DEA.60801@barettadeit.com> <6719.1136832065@sss.pgh.pa.us>
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Comments: In-reply-to Alessandro Baretta <a.baretta@barettadeit.com>
	message dated "Mon, 09 Jan 2006 19:50:19 +0100"
Date: Mon, 09 Jan 2006 13:56:50 -0500
Message-ID: <6914.1136833010@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
> Tom Lane wrote:
>> I'm curious to see how many rows the planner thinks this will produce,
>> and whether it will use the index or not.

> dmd-freerp-1-alex=# EXPLAIN ANALYZE SELECT * FROM articolo WHERE 
> articolo.xdbs_modified > '2006-01-08 18:25:00+01';
>                                                                  QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------------------
>   Index Scan using articolo_modified_index on articolo  (cost=0.00..3914.91 
> rows=17697 width=653) (actual time=0.032..0.032 rows=0 loops=1)
>     Index Cond: (xdbs_modified > '2006-01-08 18:25:00'::timestamp without time zone)
>   Total runtime: 0.150 ms
> (3 rows)

Well, there's your problem: 17697 rows estimated vs 0 actual.  With a
closer row estimate it would've probably done the right thing for the
join problem.

How many rows are really in the table, anyway?  Could we see the
pg_stats row for articolo.xdbs_modified?

			regards, tom lane

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Date: Mon, 09 Jan 2006 11:01:43 -0800
Subject: Re: help tuning queries on large database
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "peter royal" <peter.royal@pobox.com>,
	pgsql-performance@postgresql.org
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Peter,

On 1/9/06 9:23 AM, "peter royal" <peter.royal@pobox.com> wrote:

> This is a 2-disk RAID0

Your 2-disk results look fine - what about your 8-disk results?

Given that you want to run in production with RAID10, the most you should
expect is 2x the 2-disk results using all 8 of your disks.  If you want the
best rate for production while preserving data integrity, I recommend
running your Areca in RAID5, in which case you should expect 3.5x your
2-disk results (7 drives).  You can assume you'll get that if you use XFS +
readahead.  OTOH - I'd like to see your test results anyway :-)

- Luke



From pgsql-admin-owner@postgresql.org  Mon Jan  9 16:36:02 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Chris Hoover <revoohc@gmail.com>
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On Mon, Jan 09, 2006 at 01:54:48PM -0500, Chris Hoover wrote:
> Question, if I have a 4GB+ index for a table on a server with 4GB ram, and I
> submit a query that does an index scan, does Postgres read the entire index,
> or just read the index until it finds the matching value (our extra large
> indexes are primary keys).

Well, the idea behind an index is that if you need a specific value from
it, you can get there very quickly, reading a minimum of data along the
way. So basically, PostgreSQL won't normally read an entire index.

> I am looking for real number to give to my boss the say either having a
> primary key larger than our memory is bad (and how to clearly justfify it),
> or it is ok.
> 
> If it is ok, what are the trade offs in performance?\
> 
> Obviously, I want more memory, but I have to prove the need to my boss since
> it raises the cost of the servers a fair amount.

Well, if you add a sleep to the following code, you can tie up some
amount of memory, which would allow you to simulate having less memory
available. Though over time I think the kernel might decide to page that
memory out, so it's not perfect.

int main(int argc, char *argv[]) {
    if (!calloc(atoi(argv[1]), 1024*1024)) { printf("Error allocating memory.\n"); }
}

In a nutshell, PostgreSQL and the OS will generally work together to
only cache data that is being used fairly often. In the case of a large
PK index, if you're not actually reading a large distribution of the
values in the index you probably aren't even caching the entire index
even now. There may be some kind of linux tool that would show you what
portion of a file is currently cached, which would help answer that
question (but remember that hopefully whatever parts of the index are
cached by PostgreSQL itself won't also be cached by the OS as well).
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Mon Jan  9 16:59:53 2006
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From: peter royal <peter.royal@pobox.com>
Subject: Re: help tuning queries on large database
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On Jan 9, 2006, at 2:01 PM, Luke Lonergan wrote:
> Peter,
>
> On 1/9/06 9:23 AM, "peter royal" <peter.royal@pobox.com> wrote:
>
>> This is a 2-disk RAID0
>
> Your 2-disk results look fine - what about your 8-disk results?

after some further research the 2-disk RAID0 numbers are not bad.

I have a single drive of the same type hooked up to the SATA2 port on  
the motherboard to boot from, and its performance numbers are (linux  
2.6.15, ext3):

[root@bigboy ~]# time bash -c 'dd if=/dev/zero of=/tmp/bigfile bs=8k  
count=1000000 && sync'
1000000+0 records in
1000000+0 records out

real    4m55.032s
user    0m0.256s
sys     0m47.299s
[root@bigboy ~]# time dd if=/tmp/bigfile bs=8k of=/dev/null
1000000+0 records in
1000000+0 records out

real    3m27.229s
user    0m0.156s
sys     0m13.377s

so, there is a clear advantage to RAID over a single drive.


now, some stats in a 8-disk configuration:

8-disk RAID0, ext3, 16k read-ahead

[root@bigboy /opt/pgdata]# time bash -c 'dd if=/dev/zero of=/opt/ 
pgdata/bigfile bs=8k count=1000000 && sync'
1000000+0 records in
1000000+0 records out

real    0m53.030s
user    0m0.204s
sys     0m42.015s

[root@bigboy /opt/pgdata]# time dd if=/opt/pgdata/bigfile bs=8k of=/ 
dev/null
1000000+0 records in
1000000+0 records out

real    0m23.232s
user    0m0.144s
sys     0m13.213s


8-disk RAID0, xfs, 16k read-ahead

[root@bigboy /opt/pgdata]# time bash -c 'dd if=/dev/zero of=/opt/ 
pgdata/bigfile bs=8k count=1000000 && sync'
1000000+0 records in
1000000+0 records out

real    0m32.177s
user    0m0.212s
sys     0m21.277s

[root@bigboy /opt/pgdata]# time dd if=/opt/pgdata/bigfile bs=8k of=/ 
dev/null
1000000+0 records in
1000000+0 records out

real    0m21.814s
user    0m0.172s
sys     0m13.881s


... WOW.. highly impressed with the XFS write speed! going to stick  
with that!

Overall, I got a 50% boost in the overall speed of my test suite by  
using XFS and the 16k read-ahead.

> Given that you want to run in production with RAID10, the most you  
> should
> expect is 2x the 2-disk results using all 8 of your disks.  If you  
> want the
> best rate for production while preserving data integrity, I recommend
> running your Areca in RAID5, in which case you should expect 3.5x your
> 2-disk results (7 drives).  You can assume you'll get that if you  
> use XFS +
> readahead.  OTOH - I'd like to see your test results anyway :-)

I've been avoiding RAID5 after reading how performance drops when a  
drive is out/rebuilding. The performance benefit will outweigh the  
cost I think.

Thanks for the help!
-pete

-- 
(peter.royal|osi)@pobox.com - http://fotap.org/~osi


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From pgsql-performance-owner@postgresql.org  Mon Jan  9 18:01:12 2006
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Date: Mon, 09 Jan 2006 13:29:30 -0800
Subject: Re: help tuning queries on large database
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "peter royal" <peter.royal@pobox.com>,
	pgsql-performance@postgresql.org
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Peter,

On 1/9/06 12:59 PM, "peter royal" <peter.royal@pobox.com> wrote:


> Overall, I got a 50% boost in the overall speed of my test suite by
> using XFS and the 16k read-ahead.

Yes, it all looks pretty good for your config, though it looks like you
might be adapter limited with the Areca - you should have seen a read time
with XFS of about 17 seconds.

OTOH - with RAID5, you are probably about balanced, you should see a read
time of about 19 seconds and instead you'll get your 22 which isn't too big
of a deal.
 
> Thanks for the help!

Sure - no problem!

BTW - I'm running tests right now with the 3Ware 9550SX controllers.  Two of
them on one machine running simultaneously with 16 drives and we're getting
800MB/s sustained read times.  That's a 32GB file read in 40 seconds (!!)

At that rate, we're only about 3x slower than memory access (practically
limited at around 2GB/s even though the system bus peak is 10GB/s). So, the
point is, if you want to get close to your "warm" speed, you need to get
your disk I/O as close to main memory speed as you can.  With parallel I/O
you can do that (see Bizgres MPP for more).

- Luke



From pgsql-performance-owner@postgresql.org  Mon Jan  9 19:50:43 2006
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Subject: Re: [PERFORMANCE] Beetwen text and varchar field
In-Reply-To: <20060109114940.GB28748@uio.no>
To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
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See the FAQ.

---------------------------------------------------------------------------

Steinar H. Gunderson wrote:
> On Mon, Jan 09, 2006 at 11:58:19AM +0100, TNO wrote:
> > what is the best for a char field with less than 1000 characters?
> > a text field or a varchar(1000)
> 
> They will be equivalent. text and varchar are the same type internally -- the
> only differences are that varchar can have a length (but does not need one),
> and that some casts are only defined for text.
> 
> If there's really a natural thousand-character limit to the data in question,
> use varchar(1000); if not, use text or varchar, whatever you'd like.
> 
> /* Steinar */
> -- 
> Homepage: http://www.sesse.net/
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-performance-owner@postgresql.org  Mon Jan  9 21:44:55 2006
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Date: Tue, 10 Jan 2006 02:44:47 +0100
From: Andrea Arcangeli <andrea@cpushare.com>
To: pgsql-performance@postgresql.org
Subject: NOT LIKE much faster than LIKE?
Message-ID: <20060110014447.GB18474@opteron.random>
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Hello,

I've a performance problem with the planner algorithm choosen in a website.
See the difference between this:

	http://klive.cpushare.com/?scheduler=cooperative

and this:

	http://klive.cpushare.com/?scheduler=preemptive

(note, there's much less data to show with preemptive, so it's not because of
the amount of data to output)

The second takes ages to complete and it overloads the server as well at 100%
cpu load for several seconds.

"cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
"preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference
is a NOT before "LIKE". No other differences at all.

The planner does apparently a big mistake using the nested loop in the "LIKE"
query, it should use the hash join lik in the "NOT LIKE" query instead.

I guess I can force it somehow (I found some docs about it here:

	http://www.postgresql.org/docs/8.1/static/runtime-config-query.html

) but it looks like something could be improved in the default mode too, so I'm
reporting the problem since it looks a performance bug to me. It just makes no
sense to me that the planner takes a difference decision based on a "not". It
can't know if it's more likely or less likely, this is a boolean return, it's
*exactly* the same cost to run it. Making assumption without user-provided
hints looks a mistake. I never said to the db that "not like" is more or less
likely to return data in output than "like".

Tried ANALYZE, including VACUUM FULL ANALYZE and it doesn't make a difference.

Perhaps it's analyze that suggests to use a different algorithm with "not like"
because there's much more data to analyze with "not like" than with "like", but
that algorithm works much better even when there's less data to analyze.

Indexes don't make any visible difference.

postgres is version 8.1.2 self compiled from CVS 8.1 branch of yesterday.

psandrea@opteron:~> psql -V
psql (PostgreSQL) 8.1.2
contains support for command-line editing
andrea@opteron:~> 

The problem is reproducible on the shell, I only need to remove "explain". Of
course explain is wrong about the cost, according to explain the first query is
cheaper when infact it's an order of magnitude more costly.

klive=> explain SELECT class, vendor, device, revision, COUNT(*) as nr FROM pci NATURAL INNER JOIN klive WHERE kernel_version LIKE '%% PREEMPT %%' GROUP BY class, vendor, device, revision;
                                      QUERY PLAN
--------------------------------------------------------------------------------------
 HashAggregate  (cost=1687.82..1687.83 rows=1 width=16)
   ->  Nested Loop  (cost=235.86..1687.81 rows=1 width=16)
         ->  Seq Scan on klive  (cost=0.00..1405.30 rows=1 width=8)
               Filter: ((kernel_version)::text ~~ '%% PREEMPT %%'::text)
         ->  Bitmap Heap Scan on pci  (cost=235.86..282.32 rows=15 width=24)
               Recheck Cond: (pci.klive = "outer".klive)
               ->  Bitmap Index Scan on pci_pkey  (cost=0.00..235.86 rows=15 width=0)
                     Index Cond: (pci.klive = "outer".klive)
(8 rows)

klive=> explain SELECT class, vendor, device, revision, COUNT(*) as nr FROM pci NATURAL INNER JOIN klive WHERE kernel_version NOT LIKE '%% PREEMPT %%' GROUP BY class, vendor, device, revision;
                                   QUERY PLAN
--------------------------------------------------------------------------------
 HashAggregate  (cost=3577.40..3612.00 rows=2768 width=16)
   ->  Hash Join  (cost=1569.96..3231.50 rows=27672 width=16)
         Hash Cond: ("outer".klive = "inner".klive)
         ->  Seq Scan on pci  (cost=0.00..480.73 rows=27673 width=24)
         ->  Hash  (cost=1405.30..1405.30 rows=22263 width=8)
               ->  Seq Scan on klive  (cost=0.00..1405.30 rows=22263 width=8)
                     Filter: ((kernel_version)::text !~~ '%% PREEMPT %%'::text)
(7 rows)

klive=> 

Hints welcome, thanks!


PS. All the source code of the website where I'm reproducing the problem is
available at the above url under the GPL.

From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:04:49 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
In-reply-to: <20060110014447.GB18474@opteron.random> 
References: <20060110014447.GB18474@opteron.random>
Comments: In-reply-to Andrea Arcangeli <andrea@cpushare.com>
	message dated "Tue, 10 Jan 2006 02:44:47 +0100"
Date: Mon, 09 Jan 2006 21:04:48 -0500
Message-ID: <24021.1136858688@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Andrea Arcangeli <andrea@cpushare.com> writes:
> It just makes no sense to me that the planner takes a difference
> decision based on a "not".

Why in the world would you think that?  In general a NOT will change the
selectivity of the WHERE condition tremendously.  If the planner weren't
sensitive to that, *that* would be a bug.  The only case where it's
irrelevant is if the selectivity of the base condition is exactly 50%,
which is not a very reasonable default guess for LIKE.

It sounds to me that the problem is misestimation of the selectivity
of the LIKE pattern --- the planner is going to think that
LIKE '%% PREEMPT %%' is fairly selective because of the rather long
match text, when in reality it's probably not so selective on your
data.  But we don't keep any statistics that would allow the actual
number of matching rows to be estimated well.  You might want to think
about changing your data representation so that the pattern-match can be
replaced by a boolean column, or some such, so that the existing
statistics code can make a more reasonable estimate how many rows are
selected.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:23:07 2006
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From: Andrea Arcangeli <andrea@cpushare.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
Message-ID: <20060110022303.GA20168@opteron.random>
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	<24021.1136858688@sss.pgh.pa.us>
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On Mon, Jan 09, 2006 at 09:04:48PM -0500, Tom Lane wrote:
> Andrea Arcangeli <andrea@cpushare.com> writes:
> > It just makes no sense to me that the planner takes a difference
> > decision based on a "not".
> 
> Why in the world would you think that?  In general a NOT will change the
> selectivity of the WHERE condition tremendously.  If the planner weren't
> sensitive to that, *that* would be a bug.  The only case where it's
> irrelevant is if the selectivity of the base condition is exactly 50%,
> which is not a very reasonable default guess for LIKE.

How do you know that "LIKE" will have a selectivity above 50% in the
first place? I think 50% should be the default unless the selectively is
measured at runtime against the data being queried.

If you don't know the data, I think it's a bug that LIKE is assumed to
have a selectivity above 50%. You can't know that, only the author of
the code can know that and that's why I talked about hints. It'd be fine
to give hints like:

	UNLIKELY string LIKE '%% PREEMPT %%'

or:

	LIKELY string NOT LIKE '%% PREEMPT %%'

Then you could assume that very little data will be returned or a lot of
data will be returned. 

If you don't get hints NOT LIKE or LIKE should be assumed to have the
same selectivity.

> It sounds to me that the problem is misestimation of the selectivity
> of the LIKE pattern --- the planner is going to think that
> LIKE '%% PREEMPT %%' is fairly selective because of the rather long
> match text, when in reality it's probably not so selective on your
> data.  But we don't keep any statistics that would allow the actual

True, there's a lot of data that matches %% PREEMPT %% (even if less
than the NOT case).

> number of matching rows to be estimated well.  You might want to think
> about changing your data representation so that the pattern-match can be
> replaced by a boolean column, or some such, so that the existing
> statistics code can make a more reasonable estimate how many rows are
> selected.

I see. I can certainly fix it by stopping using LIKE. But IMHO this
remains a bug, since until the statistics about the numberof matching
rows isn't estimated well, you should not make assumptions on LIKE/NOT
LIKE. I think you can change the code in a way that I won't have to
touch anything, and this will lead to fewer surprises in the future IMHO.

Thanks!

From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:27:50 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
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Subject: Re: NOT LIKE much faster than LIKE?
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> 	UNLIKELY string LIKE '%% PREEMPT %%'
> 
> or:
> 
> 	LIKELY string NOT LIKE '%% PREEMPT %%'

You should be using contrib/tsearch2 for an un-anchored text search perhaps?


From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:45:34 2006
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Date: Tue, 10 Jan 2006 03:45:34 +0100
From: Andrea Arcangeli <andrea@cpushare.com>
To: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Tue, Jan 10, 2006 at 10:29:05AM +0800, Christopher Kings-Lynne wrote:
> >	UNLIKELY string LIKE '%% PREEMPT %%'
> >
> >or:
> >
> >	LIKELY string NOT LIKE '%% PREEMPT %%'
> 
> You should be using contrib/tsearch2 for an un-anchored text search perhaps?

If I wanted to get the fastest speed possible, then I think parsing it
with python and storing true/false in a boolean like suggested before
would be better and simpler as well for this specific case.

However I don't need big performance, I need just decent performance, and it
annoys me that there heurisics where the LIKE query assumes little data
will be selected. There's no way to know that until proper stats are
recorded on the results of the query. The default should be good enough
to use IMHO, and there's no way to know if NOT LIKE or LIKE will return
more data, 50% should be assumed for both if no runtime information is
available IMHO.

IIRC gcc in a code like if (something) {a}  else {b} assumes that a is
more likely to be executed then b, but that's because it's forced to
choose something. Often one is forced to choose what is more likely
between two events, but I don't think the above falls in this case. I
guess the heuristic really wanted to speed up the runtime of LIKE, when
it actually made it a _lot_ worse. No heuristic is better than an
heuristic that falls apart in corner cases like the above "LIKE".

From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:54:43 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
In-reply-to: <20060110022303.GA20168@opteron.random> 
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Comments: In-reply-to Andrea Arcangeli <andrea@cpushare.com>
	message dated "Tue, 10 Jan 2006 03:23:03 +0100"
Date: Mon, 09 Jan 2006 21:54:44 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Andrea Arcangeli <andrea@cpushare.com> writes:
> If you don't know the data, I think it's a bug that LIKE is assumed to
> have a selectivity above 50%.

Extrapolating from the observation that the heuristics don't work well
on your data to the conclusion that they don't work for anybody is not
good logic.  Replacing that code with a flat 50% is not going to happen
(or if it does, I'll be sure to send the mob of unhappy users waving
torches and pitchforks to your door not mine ;-)).

I did just think of something we could improve though.  The pattern
selectivity code doesn't make any use of the statistics about "most
common values".  For a constant pattern, we could actually apply the
pattern test with each common value and derive answers that are exact
for the portion of the population represented by the most-common-values
list.  If the MCV list covers a large fraction of the population then
this would be a big leg up in accuracy.  Dunno if that applies to your
particular case or not, but it seems worth doing ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan  9 22:54:57 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Tue, 10 Jan 2006, Andrea Arcangeli wrote:

> I see. I can certainly fix it by stopping using LIKE. But IMHO this
> remains a bug, since until the statistics about the numberof matching
> rows isn't estimated well, you should not make assumptions on LIKE/NOT
> LIKE. I think you can change the code in a way that I won't have to
> touch anything, and this will lead to fewer surprises in the future IMHO.

I doubt it, since I would expect that this would be as large a
pessimization for a larger fraction of people than it is an optimization
for you.

From pgsql-performance-owner@postgresql.org  Mon Jan  9 23:47:22 2006
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Subject: Re: NOT LIKE much faster than LIKE?
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On Mon, Jan 09, 2006 at 09:54:44PM -0500, Tom Lane wrote:
> Extrapolating from the observation that the heuristics don't work well
> on your data to the conclusion that they don't work for anybody is not
> good logic.  Replacing that code with a flat 50% is not going to happen
> (or if it does, I'll be sure to send the mob of unhappy users waving
> torches and pitchforks to your door not mine ;-)).

I'm not convinced but of course I cannot exclude that some people may be
depending on this very heuristic. But I consider this being
bug-compatible, I've an hard time to be convinced that such heuristic
isn't going to bite other people like it did with me.

> I did just think of something we could improve though.  The pattern
> selectivity code doesn't make any use of the statistics about "most
> common values".  For a constant pattern, we could actually apply the
> pattern test with each common value and derive answers that are exact
> for the portion of the population represented by the most-common-values
> list.  If the MCV list covers a large fraction of the population then
> this would be a big leg up in accuracy.  Dunno if that applies to your
> particular case or not, but it seems worth doing ...

Fixing this with proper stats would be great indeed. What would be the
most common value for the kernel_version? You can see samples of the
kernel_version here http://klive.cpushare.com/2.6.15/ .  That's the
string that is being searched against both PREEMPT and SMP.

BTW, I also run a LIKE '%% SMP %%' a NOT LIKE '%% SMP %%' but that runs
fine, probably because as you said in the first email PREEMPT is long
but SMP is short.

Thanks!

From pgsql-performance-owner@postgresql.org  Tue Jan 10 00:30:35 2006
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Date: Mon, 9 Jan 2006 21:23:38 -0700
From: Robert Creager <Robert_Creager@LogicalChaos.org>
To: PGPerformance <pgsql-performance@postgresql.org>
Subject: Index isn't used during a join.
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Hey folks,

I'm working with a query to get more info out with a join.  The base query =
works great speed wise because of index usage.  When the join is tossed in,=
 the index is no longer used, so the query performance tanks.

Can anyone advise on how to get the index usage back?

weather=3D# select version();
                                                        version            =
                                           =20
---------------------------------------------------------------------------=
--------------------------------------------
 PostgreSQL 8.1.1 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 4.0.1 (4.=
0.1-5mdk for Mandriva Linux release 2006.0)
(1 row)

The base query is:

weather=3D# EXPLAIN ANALYZE
weather-# SELECT min_reading, max_reading, avg_reading, -- doy,
weather-#        unmunge_time( time_group ) AS time
weather-# FROM minute."windspeed"
weather-# --JOIN readings_doy ON EXTRACT( doy FROM unmunge_time( time_group=
 ) ) =3D doy
weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interval )
weather-# ORDER BY time_group;
                                                                 QUERY PLAN=
                                                                 =20
---------------------------------------------------------------------------=
------------------------------------------------------------------
 Sort  (cost=3D10995.29..11155.58 rows=3D64117 width=3D28) (actual time=3D4=
.509..4.574 rows=3D285 loops=3D1)
   Sort Key: time_group
   ->  Bitmap Heap Scan on windspeed  (cost=3D402.42..5876.05 rows=3D64117 =
width=3D28) (actual time=3D0.784..3.639 rows=3D285 loops=3D1)
         Recheck Cond: (unmunge_time(time_group) > (now() - '24:00:00'::int=
erval))
         ->  Bitmap Index Scan on minute_windspeed_index  (cost=3D0.00..402=
.42 rows=3D64117 width=3D0) (actual time=3D0.675..0.675 rows=3D285 loops=3D=
1)
               Index Cond: (unmunge_time(time_group) > (now() - '24:00:00':=
:interval))
 Total runtime: 4.880 ms
(7 rows)

When I add in the join, the query tosses out the nice quick index in favor =
of sequence scans:

weather=3D# EXPLAIN ANALYZE
weather-# SELECT min_reading, max_reading, avg_reading, -- doy,
weather-#        unmunge_time( time_group ) AS time
weather-# FROM minute."windspeed"
weather-# JOIN readings_doy ON EXTRACT( doy FROM unmunge_time( time_group )=
 ) =3D doy
weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interval )
weather-# ORDER BY time_group;
                                                               QUERY PLAN  =
                                                             =20
---------------------------------------------------------------------------=
--------------------------------------------------------------
 Sort  (cost=3D98239590.88..99052623.66 rows=3D325213113 width=3D28) (actua=
l time=3D60136.484..61079.845 rows=3D1030656 loops=3D1)
   Sort Key: windspeed.time_group
   ->  Merge Join  (cost=3D265774.21..8396903.54 rows=3D325213113 width=3D2=
8) (actual time=3D34318.334..47113.277 rows=3D1030656 loops=3D1)
         Merge Cond: ("outer"."?column5?" =3D "inner"."?column2?")
         ->  Sort  (cost=3D12997.68..13157.98 rows=3D64120 width=3D28) (act=
ual time=3D2286.155..2286.450 rows=3D284 loops=3D1)
               Sort Key: date_part('doy'::text, unmunge_time(windspeed.time=
_group))
               ->  Seq Scan on windspeed  (cost=3D0.00..7878.18 rows=3D6412=
0 width=3D28) (actual time=3D2279.275..2285.271 rows=3D284 loops=3D1)
                     Filter: (unmunge_time(time_group) > (now() - '24:00:00=
'::interval))
         ->  Sort  (cost=3D252776.54..255312.51 rows=3D1014389 width=3D8) (=
actual time=3D32001.370..33473.407 rows=3D1051395 loops=3D1)
               Sort Key: date_part('doy'::text, readings."when")
               ->  Seq Scan on readings  (cost=3D0.00..142650.89 rows=3D101=
4389 width=3D8) (actual time=3D0.053..13759.015 rows=3D1014448 loops=3D1)
 Total runtime: 61720.935 ms
(12 rows)

weather=3D# \d minute.windspeed
          Table "minute.windspeed"
   Column    |       Type       | Modifiers=20
-------------+------------------+-----------
 time_group  | integer          | not null
 min_reading | double precision | not null
 max_reading | double precision | not null
 avg_reading | double precision | not null
Indexes:
    "windspeed_pkey" PRIMARY KEY, btree (time_group)
    "minute_windspeed_index" btree (unmunge_time(time_group))

CREATE OR REPLACE FUNCTION unmunge_time( integer )
RETURNS timestamp AS '
DECLARE
   input ALIAS FOR $1;
BEGIN
   RETURN (''epoch''::timestamptz + input * ''1sec''::interval)::timestamp;
END;
' LANGUAGE plpgsql IMMUTABLE STRICT;

weather=3D# \d readings
                                             Table "public.readings"
        Column        |            Type             |                      =
    Modifiers                         =20
----------------------+-----------------------------+----------------------=
---------------------------------------
 when                 | timestamp without time zone | not null default (tim=
eofday())::timestamp without time zone
 hour_group           | integer                     |=20
 minute_group         | integer                     |=20
 day_group            | integer                     |=20
 week_group           | integer                     |=20
 month_group          | integer                     |=20
 year_group           | integer                     |=20
 year_group_updated   | boolean                     | default false
 month_group_updated  | boolean                     | default false
 week_group_updated   | boolean                     | default false
 day_group_updated    | boolean                     | default false
 hour_group_updated   | boolean                     | default false
 minute_group_updated | boolean                     | default false
Indexes:
    "readings_pkey" PRIMARY KEY, btree ("when")
    "day_group_updated_index" btree (day_group_updated, day_group)
    "hour_group_updated_index" btree (hour_group_updated, hour_group)
    "month_group_updated_index" btree (month_group_updated, month_group)
    "readings_doy_index" btree (date_part('doy'::text, "when"))
    "week_group_updated_index" btree (week_group_updated, week_group)
    "year_group_updated_index" btree (year_group_updated, year_group)
Triggers:
    munge_time BEFORE INSERT OR UPDATE ON readings FOR EACH ROW EXECUTE PRO=
CEDURE munge_time()

readings_doy is a view that adds date_part('doy'::text, readings."when") AS=
 doy to the readings table.

Thanks,
Rob

--=20
 21:15:51 up 2 days, 13:42,  9 users,  load average: 3.14, 2.63, 2.62
Linux 2.6.12-12-2 #4 SMP Tue Jan 3 19:56:19 MST 2006

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From pgsql-performance-owner@postgresql.org  Tue Jan 10 01:58:31 2006
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Date: Mon, 9 Jan 2006 22:58:18 -0700
From: Michael Fuhr <mike@fuhr.org>
To: Robert Creager <Robert_Creager@LogicalChaos.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
Message-ID: <20060110055818.GA55076@winnie.fuhr.org>
References: <20060109212338.6420af12@thunder.logicalchaos.org>
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On Mon, Jan 09, 2006 at 09:23:38PM -0700, Robert Creager wrote:
> I'm working with a query to get more info out with a join.  The base
> query works great speed wise because of index usage.  When the join is
> tossed in, the index is no longer used, so the query performance tanks.

The first query you posted returns 285 rows and the second returns
over one million; index usage aside, that difference surely accounts
for a performance penalty.  And as is often pointed out, index scans
aren't always faster than sequential scans: the more of a table a
query has to fetch, the more likely a sequential scan will be faster.

Have the tables been vacuumed and analyzed?  The planner's estimates
for windspeed are pretty far off, which could be affecting the query
plan:

>         ->  Sort  (cost=12997.68..13157.98 rows=64120 width=28) (actual time=2286.155..2286.450 rows=284 loops=1)
>               Sort Key: date_part('doy'::text, unmunge_time(windspeed.time_group))
>               ->  Seq Scan on windspeed  (cost=0.00..7878.18 rows=64120 width=28) (actual time=2279.275..2285.271 rows=284 loops=1)
>                     Filter: (unmunge_time(time_group) > (now() - '24:00:00'::interval))

That's a small amount of the total query time, however, so although
an index scan might help it probably won't provide the big gain
you're looking for.

Have you done any tests with enable_seqscan disabled?  That'll show
whether an index or bitmap scan would be faster.  And have you
verified that the join condition is correct?  Should the query be
returning over a million rows?

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Tue Jan 10 03:46:33 2006
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Date: Tue, 10 Jan 2006 08:46:39 +0100
From: Alessandro Baretta <a.baretta@barettadeit.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>,
	pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong statistics!
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Tom Lane wrote:
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
> 
>>Tom Lane wrote:
>>
>>>I'm curious to see how many rows the planner thinks this will produce,
>>>and whether it will use the index or not.
>>dmd-freerp-1-alex=# EXPLAIN ANALYZE SELECT * FROM articolo WHERE 
>>articolo.xdbs_modified > '2006-01-08 18:25:00+01';
>>                                                                 QUERY PLAN
>>-------------------------------------------------------------------------------------------------------------------------------------------
>>  Index Scan using articolo_modified_index on articolo  (cost=0.00..3914.91 
>>rows=17697 width=653) (actual time=0.032..0.032 rows=0 loops=1)
>>    Index Cond: (xdbs_modified > '2006-01-08 18:25:00'::timestamp without time zone)
>>  Total runtime: 0.150 ms
>>(3 rows)
> 
> 
> Well, there's your problem: 17697 rows estimated vs 0 actual.  With a
> closer row estimate it would've probably done the right thing for the
> join problem.

Hmmm, what you are telling me is very interesting, Tom. So, let me see if I got 
this straight: the first 'rows=... in the result from EXPLAIN ANALYZE gives me 
estimates, while the second gives the actual cardinality of the selected record 
set. Correct? If this is true, two questions arise: why is the estimated number 
of rows completele wrong, and why, given such a large estimated record set does 
PostgreSQL schedule an Index Scan as opposed to a Seq Scan?


 >
 > How many rows are really in the table, anyway?  Could we see the
 > pg_stats row for articolo.xdbs_modified?

dmd-freerp-1-alex=# select count(*) from articolo;
  count
-------
  53091
(1 row)

dmd-freerp-1-alex=# explain analyze select * from articolo;
                                                    QUERY PLAN
-----------------------------------------------------------------------------------------------------------------
  Seq Scan on articolo  (cost=0.00..1439.91 rows=53091 width=653) (actual 
time=0.013..151.189 rows=53091 loops=1)
  Total runtime: 295.152 ms
(2 rows)

Now let me get the pg_stats for xdbs_modified.

dmd-freerp-1-alex=# select * from pg_stats where tablename = 'articolo' and 
attname = 'xdbs_modified';
  schemaname | tablename |    attname    | null_frac | avg_width | n_distinct | 
        most_common_vals        | most_common_freqs | histogram_bounds | correlation
------------+-----------+---------------+-----------+-----------+------------+--------------------------------+-------------------+------------------+-------------
  public     | articolo  | xdbs_modified |         0 |         8 |          1 | 
{"2006-01-10 08:12:58.605327"} | {1}               |       |           1
(1 row)

For sake of simplicity I have re-timestamped all tuples in the table with the 
current timestamp, as you can see above. Now, obviously, the planner must 
estimate ~0 rows for queries posing a selection condition on xdbs_modified, for 
any value other than "2006-01-10 08:12:58.605327". Let me try selecting from 
articolo first.

dmd-freerp-1-alex=# EXPLAIN ANALYZE SELECT * FROM articolo WHERE 
articolo.xdbs_modified > '2006-01-10 18:25:00+01';
                                                              QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
  Index Scan using articolo_modified_index on articolo  (cost=0.00..2.01 rows=1 
width=653) (actual time=0.139..0.139 rows=0 loops=1)
    Index Cond: (xdbs_modified > '2006-01-10 18:25:00'::timestamp without time zone)
  Total runtime: 0.257 ms
(3 rows)

The planner produces a sensible estimate of the number of rows and consequently 
chooses the appropriate query plan. Now, the join.

dmd-freerp-1-alex=# explain analyze SELECT *  FROM articolo JOIN ubicazione 
USING  (id_ente, id_produttore, id_articolo) WHERE articolo.id_ente =  'dmd' AND 
allarme IS NULL AND manutenzione IS NULL AND articolo.xdbs_modified > 
'2006-01-10 18:25:00+01';
 
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Nested Loop  (cost=0.00..5.05 rows=1 width=1146) (actual time=0.043..0.043 
rows=0 loops=1)
    ->  Index Scan using articolo_modified_index on articolo  (cost=0.00..2.02 
rows=1 width=653) (actual time=0.035..0.035 rows=0 loops=1)
          Index Cond: (xdbs_modified > '2006-01-10 18:25:00'::timestamp without 
time zone)
          Filter: (id_ente = 'dmd'::text)
    ->  Index Scan using ubicazione_fkey_articolo on ubicazione 
(cost=0.00..3.02 rows=1 width=536) (never executed)
          Index Cond: (('dmd'::text = ubicazione.id_ente) AND 
("outer".id_produttore = ubicazione.id_produttore) AND ("outer".id_articolo = 
ubicazione.id_articolo))
          Filter: ((allarme IS NULL) AND (manutenzione IS NULL))
  Total runtime: 0.382 ms
(8 rows)

Dear Tom, you're my hero! I have no clue as to how or why the statistics were 
wrong yesterday--as I vacuum-analyzed continuously out of lack of any better 
idea--and I was stupid enough to re-timestamp everything before selecting from 
pg_stats. Supposedly, the timestamps in the table were a random sampling taken 
from the month of December 2005, so that any date in January would be greater 
than all the timestamps in xdbs_modified. There must a bug in the my 
rule/trigger system, which is responsible to maintain these timestamps as 
appropriate.

> 			regards, tom lane
>

Thank you very much Tom and Matteo. Your help has been very precious to me. 
Thanks to your wisdom, my application will now have a 500x speed boost on a very 
common class of queries.

The end result is the following query plan, allowing me to rapidly select only 
the tuples in a join which have changed since the application last updated its 
notion of this dataset.

dmd-freerp-1-alex=# explain analyze SELECT *  FROM articolo JOIN ubicazione 
USING  (id_ente, id_produttore, id_articolo) WHERE articolo.id_ente =  'dmd' AND 
allarme IS NULL AND manutenzione IS NULL AND articolo.xdbs_modified > 
'2006-01-10 18:25:00+01' UNION SELECT * FROM articolo JOIN ubicazione USING 
(id_ente, id_produttore, id_articolo) WHERE articolo.id_ente =  'dmd' AND 
allarme IS NULL AND manutenzione IS NULL AND ubicazione.xdbs_modified > 
'2006-01-10 18:25:00+01';
            QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Unique  (cost=11.13..11.39 rows=2 width=1146) (actual time=0.519..0.519 rows=0 
loops=1)
    ->  Sort  (cost=11.13..11.14 rows=2 width=1146) (actual time=0.512..0.512 
rows=0 loops=1)
          Sort Key: id_ente, id_produttore, id_articolo, bigoid, metadata, 
finalized, xdbs_created, xdbs_modified, barcode, tipo, venditore_id_ente, 
id_prodotto, aggregato_id_ente, aggregato_id_produttore, aggregato_id_articolo, 
descr, url, datasheet, scheda_sicurezza, peso, lunghezza, larghezza, altezza, 
volume, max_strati, um, bigoid, metadata, finalized, xdbs_created, 
xdbs_modified, barcode, tipo, id_magazzino, id_settore, id_area, id_ubicazione, 
flavor, peso_max, lunghezza, larghezza, altezza, volume_max, inventario, 
allarme, manutenzione, quantita, in_prelievo, in_deposito, lotto, scadenza
          ->  Append  (cost=0.00..11.12 rows=2 width=1146) (actual 
time=0.305..0.305 rows=0 loops=1)
                ->  Subquery Scan "*SELECT* 1"  (cost=0.00..5.06 rows=1 
width=1146) (actual time=0.157..0.157 rows=0 loops=1)
                      ->  Nested Loop  (cost=0.00..5.05 rows=1 width=1146) 
(actual time=0.149..0.149 rows=0 loops=1)
                            ->  Index Scan using articolo_modified_index on 
articolo  (cost=0.00..2.02 rows=1 width=653) (actual time=0.142..0.142 rows=0 
loops=1)
                                  Index Cond: (xdbs_modified > '2006-01-10 
18:25:00'::timestamp without time zone)
                                  Filter: (id_ente = 'dmd'::text)
                            ->  Index Scan using ubicazione_fkey_articolo on 
ubicazione  (cost=0.00..3.02 rows=1 width=536) (never executed)
                                  Index Cond: (('dmd'::text = 
ubicazione.id_ente) AND ("outer".id_produttore = ubicazione.id_produttore) AND 
("outer".id_articolo = ubicazione.id_articolo))
                                  Filter: ((allarme IS NULL) AND (manutenzione 
IS NULL))
                ->  Subquery Scan "*SELECT* 2"  (cost=0.00..6.06 rows=1 
width=1146) (actual time=0.137..0.137 rows=0 loops=1)
                      ->  Nested Loop  (cost=0.00..6.05 rows=1 width=1146) 
(actual time=0.131..0.131 rows=0 loops=1)
                            ->  Index Scan using ubicazione_modified_index on 
ubicazione  (cost=0.00..3.02 rows=1 width=536) (actual time=0.123..0.123 rows=0 
loops=1)
                                  Index Cond: (xdbs_modified > '2006-01-10 
18:25:00'::timestamp without time zone)
                                  Filter: ((allarme IS NULL) AND (manutenzione 
IS NULL) AND ('dmd'::text = id_ente))
                            ->  Index Scan using articolo_pkey on articolo 
(cost=0.00..3.02 rows=1 width=653) (never executed)
                                  Index Cond: ((articolo.id_ente = 'dmd'::text) 
AND (articolo.id_produttore = "outer".id_produttore) AND (articolo.id_articolo = 
"outer".id_articolo))
  Total runtime: 1.609 ms
(20 rows)

Since the previous approach used in my application was to select the whole 
relation every time the user needed to access this data, the above result must 
be compared with the following naive one.

dmd-freerp-1-alex=# explain analyze SELECT *  FROM articolo JOIN ubicazione 
USING  (id_ente, id_produttore, id_articolo) WHERE articolo.id_ente =  'dmd' AND 
allarme IS NULL AND manutenzione IS NULL; 
                                     QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
  Nested Loop  (cost=0.00..1014.49 rows=1 width=1146) (actual 
time=0.210..283.272 rows=3662 loops=1)
    ->  Seq Scan on ubicazione  (cost=0.00..1011.45 rows=1 width=536) (actual 
time=0.070..51.223 rows=12036 loops=1)
          Filter: ((allarme IS NULL) AND (manutenzione IS NULL) AND ('dmd'::text 
= id_ente))
    ->  Index Scan using articolo_pkey on articolo  (cost=0.00..3.02 rows=1 
width=653) (actual time=0.008..0.009 rows=0 loops=12036)
          Index Cond: ((articolo.id_ente = 'dmd'::text) AND 
(articolo.id_produttore = "outer".id_produttore) AND (articolo.id_articolo = 
"outer".id_articolo))
  Total runtime: 292.544 ms
(6 rows)

This amounts to a ~200x speedup for the end user.

Alex

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From pgsql-performance-owner@postgresql.org  Tue Jan 10 05:08:33 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Andrea Arcangeli <andrea@cpushare.com>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
References: <20060110014447.GB18474@opteron.random>
	<24021.1136858688@sss.pgh.pa.us>
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Hi,

> I did just think of something we could improve though.  The pattern
> selectivity code doesn't make any use of the statistics about "most
> common values".  For a constant pattern, we could actually apply the
> pattern test with each common value and derive answers that are exact
> for the portion of the population represented by the most-common-values
> list.  If the MCV list covers a large fraction of the population then
> this would be a big leg up in accuracy.  Dunno if that applies to your
> particular case or not, but it seems worth doing ...

This reminds me what I did in a patch which is currently on hold for the 
next release:

http://momjian.postgresql.org/cgi-bin/pgpatches_hold
http://candle.pha.pa.us/mhonarc/patches_hold/msg00026.html

The patch was addressing a similar issue when using ltree <@ and @> 
operator on an unbalanced tree.


Best regards
--
Matteo Beccati
http://phpadsnew.com
http://phppgads.com

From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:31:35 2006
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Subject: Re: help tuning queries on large database
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At 12:23 PM 1/9/2006, peter royal wrote:

>On Jan 8, 2006, at 4:35 PM, Ron wrote:
>>>Areca ARC-1220 8-port PCI-E controller
>>
>>Make sure you have 1GB or 2GB of cache.  Get the battery backup and
>>set the cache for write back rather than write through.
>
>The card we've got doesn't have a SODIMM socket, since its only an 
>8- port card.  My understanding was that was cache used when writing?
Trade in your 8 port ARC-1220 that doesn't support 1-2GB of cache for 
a 12, 16, or 24 port Areca one that does.  It's that important.

Present generation SATA2 HDs should average ~50MBps raw ASTR.  The 
Intel IOP333 DSP on the ARC's is limited to 800MBps, so that's your 
limit per card.  That's 16 SATA2 HD's operating in parallel (16HD 
RAID 0, 17 HD RAID 5, 32 HD RAID 10).

Next generation 2.5" form factor 10Krpm SAS HD's due to retail in 
2006 are supposed to average ~90MBps raw ASTR.  8 such HDs in 
parallel per ARC-12xx will be the limit.

Side Note: the PCI-Ex8 bus on the 12xx cards is good for ~1.6GBps 
RWPB, so I expect Areca is going to be upgrading this controller to 
at least 2x, if not 4x (would require replacing the x8 bus with a x16 
bus), the bandwidth at some point.

A PCI-Ex16 bus is good for ~3.2GBps RWPB, so if you have the slots 4 
such populated ARC cards will max out a PCI-Ex16 bus.

In your shoes, I think I would recommend replacing your 8 port 
ARC-1220 with a 12 port ARC-1230 with 1-2GB of battery backed cache 
and planning to get more of them as need arises.


>>A 2.6.12 or later based Linux distro should have NO problems using
>>more than 4GB or RAM.
>
>Upgraded the kernel to 2.6.15, then we were able to set the BIOS
>option for the 'Memory Hole' to 'Software' and it saw all 4G (under
>2.6.11 we got a kernel panic with that set)
There are some other kernel tuning params that should help memory and 
physical IO performance.  Talk to a Linux kernel guru to get the 
correct advice specific to your installation and application.


It should be noted that there are indications of some major 
inefficiencies in pg's IO layer that make it compute bound under some 
circumstances before it becomes IO bound.  These may or may not cause 
trouble for you as you keep pushing the envelope for maximum IO performance.


With the kind of work you are doing and we are describing, I'm sure 
you can have a _very_ zippy system.

Ron



From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:31:46 2006
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Date: Tue, 10 Jan 2006 12:41:27 -0200
From: "Charles A. Landemaine" <landemaine@gmail.com>
To: pgsql-performance@postgresql.org
Subject: How to handle a large DB and simultaneous accesses?
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Hello,

I have to develop a companies search engine (looks like the Yellow
pages). We're using PostgreSQL at the company, and the initial DB is
2GB large, as it
has companies from the entire world, with a fair amount of information.

What reading do you suggest so that we can develop the search engine
core, in order that the result pages show up instantly, no matter the
heavy load and
the DB size. The DB is 2GB but should grow to up to 10GB in 2 years,
and there should be 250,000 unique visitors per month by the end of
the year.

Are there special techniques? Maybe there's a way to sort of cache
search results? We're using PHP5 + phpAccelerator.
Thanks,

--
Charles A. Landemaine.

From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:33:33 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,  pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
References: <20060110014447.GB18474@opteron.random>
	<24021.1136858688@sss.pgh.pa.us>
	<20060110022303.GA20168@opteron.random>
	<24372.1136861684@sss.pgh.pa.us>
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From: Greg Stark <gsstark@mit.edu>
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Andrea Arcangeli <andrea@cpushare.com> writes:

> Fixing this with proper stats would be great indeed. What would be the
> most common value for the kernel_version? You can see samples of the
> kernel_version here http://klive.cpushare.com/2.6.15/ .  That's the
> string that is being searched against both PREEMPT and SMP.

Try something like this where attname is the column name and tablename is,
well, the tablename:

db=> select most_common_vals from pg_stats where tablename = 'region' and attname = 'province';
 most_common_vals 
------------------
 {ON,NB,QC,BC}

Note that there's a second column most_common_freqs and to do this would
really require doing a weighted average based on the frequencies.

-- 
greg


From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:33:20 2006
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Date: Tue, 10 Jan 2006 08:17:05 -0700
From: Robert Creager <Robert_Creager@LogicalChaos.org>
To: Michael Fuhr <mike@fuhr.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
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	<20060110055818.GA55076@winnie.fuhr.org>
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When grilled further on (Mon, 9 Jan 2006 22:58:18 -0700),
Michael Fuhr <mike@fuhr.org> confessed:

> On Mon, Jan 09, 2006 at 09:23:38PM -0700, Robert Creager wrote:
> > I'm working with a query to get more info out with a join.  The base
> > query works great speed wise because of index usage.  When the join is
> > tossed in, the index is no longer used, so the query performance tanks.
>=20
> The first query you posted returns 285 rows and the second returns
> over one million; index usage aside, that difference surely accounts
> for a performance penalty.  And as is often pointed out, index scans
> aren't always faster than sequential scans: the more of a table a
> query has to fetch, the more likely a sequential scan will be faster.

Thanks for pointing out the obvious that I missed.  Too much data in the se=
cond query.  It's supposed to match (row wise) what was returned from the f=
irst query.

Just ignore me for now...

Thanks,
Rob

--=20
 08:15:24 up 3 days, 42 min,  9 users,  load average: 2.07, 2.20, 2.25
Linux 2.6.12-12-2 #4 SMP Tue Jan 3 19:56:19 MST 2006

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From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:32:57 2006
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To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: Matteo Beccati <php@beccati.com>, pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong statistics! 
In-reply-to: <43C3665F.5020106@barettadeit.com> 
References: <43C26A5F.7040702@barettadeit.com> <43C27AFA.7060604@beccati.com>
	<43C28DEA.60801@barettadeit.com> <6719.1136832065@sss.pgh.pa.us>
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Comments: In-reply-to Alessandro Baretta <a.baretta@barettadeit.com>
	message dated "Tue, 10 Jan 2006 08:46:39 +0100"
Date: Tue, 10 Jan 2006 10:22:59 -0500
Message-ID: <29702.1136906579@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
> I have no clue as to how or why the statistics were wrong
> yesterday--as I vacuum-analyzed continuously out of lack of any better
> idea--and I was stupid enough to re-timestamp everything before
> selecting from pg_stats.

Too bad.  I would be interested to find out how, if the stats were
up-to-date, the thing was still getting the row estimate so wrong.
If you manage to get the database back into its prior state please
do send along the pg_stats info.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:32:36 2006
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From: Andrea Arcangeli <andrea@cpushare.com>
To: Greg Stark <gsstark@mit.edu>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
Message-ID: <20060110152720.GL15897@opteron.random>
References: <20060110014447.GB18474@opteron.random>
	<24021.1136858688@sss.pgh.pa.us>
	<20060110022303.GA20168@opteron.random>
	<24372.1136861684@sss.pgh.pa.us>
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On Tue, Jan 10, 2006 at 10:11:18AM -0500, Greg Stark wrote:
> 
> Andrea Arcangeli <andrea@cpushare.com> writes:
> 
> > Fixing this with proper stats would be great indeed. What would be the
> > most common value for the kernel_version? You can see samples of the
> > kernel_version here http://klive.cpushare.com/2.6.15/ .  That's the
> > string that is being searched against both PREEMPT and SMP.
> 
> Try something like this where attname is the column name and tablename is,
> well, the tablename:
> 
> db=> select most_common_vals from pg_stats where tablename = 'region' and attname = 'province';
>  most_common_vals 
> ------------------
>  {ON,NB,QC,BC}

Thanks for the info!

klive=> select most_common_vals from pg_stats where tablename = 'klive' and attname = 'kernel_version';
                                                                                                                                                                            most_common_vals                                                                                                                                                                            
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"#1 Tue Sep 13 14:56:15 UTC 2005","#1 Fri Aug 19 11:58:59 UTC 2005","#7 SMP Fri Oct 7 15:56:41 CEST 2005","#1 SMP Fri Aug 19 11:58:59 UTC 2005","#2 Thu Sep 22 15:58:44 CEST 2005","#1 Fri Sep 23 15:32:21 GMT 2005","#1 Fri Oct 21 03:46:55 EDT 2005","#1 Sun Sep 4 13:45:32 CEST 2005","#5 PREEMPT Mon Nov 21 17:53:59 EET 2005","#1 Wed Sep 28 19:15:10 EDT 2005"}
(1 row)

klive=> select most_common_freqs from pg_stats where tablename = 'klive' and attname = 'kernel_version';
                                     most_common_freqs                                     
-------------------------------------------------------------------------------------------
 {0.0133333,0.0116667,0.011,0.009,0.00733333,0.00666667,0.00633333,0.006,0.006,0.00566667}
(1 row)

klive=> 

There's only one preempt near the end, not sure if it would work?

From pgsql-performance-owner@postgresql.org  Tue Jan 10 11:47:15 2006
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To: Andrea Arcangeli <andrea@cpushare.com>
cc: Greg Stark <gsstark@mit.edu>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
In-reply-to: <20060110152720.GL15897@opteron.random> 
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	<24021.1136858688@sss.pgh.pa.us>
	<20060110022303.GA20168@opteron.random>
	<24372.1136861684@sss.pgh.pa.us>
	<20060110034721.GC20168@opteron.random>
	<87y81oyv6x.fsf@stark.xeocode.com>
	<20060110152720.GL15897@opteron.random>
Comments: In-reply-to Andrea Arcangeli <andrea@cpushare.com>
	message dated "Tue, 10 Jan 2006 16:27:20 +0100"
Date: Tue, 10 Jan 2006 10:46:53 -0500
Message-ID: <152.1136908013@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Andrea Arcangeli <andrea@cpushare.com> writes:
> There's only one preempt near the end, not sure if it would work?

Not with that data, but maybe if you increased the statistics target for
the column to 100 or so, you'd catch enough values to get reasonable
results.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 10 13:50:01 2006
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To: Matteo Beccati <php@beccati.com>
cc: Andrea Arcangeli <andrea@cpushare.com>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
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Comments: In-reply-to Matteo Beccati <php@beccati.com>
	message dated "Tue, 10 Jan 2006 10:08:45 +0100"
Date: Tue, 10 Jan 2006 12:49:55 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Matteo Beccati <php@beccati.com> writes:
>> I did just think of something we could improve though.  The pattern
>> selectivity code doesn't make any use of the statistics about "most
>> common values".  For a constant pattern, we could actually apply the
>> pattern test with each common value and derive answers that are exact
>> for the portion of the population represented by the most-common-values
>> list.

> This reminds me what I did in a patch which is currently on hold for the 
> next release:

I've applied a patch to make patternsel() compute the exact result for
the MCV list, and use its former heuristics only for the portion of the
column population not included in the MCV list.

After finishing that work it occurred to me that we could go a step
further: if the MCV list accounts for a substantial fraction of the
population, we could assume that the MCV list is representative of the
whole population, and extrapolate the pattern's selectivity over the MCV
list to the whole population instead of using the existing heuristics at
all.  In a situation like Andreas' example this would win big, although
you can certainly imagine cases where it would lose too.

Any thoughts about this?  What would be a reasonable threshold for
"substantial fraction"?  It would probably make sense to have different
thresholds depending on whether the pattern is left-anchored or not,
since the range heuristic only works for left-anchored patterns.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 10 18:06:38 2006
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Subject: Re: NOT LIKE much faster than LIKE?
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
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On Tue, 2006-01-10 at 12:49 -0500, Tom Lane wrote:
> Matteo Beccati <php@beccati.com> writes:
> >> I did just think of something we could improve though.  The pattern
> >> selectivity code doesn't make any use of the statistics about "most
> >> common values".  For a constant pattern, we could actually apply the
> >> pattern test with each common value and derive answers that are exact
> >> for the portion of the population represented by the most-common-values
> >> list.
> 
> > This reminds me what I did in a patch which is currently on hold for the 
> > next release:
> 
> I've applied a patch to make patternsel() compute the exact result for
> the MCV list, and use its former heuristics only for the portion of the
> column population not included in the MCV list.

I think its OK to use the MCV, but I have a problem with the current
heuristics: they only work for randomly generated strings, since the
selectivity goes down geometrically with length. That doesn't match most
languages where one and two syllable words are extremely common and
longer ones much less so. A syllable can be 1-2 chars long, so any
search string of length 1-4 is probably equally likely, rather than
reducing in selectivity based upon length. So I think part of the
problem is the geometrically reducing selectivity itself.

> After finishing that work it occurred to me that we could go a step
> further: if the MCV list accounts for a substantial fraction of the
> population, we could assume that the MCV list is representative of the
> whole population, and extrapolate the pattern's selectivity over the MCV
> list to the whole population instead of using the existing heuristics at
> all.  In a situation like Andreas' example this would win big, although
> you can certainly imagine cases where it would lose too.

I don't think that can be inferred with any confidence, unless a large
proportion of the MCV list were itself selected. Otherwise it might
match only a single MCV that just happens to have a high proportion,
then we assume all others have the same proportion. The calculation is
related to Ndistinct, in some ways.

> Any thoughts about this?  What would be a reasonable threshold for
> "substantial fraction"?  It would probably make sense to have different
> thresholds depending on whether the pattern is left-anchored or not,
> since the range heuristic only works for left-anchored patterns.

I don't think you can do this for a low enough substantial fraction to
make this interesting.

I would favour the idea of dynamic sampling using a block sampling
approach; that was a natural extension of improving ANALYZE also. We can
use that approach for things such as LIKE, but also use it for
multi-column single-table and join selectivity.

Best Regards, Simon Riggs



From pgsql-performance-owner@postgresql.org  Tue Jan 10 18:21:37 2006
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To: Simon Riggs <simon@2ndquadrant.com>
cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
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Comments: In-reply-to Simon Riggs <simon@2ndquadrant.com>
	message dated "Tue, 10 Jan 2006 22:06:36 +0000"
Date: Tue, 10 Jan 2006 17:21:25 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Simon Riggs <simon@2ndquadrant.com> writes:
> I think its OK to use the MCV, but I have a problem with the current
> heuristics: they only work for randomly generated strings, since the
> selectivity goes down geometrically with length.

We could certainly use a less aggressive curve for that.  You got a
specific proposal?

>> After finishing that work it occurred to me that we could go a step
>> further: if the MCV list accounts for a substantial fraction of the
>> population, we could assume that the MCV list is representative of the
>> whole population, and extrapolate the pattern's selectivity over the MCV
>> list to the whole population instead of using the existing heuristics at
>> all.  In a situation like Andreas' example this would win big, although
>> you can certainly imagine cases where it would lose too.

> I don't think that can be inferred with any confidence, unless a large
> proportion of the MCV list were itself selected. Otherwise it might
> match only a single MCV that just happens to have a high proportion,
> then we assume all others have the same proportion.

Well, of course it can't be inferred "with confidence".  Sometimes
you'll win and sometimes you'll lose.  The question is, is this a
better heuristic than what we use otherwise?  The current estimate
for non-anchored patterns is really pretty crummy, and even with a
less aggressive length-vs-selectivity curve it's not going to be great.

Another possibility is to merge the two estimates somehow.

> I would favour the idea of dynamic sampling using a block sampling
> approach; that was a natural extension of improving ANALYZE also.

One thing at a time please.  Obtaining better statistics is one issue,
but the one at hand here is what to do given particular statistics.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 10 19:36:47 2006
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Subject: Re: NOT LIKE much faster than LIKE?
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
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On Tue, 2006-01-10 at 17:21 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > I think its OK to use the MCV, but I have a problem with the current
> > heuristics: they only work for randomly generated strings, since the
> > selectivity goes down geometrically with length.
> 
> We could certainly use a less aggressive curve for that.  You got a
> specific proposal?

I read some research not too long ago that showed a frequency curve of
words by syllable length. I'll dig that out tomorrow.

> > I would favour the idea of dynamic sampling using a block sampling
> > approach; that was a natural extension of improving ANALYZE also.
> 
> One thing at a time please.  Obtaining better statistics is one issue,
> but the one at hand here is what to do given particular statistics.

I meant use the same sampling approach as I was proposing for ANALYZE,
but do this at plan time for the query. That way we can apply the
function directly to the sampled rows and estimate selectivity. 

I specifically didn't mention that in the Ndistinct discussion because I
didn't want to confuse the subject further, but the underlying block
sampling method would be identical, so the code is already almost
there...we just need to eval the RestrictInfo against the sampled
tuples.

Best Regards, Simon Riggs




From pgsql-performance-owner@postgresql.org  Tue Jan 10 20:29:23 2006
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	10 Jan 2006 16:28:06 -0800
Subject: Re: help tuning queries on large database
From: Mark Lewis <mark.lewis@mir3.com>
To: Ron <rjpeace@earthlink.net>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <7.0.1.0.2.20060108160633.026bd358@earthlink.net>
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Ron,

A few days back you mentioned:

> Upgrade your kernel to at least  2.6.12
> There's a known issue with earlier versions of the 2.6.x kernel and 
> 64b CPUs like the Opteron.  See kernel.org for details.
> 

I did some searching and couldn't find any obvious mention of this issue
(I gave up after searching through the first few hundred instances of
"64" in the 2.6.12 changelog).

Would you mind being a little more specific about which issue you're
talking about?  We're about to deploy some new 16GB RAM Opteron DB
servers and I'd like to check and make sure RH backported whatever the
fix was to their current RHEL4 kernel.

Thanks,
Mark Lewis

From pgsql-performance-owner@postgresql.org  Tue Jan 10 23:06:11 2006
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From: "Dave Dutcher" <dave@tridecap.com>
To: <pgsql-performance@postgresql.org>
Subject: Left Join Performance vs Inner Join Performance
Date: Tue, 10 Jan 2006 20:06:08 -0600
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Hello,
 
I have an inner join query that runs fast, but I when I change to a left
join the query runs 96 times slower.  I wish I could always do an inner
join, but there are rare times when there isn't data in the right hand
table.  I could expect a small performance hit, but the difference is so
large I figure I must be doing something wrong.  What I think is the
strangest is how similar the two query plans are.
 
Query (inner join version, just replace inner with left for other
version):
select 
p.owner_trader_id, p.strategy_id, m.last, m.bid, m.ask
from 
om_position p inner join om_instrument_mark m on m.instrument_id =
p.instrument_id and m.data_source_id = 5 and m.date = '2005-02-03' 
where p.as_of_date = '2005-02-03' and p.fund_id = 'TRIDE' and
p.owner_trader_id = 'tam4' and p.strategy_id = 'BASKET1'
 
Query plan for inner join:
Nested Loop  (cost=0.00..176.99 rows=4 width=43) (actual
time=0.234..14.182 rows=193 loops=1)
  ->  Index Scan using as_of_date_om_position_index on om_position p
(cost=0.00..68.26 rows=19 width=20) (actual time=0.171..5.210 rows=193
loops=1)
        Index Cond: (as_of_date = '2005-02-03'::date)"
        Filter: (((fund_id)::text = 'TRIDE'::text) AND
((owner_trader_id)::text = 'tam4'::text) AND ((strategy_id)::text =
'BASKET1'::text))
  ->  Index Scan using om_instrument_mark_pkey on om_instrument_mark m
(cost=0.00..5.71 rows=1 width=31) (actual time=0.028..0.032 rows=1
loops=193)
        Index Cond: ((m.instrument_id = "outer".instrument_id) AND
(m.data_source_id = 5) AND (m.date = '2005-02-03'::date))
Total runtime: 14.890 ms
 
Query plan for left join:
Nested Loop Left Join  (cost=0.00..7763.36 rows=19 width=43) (actual
time=3.005..1346.308 rows=193 loops=1)
  ->  Index Scan using as_of_date_om_position_index on om_position p
(cost=0.00..68.26 rows=19 width=20) (actual time=0.064..6.654 rows=193
loops=1)
        Index Cond: (as_of_date = '2005-02-03'::date)
        Filter: (((fund_id)::text = 'TRIDE'::text) AND
((owner_trader_id)::text = 'tam4'::text) AND ((strategy_id)::text =
'BASKET1'::text))
  ->  Index Scan using om_instrument_mark_pkey on om_instrument_mark m
(cost=0.00..404.99 rows=1 width=31) (actual time=3.589..6.919 rows=1
loops=193)
        Index Cond: (m.instrument_id = "outer".instrument_id)
        Filter: ((data_source_id = 5) AND (date = '2005-02-03'::date))
Total runtime: 1347.159 ms
 
 
Table Definitions:
CREATE TABLE om_position
(
  fund_id varchar(10) NOT NULL DEFAULT ''::character varying,
  owner_trader_id varchar(10) NOT NULL DEFAULT ''::character varying,
  strategy_id varchar(30) NOT NULL DEFAULT ''::character varying,
  instrument_id int4 NOT NULL DEFAULT 0,
  as_of_date date NOT NULL DEFAULT '0001-01-01'::date,
  pos numeric(22,9) NOT NULL DEFAULT 0.000000000,
  cf_account_id int4 NOT NULL DEFAULT 0,
  cost numeric(22,9) NOT NULL DEFAULT 0.000000000,
  CONSTRAINT om_position_pkey PRIMARY KEY (fund_id, owner_trader_id,
strategy_id, cf_account_id, instrument_id, as_of_date),
  CONSTRAINT "$1" FOREIGN KEY (strategy_id)
      REFERENCES om_strategy (strategy_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT "$2" FOREIGN KEY (fund_id)
      REFERENCES om_fund (fund_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT "$3" FOREIGN KEY (cf_account_id)
      REFERENCES om_cf_account (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT "$4" FOREIGN KEY (owner_trader_id)
      REFERENCES om_trader (trader_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
) 
WITH OIDS;
CREATE INDEX as_of_date_om_position_index
  ON om_position
  USING btree
  (as_of_date);
 
CREATE TABLE om_instrument_mark
(
  instrument_id int4 NOT NULL DEFAULT 0,
  data_source_id int4 NOT NULL DEFAULT 0,
  date date NOT NULL DEFAULT '0001-01-01'::date,
  "last" numeric(22,9) NOT NULL DEFAULT 0.000000000,
  bid numeric(22,9) NOT NULL DEFAULT 0.000000000,
  ask numeric(22,9) NOT NULL DEFAULT 0.000000000,
  "comment" varchar(150) NOT NULL DEFAULT ''::character varying,
  trader_id varchar(10) NOT NULL DEFAULT 'auto'::character varying,
  CONSTRAINT om_instrument_mark_pkey PRIMARY KEY (instrument_id,
data_source_id, date),
  CONSTRAINT "$1" FOREIGN KEY (instrument_id)
      REFERENCES om_instrument (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT "$2" FOREIGN KEY (data_source_id)
      REFERENCES om_data_source (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT om_instrument_mark_trader_id_fkey FOREIGN KEY (trader_id)
      REFERENCES om_trader (trader_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
) 
WITH OIDS;
 
Thanks for any help
 

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<body lang=3DEN-US link=3Dblue vlink=3Dpurple =
style=3D'tab-interval:.5in'>

<div class=3DSection1>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Hello,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>I have an inner join query that runs fast, but I when =
I
change to a left join the query <span class=3DGramE>runs</span> 96 times =
slower.<span
style=3D'mso-spacerun:yes'>&nbsp; </span>I wish I could always do an =
inner join,
but there are rare times when there isn&#8217;t data in the right hand
table.<span style=3D'mso-spacerun:yes'>&nbsp; </span>I could expect a =
small
performance hit, but the difference is so large I figure I must be doing
something wrong.<span style=3D'mso-spacerun:yes'>&nbsp; </span>What I =
think is
the strangest is how similar the two query plans =
are.<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Query (inner join version, just replace inner with =
left for
other version):<o:p></o:p></span></font></p>

<p class=3DMsoNormal><span class=3DGramE><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>select</span></font></span><=
font
size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'> =
<o:p></o:p></span></font></p>

<p class=3DMsoNormal><span class=3DSpellE><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>p.owner_trader_id</span></fo=
nt></span><font
size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'>, <span
class=3DSpellE>p.strategy_id</span>, <span class=3DSpellE>m.last</span>, =
<span
class=3DSpellE>m.bid</span>, <span =
class=3DSpellE>m.ask</span><o:p></o:p></span></font></p>

<p class=3DMsoNormal><span class=3DGramE><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>from</span></font></span><fo=
nt
size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'> =
<o:p></o:p></span></font></p>

<p class=3DMsoNormal><span class=3DSpellE><span class=3DGramE><font =
size=3D2
face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'>om_position</span></font></s=
pan></span><font
size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'> p inner
join <span class=3DSpellE>om_instrument_mark</span> m on <span =
class=3DSpellE>m.instrument_id</span>
=3D <span class=3DSpellE>p.instrument_id</span> and <span =
class=3DSpellE>m.data_source_id</span>
=3D 5 and <span class=3DSpellE>m.date</span> =3D '2005-02-03' =
<o:p></o:p></span></font></p>

<p class=3DMsoNormal><span class=3DGramE><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>where</span></font></span><f=
ont
size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial'> <span
class=3DSpellE>p.as_of_date</span> =3D '2005-02-03' and <span =
class=3DSpellE>p.fund_id</span>
=3D 'TRIDE' and <span class=3DSpellE>p.owner_trader_id</span> =3D 'tam4' =
and <span
class=3DSpellE>p.strategy_id</span> =3D =
'BASKET1'<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Query plan for inner =
join:<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Nested <span class=3DGramE>Loop<span
style=3D'mso-spacerun:yes'>&nbsp; </span>(</span>cost=3D0.00..176.99 =
rows=3D4
width=3D43) (actual time=3D0.234..14.182 rows=3D193 =
loops=3D1)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>-<span
class=3DGramE>&gt;<span style=3D'mso-spacerun:yes'>&nbsp; =
</span>Index</span> Scan
using <span class=3DSpellE>as_of_date_om_position_index</span> on <span
class=3DSpellE>om_position</span> p<span =
style=3D'mso-spacerun:yes'>&nbsp;
</span>(cost=3D0.00..68.26 rows=3D19 width=3D20) (actual =
time=3D0.171..5.210 rows=3D193
loops=3D1)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>Index
<span class=3DSpellE>Cond</span>: (<span =
class=3DSpellE>as_of_date</span> =3D
'2005-02-03':<span =
class=3DGramE>:date</span>)&quot;<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Filter: (((<span class=3DSpellE>fund_id</span>)::text =3D '<span
class=3DSpellE>TRIDE'::text</span>) AND ((<span =
class=3DSpellE>owner_trader_id</span>)::text
=3D 'tam4'::text) AND ((<span class=3DSpellE>strategy_id</span>)::text =
=3D
'BASKET1'::text))<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>-<span
class=3DGramE>&gt;<span style=3D'mso-spacerun:yes'>&nbsp; =
</span>Index</span> Scan
using <span class=3DSpellE>om_instrument_mark_pkey</span> on <span =
class=3DSpellE>om_instrument_mark</span>
m<span style=3D'mso-spacerun:yes'>&nbsp; </span>(cost=3D0.00..5.71 =
rows=3D1 width=3D31)
(actual time=3D0.028..0.032 rows=3D1 =
loops=3D193)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Index <span class=3DSpellE>Cond</span>: ((<span =
class=3DSpellE>m.instrument_id</span>
=3D &quot;<span class=3DSpellE>outer&quot;.instrument_id</span>) AND =
(<span
class=3DSpellE>m.data_source_id</span> =3D 5) AND (<span =
class=3DSpellE>m.date</span>
=3D '2005-02-03':<span =
class=3DGramE>:date</span>))<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Total runtime: 14.890 ms<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Query plan for left =
join:<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Nested Loop Left <span class=3DGramE>Join<span
style=3D'mso-spacerun:yes'>&nbsp; </span>(</span>cost=3D0.00..7763.36 =
rows=3D19
width=3D43) (actual time=3D3.005..1346.308 rows=3D193 =
loops=3D1)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>-<span
class=3DGramE>&gt;<span style=3D'mso-spacerun:yes'>&nbsp; =
</span>Index</span> Scan
using <span class=3DSpellE>as_of_date_om_position_index</span> on <span
class=3DSpellE>om_position</span> p<span =
style=3D'mso-spacerun:yes'>&nbsp;
</span>(cost=3D0.00..68.26 rows=3D19 width=3D20) (actual =
time=3D0.064..6.654 rows=3D193
loops=3D1)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Index <span class=3DSpellE>Cond</span>: (<span =
class=3DSpellE>as_of_date</span>
=3D '2005-02-03':<span =
class=3DGramE>:date</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Filter: (((<span class=3DSpellE>fund_id</span>)::text =3D '<span
class=3DSpellE>TRIDE'::text</span>) AND ((<span =
class=3DSpellE>owner_trader_id</span>)::text
=3D 'tam4'::text) AND ((<span class=3DSpellE>strategy_id</span>)::text =
=3D
'BASKET1'::text))<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>-<span
class=3DGramE>&gt;<span style=3D'mso-spacerun:yes'>&nbsp; =
</span>Index</span> Scan
using <span class=3DSpellE>om_instrument_mark_pkey</span> on <span =
class=3DSpellE>om_instrument_mark</span>
m<span style=3D'mso-spacerun:yes'>&nbsp; </span>(cost=3D0.00..404.99 =
rows=3D1
width=3D31) (actual time=3D3.589..6.919 rows=3D1 =
loops=3D193)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Index <span class=3DSpellE>Cond</span>: (<span =
class=3DSpellE>m.instrument_id</span>
=3D &quot;<span =
class=3DSpellE>outer&quot;.instrument_id</span>)<o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span>Filter: ((<span class=3DSpellE>data_source_id</span> =3D 5) AND =
(date =3D
'2005-02-03':<span =
class=3DGramE>:date</span>))<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Total runtime: 1347.159 =
ms<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Table Definitions:<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>CREATE TABLE <span =
class=3DSpellE>om_position</span><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>(<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE><span class=3DGramE>fund_id</span></span> <span =
class=3DSpellE>varchar</span>(10)
NOT NULL DEFAULT ''::character varying,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE><span class=3DGramE>owner_trader_id</span></span> <span
class=3DSpellE>varchar</span>(10) NOT NULL DEFAULT ''::character =
varying,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE><span class=3DGramE>strategy_id</span></span> <span =
class=3DSpellE>varchar</span>(30)
NOT NULL DEFAULT ''::character varying,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE>instrument_id</span> int4 NOT NULL DEFAULT =
0,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE><span class=3DGramE>as_of_date</span></span> date NOT =
NULL DEFAULT
'0001-01-01'::date,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DGramE>pos</span> numeric(22,9) NOT NULL DEFAULT =
0.000000000,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE>cf_account_id</span> int4 NOT NULL DEFAULT =
0,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DGramE>cost</span> numeric(22,9) NOT NULL DEFAULT =
0.000000000,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT <span
class=3DSpellE>om_position_pkey</span> PRIMARY KEY (<span =
class=3DSpellE>fund_id</span>,
<span class=3DSpellE>owner_trader_id</span>, <span =
class=3DSpellE>strategy_id</span>,
<span class=3DSpellE>cf_account_id</span>, <span =
class=3DSpellE>instrument_id</span>,
<span class=3DSpellE>as_of_date</span>),<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT
&quot;$1&quot; FOREIGN KEY (<span =
class=3DSpellE>strategy_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_strategy</span> (<span =
class=3DSpellE>strategy_id</span>) MATCH
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT &quot;$2&quot;
FOREIGN KEY (<span =
class=3DSpellE>fund_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_fund</span> (<span class=3DSpellE>fund_id</span>) =
MATCH SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT
&quot;$3&quot; FOREIGN KEY (<span =
class=3DSpellE>cf_account_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_cf_account</span> (id) MATCH =
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT
&quot;$4&quot; FOREIGN KEY (<span =
class=3DSpellE>owner_trader_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_trader</span> (<span class=3DSpellE>trader_id</span>) =
MATCH
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>) <o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>WITH OIDS;<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>CREATE INDEX <span =
class=3DSpellE>as_of_date_om_position_index</span><o:p></o:p></span></fon=
t></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>ON =
<span
class=3DSpellE>om_position</span><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>USING =
<span
class=3DSpellE>btree</span><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span>(<span
class=3DSpellE>as_of_date</span>);<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>CREATE TABLE <span =
class=3DSpellE>om_instrument_mark</span><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>(<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE>instrument_id</span> int4 NOT NULL DEFAULT =
0,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE>data_source_id</span> int4 NOT NULL DEFAULT =
0,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DGramE>date</span> <span class=3DSpellE>date</span> NOT NULL =
DEFAULT
'0001-01-01'::date,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>&quot;<span
class=3DGramE>last</span>&quot; numeric(22,9) NOT NULL DEFAULT =
0.000000000,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DGramE>bid</span> numeric(22,9) NOT NULL DEFAULT =
0.000000000,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DGramE>ask</span> numeric(22,9) NOT NULL DEFAULT =
0.000000000,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>&quot;<span
class=3DGramE>comment</span>&quot; <span =
class=3DSpellE>varchar</span>(150) NOT
NULL DEFAULT ''::character varying,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; </span><span
class=3DSpellE><span class=3DGramE>trader_id</span></span> <span =
class=3DSpellE>varchar</span>(10)
NOT NULL DEFAULT '<span class=3DSpellE>auto'::character</span> =
varying,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT <span
class=3DSpellE>om_instrument_mark_pkey</span> PRIMARY KEY (<span =
class=3DSpellE>instrument_id</span>,
<span class=3DSpellE>data_source_id</span>, =
date),<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT
&quot;$1&quot; FOREIGN KEY (<span =
class=3DSpellE>instrument_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_instrument</span> (id) MATCH =
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT
&quot;$2&quot; FOREIGN KEY (<span =
class=3DSpellE>data_source_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_data_source</span> (id) MATCH =
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span style=3D'mso-spacerun:yes'>&nbsp; =
</span>CONSTRAINT <span
class=3DSpellE>om_instrument_mark_trader_id_fkey</span> FOREIGN KEY =
(<span
class=3DSpellE>trader_id</span>)<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
</span>REFERENCES <span
class=3DSpellE>om_trader</span> (<span class=3DSpellE>trader_id</span>) =
MATCH
SIMPLE<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><span
style=3D'mso-spacerun:yes'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>ON =
UPDATE NO
ACTION ON DELETE NO ACTION<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>) <o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>WITH OIDS;<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Thanks for any help<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

</div>

</body>

</html>

------=_NextPart_000_0120_01C61621.4C2A99F0--


From pgsql-performance-owner@postgresql.org  Tue Jan 10 23:40:35 2006
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To: Simon Riggs <simon@2ndquadrant.com>
cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE? 
In-reply-to: <1136936205.21025.507.camel@localhost.localdomain> 
References: <20060110014447.GB18474@opteron.random>
	<24021.1136858688@sss.pgh.pa.us>
	<20060110022303.GA20168@opteron.random>
	<24372.1136861684@sss.pgh.pa.us> <43C3799D.5030103@beccati.com>
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	<6398.1136931685@sss.pgh.pa.us>
	<1136936205.21025.507.camel@localhost.localdomain>
Comments: In-reply-to Simon Riggs <simon@2ndquadrant.com>
	message dated "Tue, 10 Jan 2006 23:36:45 +0000"
Date: Tue, 10 Jan 2006 22:40:30 -0500
Message-ID: <7924.1136950830@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Simon Riggs <simon@2ndquadrant.com> writes:
> I meant use the same sampling approach as I was proposing for ANALYZE,
> but do this at plan time for the query. That way we can apply the
> function directly to the sampled rows and estimate selectivity. 

I think this is so unlikely to be a win as to not even be worth spending
any time discussing.  The extra planning time across all queries will
vastly outweigh the occasional improvement in plan choice for some
queries.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 10 23:53:50 2006
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Date: Tue, 10 Jan 2006 19:50:46 -0800 (PST)
From: David Lang <dlang@invendra.net>
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To: "Charles A. Landemaine" <landemaine@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: How to handle a large DB and simultaneous accesses?
In-Reply-To: <e6575a30601100641s61317c63o@mail.gmail.com>
Message-ID: <Pine.LNX.4.62.0601101943020.3019@qnivq.ynat.uz>
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On Tue, 10 Jan 2006, Charles A. Landemaine wrote:

> Hello,
>
> I have to develop a companies search engine (looks like the Yellow
> pages). We're using PostgreSQL at the company, and the initial DB is
> 2GB large, as it
> has companies from the entire world, with a fair amount of information.
>
> What reading do you suggest so that we can develop the search engine
> core, in order that the result pages show up instantly, no matter the
> heavy load and
> the DB size. The DB is 2GB but should grow to up to 10GB in 2 years,
> and there should be 250,000 unique visitors per month by the end of
> the year.
>
> Are there special techniques? Maybe there's a way to sort of cache
> search results? We're using PHP5 + phpAccelerator.
> Thanks,

frankly that is a small enough chunk of data compared to available memory 
sizes that I think your best bet is to plan to have enough ram that you 
only do disk I/O to write and on boot.

a dual socket Opteron system can hold 16G with 2G memory modules (32G as 
4G modules become readily available over the next couple of years). this 
should be enough to keep your data and indexes in ram at all times. if you 
find that other system processes push the data out of ram consider loading 
the data from disk to a ramfs filesystem, just make sure you don't update 
the ram-only copy (or if you do that you have replication setup to 
replicate from the ram copy to a copy on real disks somewhere). depending 
on your load you could go with single core or dual core chips (and the 
cpu's are a small enough cost compared to this much ram that you may as 
well go with the dual core cpu's)

now even with your data in ram you can slow down if your queries, indexes, 
and other settings are wrong, but if performance is important you should 
be able to essentially eliminate disks for databases of this size.

David Lang

From pgsql-performance-owner@postgresql.org  Wed Jan 11 00:38:24 2006
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To: "Dave Dutcher" <dave@tridecap.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Left Join Performance vs Inner Join Performance 
In-reply-to: <011f01c61653$96c509f0$8300a8c0@tridecap.com> 
References: <011f01c61653$96c509f0$8300a8c0@tridecap.com>
Comments: In-reply-to "Dave Dutcher" <dave@tridecap.com>
	message dated "Tue, 10 Jan 2006 20:06:08 -0600"
Date: Tue, 10 Jan 2006 23:38:20 -0500
Message-ID: <8321.1136954300@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Dave Dutcher" <dave@tridecap.com> writes:
> I have an inner join query that runs fast, but I when I change to a left
> join the query runs 96 times slower.

This looks like an issue that is fixed in the latest set of releases,
namely that OUTER JOIN ON conditions that reference only the inner
side of the join weren't getting pushed down into indexquals.  See
thread here:
http://archives.postgresql.org/pgsql-performance/2005-12/msg00134.php
and patches in this and the following messages:
http://archives.postgresql.org/pgsql-committers/2005-12/msg00105.php

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 01:11:25 2006
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From: Robert Creager <Robert_Creager@LogicalChaos.org>
To: Michael Fuhr <mike@fuhr.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
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Ok, I'm back, and in a little better shape.

The query is now correct, but still is slow because of lack of index usage.=
  I don't know how to structure the query correctly to use the index.

Taken individually:

weather=3D# explain analyze select * from doy_agg where doy =3D extract( do=
y from now() );
                                                               QUERY PLAN  =
                                                            =20
---------------------------------------------------------------------------=
-------------------------------------------------------------
 HashAggregate  (cost=3D13750.67..13750.71 rows=3D2 width=3D20) (actual tim=
e=3D123.134..123.135 rows=3D1 loops=3D1)
   ->  Bitmap Heap Scan on readings  (cost=3D25.87..13720.96 rows=3D3962 wi=
dth=3D20) (actual time=3D6.384..116.559 rows=3D4175 loops=3D1)
         Recheck Cond: (date_part('doy'::text, "when") =3D date_part('doy':=
:text, now()))
         ->  Bitmap Index Scan on readings_doy_index  (cost=3D0.00..25.87 r=
ows=3D3962 width=3D0) (actual time=3D5.282..5.282 rows=3D4215 loops=3D1)
               Index Cond: (date_part('doy'::text, "when") =3D date_part('d=
oy'::text, now()))
 Total runtime: 123.366 ms

produces the data:

weather=3D# select * from doy_agg where doy =3D extract( doy from now() );
 doy |  avg_windspeed   | max_windspeed=20
-----+------------------+---------------
  10 | 8.53403056583666 |            59

and:

weather=3D# EXPLAIN ANALYZE
weather-# SELECT *,
weather-# unmunge_time( time_group ) AS time
weather-# FROM minute."windspeed"
weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interval )
weather-# ORDER BY time_group;
                                                                   QUERY PL=
AN                                                                   =20
---------------------------------------------------------------------------=
----------------------------------------------------------------------
 Sort  (cost=3D595.33..595.77 rows=3D176 width=3D28) (actual time=3D4.762..=
4.828 rows=3D283 loops=3D1)
   Sort Key: time_group
   ->  Bitmap Heap Scan on windspeed  (cost=3D2.62..588.76 rows=3D176 width=
=3D28) (actual time=3D0.901..3.834 rows=3D283 loops=3D1)
         Recheck Cond: (unmunge_time(time_group) > (now() - '24:00:00'::int=
erval))
         ->  Bitmap Index Scan on minute_windspeed_unmunge_index  (cost=3D0=
.00..2.62 rows=3D176 width=3D0) (actual time=3D0.745..0.745 rows=3D284 loop=
s=3D1)
               Index Cond: (unmunge_time(time_group) > (now() - '24:00:00':=
:interval))
 Total runtime: 5.108 ms

produces:

 time_group |    min_reading    | max_reading |    avg_reading    |        =
time        =20
------------+-------------------+-------------+-------------------+--------=
-------------
 1136869500 |               0.8 |           6 |  2.62193548387097 | 2006-01=
-09 22:05:00
 1136869800 |                 0 |           3 | 0.406021505376343 | 2006-01=
-09 22:10:00
 1136870100 |                 0 |           5 |              1.68 | 2006-01=
-09 22:15:00
...=20

But I want the composite of the two queries, and I'm stuck on:

weather=3D# EXPLAIN ANALYZE
weather-# SELECT *,
weather-# unmunge_time( time_group ) AS time
weather-# FROM minute."windspeed"
weather-# JOIN doy_agg ON( EXTRACT( doy FROM unmunge_time( time_group ) ) =
=3D doy )
weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interval )
weather-# ORDER BY time_group;
                                                                         QU=
ERY PLAN                                                                   =
      =20
---------------------------------------------------------------------------=
---------------------------------------------------------------------------=
-------
 Sort  (cost=3D153627.67..153628.48 rows=3D322 width=3D48) (actual time=3D1=
0637.681..10637.748 rows=3D286 loops=3D1)
   Sort Key: windspeed.time_group
   ->  Merge Join  (cost=3D153604.82..153614.26 rows=3D322 width=3D48) (act=
ual time=3D10633.375..10636.728 rows=3D286 loops=3D1)
         Merge Cond: ("outer"."?column5?" =3D "inner".doy)
         ->  Sort  (cost=3D594.89..595.33 rows=3D176 width=3D28) (actual ti=
me=3D5.539..5.612 rows=3D286 loops=3D1)
               Sort Key: date_part('doy'::text, unmunge_time(windspeed.time=
_group))
               ->  Bitmap Heap Scan on windspeed  (cost=3D2.62..588.32 rows=
=3D176 width=3D28) (actual time=3D0.918..4.637 rows=3D286 loops=3D1)
                     Recheck Cond: (unmunge_time(time_group) > (now() - '24=
:00:00'::interval))
                     ->  Bitmap Index Scan on minute_windspeed_unmunge_inde=
x  (cost=3D0.00..2.62 rows=3D176 width=3D0) (actual time=3D0.739..0.739 row=
s=3D287 loops=3D1)
                           Index Cond: (unmunge_time(time_group) > (now() -=
 '24:00:00'::interval))
         ->  Sort  (cost=3D153009.93..153010.84 rows=3D366 width=3D20) (act=
ual time=3D10627.699..10627.788 rows=3D295 loops=3D1)
               Sort Key: doy_agg.doy
               ->  HashAggregate  (cost=3D152984.28..152990.69 rows=3D366 w=
idth=3D20) (actual time=3D10625.649..10626.601 rows=3D366 loops=3D1)
                     ->  Seq Scan on readings  (cost=3D0.00..145364.93 rows=
=3D1015914 width=3D20) (actual time=3D0.079..8901.123 rows=3D1015917 loops=
=3D1)
 Total runtime: 10638.298 ms

Where:

weather=3D# \d doy_agg
            View "public.doy_agg"
    Column     |       Type       | Modifiers=20
---------------+------------------+-----------
 doy           | double precision |=20
 avg_windspeed | double precision |=20
 max_windspeed | integer          |=20
View definition:
 SELECT doy_readings.doy, avg(doy_readings.windspeedaverage1) AS avg_windsp=
eed, max(doy_readings.windspeedmax1) AS max_windspeed
   FROM ONLY doy_readings
  GROUP BY doy_readings.doy;

which I don't want because of the full scan on readings.

I can easily do the two queries seperately in the script utilizing this dat=
a, but want to do it in the db itself.  I figure I'm just not seeing how to=
 combine the two queries effectively.

Thoughts?

Thanks,
Rob

--=20
 22:08:50 up 3 days, 14:35,  9 users,  load average: 2.71, 2.48, 2.51
Linux 2.6.12-12-2 #4 SMP Tue Jan 3 19:56:19 MST 2006

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From pgsql-performance-owner@postgresql.org  Wed Jan 11 02:03:58 2006
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Date: Wed, 11 Jan 2006 01:03:48 -0500
To: Mark Lewis <mark.lewis@mir3.com>,pgsql-performance@postgresql.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: help tuning queries on large database
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At 07:28 PM 1/10/2006, Mark Lewis wrote:
>Ron,
>
>A few days back you mentioned:
>
> > Upgrade your kernel to at least  2.6.12
> > There's a known issue with earlier versions of the 2.6.x kernel and
> > 64b CPUs like the Opteron.  See kernel.org for details.
> >
>
>I did some searching and couldn't find any obvious mention of this issue
>(I gave up after searching through the first few hundred instances of
>"64" in the 2.6.12 changelog).
>
>Would you mind being a little more specific about which issue you're
>talking about?  We're about to deploy some new 16GB RAM Opteron DB
>servers and I'd like to check and make sure RH backported whatever the
>fix was to their current RHEL4 kernel.
There are 3 issues I know about in general:
1= As Peter Royal noted on this list, pre 12 versions of 2.6.x have 
problems with RAM of >= 4GB.

2= Pre 12 versions on 2.6.x when running A64 or Xeon 64b SMP seem to 
be susceptible to "context switch storms".

3= Physical and memory IO is considerably improved in the later 
versions of 2.6.x compared to 2.6.11 or earlier.

Talk to a real Linux kernel guru (I am not) for details and specifics.
Ron



From pgsql-performance-owner@postgresql.org  Wed Jan 11 03:57:03 2006
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Date: Wed, 11 Jan 2006 00:56:55 -0700
From: Michael Fuhr <mike@fuhr.org>
To: Robert Creager <Robert_Creager@LogicalChaos.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
Message-ID: <20060111075655.GA51292@winnie.fuhr.org>
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On Tue, Jan 10, 2006 at 10:10:55PM -0700, Robert Creager wrote:
> The query is now correct, but still is slow because of lack of
> index usage.  I don't know how to structure the query correctly to
> use the index.

Have you tried adding restrictions on doy in the WHERE clause?
Something like this, I think:

WHERE ...
  AND doy >= EXTRACT(doy FROM now() - '24 hour'::interval)
  AND doy <= EXTRACT(doy FROM now())

Something else occurred to me: do you (or will you) have more than
one year of data?  If so then matching on doy could be problematic
unless you also check for the year, or unless you want to match
more than one year.

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 04:00:03 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Greg Stark <gsstark@mit.edu>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Tue, Jan 10, 2006 at 10:46:53AM -0500, Tom Lane wrote:
> Not with that data, but maybe if you increased the statistics target for
> the column to 100 or so, you'd catch enough values to get reasonable
> results.

Sorry, I'm not expert with postgresql, could you tell me how to increase
the statistic target?

In another email you said you applied a patch to CVS, please let me know
if you've anything to test for me, and I'll gladly test it immediately
(I've a sandbox so it's ok even if it corrupts the db ;).

Thanks!

From pgsql-performance-owner@postgresql.org  Wed Jan 11 05:00:19 2006
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Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
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On Wed, Jan 11, 2006 at 12:56:55AM -0700, Michael Fuhr wrote:
> WHERE ...
>   AND doy >= EXTRACT(doy FROM now() - '24 hour'::interval)
>   AND doy <= EXTRACT(doy FROM now())

To work on 1 Jan this should be more like

WHERE ...
  AND (doy = EXTRACT(doy FROM now() - '24 hour'::interval) OR
       doy = EXTRACT(doy FROM now()))

In any case the point is to add conditions to the WHERE clause that
will use an index on the table for which you're currently getting
a sequential scan.

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 05:07:49 2006
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Subject: Re: NOT LIKE much faster than LIKE?
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
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On Tue, 2006-01-10 at 22:40 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > I meant use the same sampling approach as I was proposing for ANALYZE,
> > but do this at plan time for the query. That way we can apply the
> > function directly to the sampled rows and estimate selectivity. 
> 
> I think this is so unlikely to be a win as to not even be worth spending
> any time discussing.  The extra planning time across all queries will
> vastly outweigh the occasional improvement in plan choice for some
> queries.

Extra planning time would be bad, so clearly we wouldn't do this when we
already have relevant ANALYZE statistics. 

I would suggest we do this only when all of these are true
- when accessing more than one table, so the selectivity could effect a
join result
- when we have either no ANALYZE statistics, or ANALYZE statistics are
not relevant to estimating selectivity, e.g. LIKE 
- when access against the single table in question cannot find an index
to use from other RestrictInfo predicates

I imagined that this would also be controlled by a GUC, dynamic_sampling
which would be set to zero by default, and give a measure of sample size
to use. (Or just a bool enable_sampling = off (default)).

This is mentioned now because the plan under consideration in this
thread would be improved by this action. It also isn't a huge amount of
code to get it to work.

Best Regards, Simon Riggs


From pgsql-performance-owner@postgresql.org  Wed Jan 11 05:18:44 2006
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Subject: Re: NOT LIKE much faster than LIKE?
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On Wed, Jan 11, 2006 at 09:07:45AM +0000, Simon Riggs wrote:
> I would suggest we do this only when all of these are true
> - when accessing more than one table, so the selectivity could effect a
> join result

FWIW my problem only happens if I join: on the main table where the
kernel_version string is stored (without joins), everything is always
blazing fast. So this requirement certainly sounds fine to me.

From pgsql-performance-owner@postgresql.org  Wed Jan 11 05:42:37 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: 500x speed-down: Wrong statistics!
References: <43C26A5F.7040702@barettadeit.com> <43C27AFA.7060604@beccati.com>
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Tom Lane wrote:
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
> 
>>I have no clue as to how or why the statistics were wrong
>>yesterday--as I vacuum-analyzed continuously out of lack of any better
>>idea--and I was stupid enough to re-timestamp everything before
>>selecting from pg_stats.
> 
> 
> Too bad.  I would be interested to find out how, if the stats were
> up-to-date, the thing was still getting the row estimate so wrong.
> If you manage to get the database back into its prior state please
> do send along the pg_stats info.

I have some more information on this issue, which clears PostgreSQL's planner of 
all suspects. I am observing severe corruption of the bookkeeping fields managed 
by the xdbs rule/trigger "complex". I am unable to pinpoint the cause, right 
now, but the effect is that after running a few hours' test on the end-user 
application (which never interacts directly with xdbs_* fields, and thus cannot 
possibly mangle them) most tuples (the older ones, apparently) get thei 
timestamps set to NULL. Before vacuum-analyzing the table, yesterday's 
statistics were in effect, and the planner used the appropriate indexes. Now, 
after vacuum-analyzing the table, the pg_stats row for the xdbs_modified field 
no longer exists (!), and the planner has reverted to the Nested Loop Seq Scan 
join strategy. Hence, all the vacuum-analyzing I was doing when complaining 
against the planner was actually collecting completely screwed statistics, and 
this is why the ALTER TABLE ... SET STATISTICS 1000 did not help at all!

Ok. I plead guilty and ask for the clemency of the court. I'll pay my debt with 
society with a long term of pl/pgsql code debugging...

Alex

From pgsql-performance-owner@postgresql.org  Wed Jan 11 06:59:55 2006
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To: pgsql-performance@postgresql.org
From: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
Subject: Slow query with joins
Date: Wed, 11 Jan 2006 11:59:39 +0100
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Hello!
Has anyone got any tips for speeding up this query? It currently  
takes hours to start.

PostgreSQL v8.x on (SuSe Linux)
Thanks!


no_people=# explain SELECT r.id AS r_id, r.firstname || ' ' ||  
r.lastname AS r_name, ad.id AS ad_id, ad.type AS ad_type, ad.address  
AS ad_address, ad.postalcode AS ad_postalcode, ad.postalsite AS  
ad_postalsite, ad.priority AS ad_priority, ad.position[0] AS ad_lat,  
ad.position[1] AS ad_lon, ad.uncertainty AS ad_uncertainty, ad.extra  
AS ad_extra, co.id AS co_id, co.type AS co_type, co.value AS  
co_value, co.description AS co_description, co.priority AS  
co_priority, co.visible AS co_visible, co.searchable AS co_searchable

FROM people r
LEFT OUTER JOIN addresses ad ON(r.id = ad.record)
LEFT OUTER JOIN contacts co ON(r.id = co.record)
WHERE r.deleted = false AND  r.original IS NULL AND co.deleted =  
false AND NOT ad.deleted
ORDER BY r.id;

                                                           QUERY PLAN
------------------------------------------------------------------------ 
-------------------------------------------------------
Sort  (cost=1152540.74..1152988.20 rows=178983 width=585)
    Sort Key: r.id
    ->  Hash Join  (cost=313757.11..1005334.96 rows=178983 width=585)
          Hash Cond: ("outer".record = "inner".id)
          ->  Seq Scan on addresses ad  (cost=0.00..428541.29  
rows=4952580 width=136)
                Filter: (NOT deleted)
          ->  Hash  (cost=312039.95..312039.95 rows=27664 width=457)
                ->  Hash Join  (cost=94815.24..312039.95 rows=27664  
width=457)
                      Hash Cond: ("outer".record = "inner".id)
                      ->  Seq Scan on contacts co   
(cost=0.00..147791.54 rows=5532523 width=430)
                            Filter: (deleted = false)
                      ->  Hash  (cost=94755.85..94755.85 rows=23755  
width=27)
                            ->  Index Scan using  
people_original_is_null on people r  (cost=0.00..94755.85 rows=23755  
width=27)
                                  Filter: ((deleted = false) AND  
(original IS NULL))
(14 rows)






no_people=# \d contacts
                                      Table "public.contacts"
    Column    |          Type          |                         
Modifiers
-------------+------------------------ 
+----------------------------------------------------------
id          | integer                | not null default nextval 
('public.contacts_id_seq'::text)
record      | integer                |
type        | integer                |
value       | character varying(128) |
description | character varying(255) |
priority    | integer                |
itescotype  | integer                |
original    | integer                |
source      | integer                |
reference   | character varying(32)  |
deleted     | boolean                | not null default false
quality     | integer                |
visible     | boolean                | not null default true
searchable  | boolean                | not null default true
Indexes:
     "contacts_pkey" PRIMARY KEY, btree (id)
     "contacts_deleted_idx" btree (deleted)
     "contacts_record_idx" btree (record) CLUSTER
     "contacts_source_reference_idx" btree (source, reference)









no_people=# \d addresses
                                      Table "public.addresses"
    Column    |          Type          |                          
Modifiers
-------------+------------------------ 
+-----------------------------------------------------------
id          | integer                | not null default nextval 
('public.addresses_id_seq'::text)
record      | integer                |
address     | character varying(128) |
extra       | character varying(32)  |
postalcode  | character varying(16)  |
postalsite  | character varying(64)  |
description | character varying(255) |
position    | point                  |
uncertainty | integer                | default 99999999
priority    | integer                |
type        | integer                |
place       | character varying(64)  |
floor       | integer                |
side        | character varying(8)   |
housename   | character varying(64)  |
original    | integer                |
source      | integer                |
reference   | character varying(32)  |
deleted     | boolean                | not null default false
quality     | integer                |
visible     | boolean                | not null default true
searchable  | boolean                | not null default true
Indexes:
     "addresses_pkey" PRIMARY KEY, btree (id)
     "addresses_deleted_idx" btree (deleted)
     "addresses_record_idx" btree (record) CLUSTER
     "addresses_source_reference_idx" btree (source, reference)








no_people=# \d people
                                      Table "public.people"
    Column   |           Type           |                        
Modifiers
------------+-------------------------- 
+--------------------------------------------------------
id         | integer                  | not null default nextval 
('public.people_id_seq'::text)
origid     | integer                  |
firstname  | character varying(128)   | default ''::character varying
middlename | character varying(128)   | default ''::character varying
lastname   | character varying(128)   | default ''::character varying
updated    | timestamp with time zone | default  
('now'::text)::timestamp(6) with time zone
updater    | integer                  |
relevance  | real                     | not null default 0
phonetic   | text                     |
indexed    | boolean                  | default false
record     | text                     |
original   | integer                  |
active     | boolean                  | default true
title      | character varying(128)   |
deleted    | boolean                  | not null default false
Indexes:
     "people_pkey" PRIMARY KEY, btree (id)
     "people_indexed_idx" btree (indexed)
     "people_lower_lastname_firstname_idx" btree (lower 
(lastname::text), lower(firstname::text))
     "people_original_is_null" btree (original) WHERE original IS NULL
     "people_relevance_idx" btree (relevance)
     "person_updated_idx" btree (updated)

no_people=# 

From pgsql-performance-owner@postgresql.org  Wed Jan 11 10:27:04 2006
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Date: Wed, 11 Jan 2006 07:26:59 -0700
From: Robert Creager <Robert_Creager@LogicalChaos.org>
To: Michael Fuhr <mike@fuhr.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
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When grilled further on (Wed, 11 Jan 2006 00:56:55 -0700),
Michael Fuhr <mike@fuhr.org> confessed:

> On Tue, Jan 10, 2006 at 10:10:55PM -0700, Robert Creager wrote:
> > The query is now correct, but still is slow because of lack of
> > index usage.  I don't know how to structure the query correctly to
> > use the index.
>=20
> Have you tried adding restrictions on doy in the WHERE clause?
> Something like this, I think:

I cannot.  That's what I thought I would get from the join.  The query show=
n will always have two days involved, and only grows from there.  The data =
is graphed at http://www.logicalchaos.org/weather/index.html, and I'm looki=
ng at adding historical data to the graphs.

Opps, never mind.  You hit the nail on the head:

weather-# SELECT *, unmunge_time( time_group ) AS time,
weather-# EXTRACT( doy FROM unmunge_time( time_group ) )
weather-# FROM minute."windspeed"
weather-# JOIN doy_agg ON( EXTRACT( doy FROM unmunge_time( time_group ) ) =
=3D doy )
weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interval =
)=20
weather-# AND doy BETWEEN EXTRACT( doy FROM now() - '24 hour'::interval)=20
weather-#             AND EXTRACT( doy FROM now() )
weather-# ORDER BY time_group;
                                                                           =
                        QUERY PLAN                                         =
                                                         =20
---------------------------------------------------------------------------=
---------------------------------------------------------------------------=
----------------------------------------------------------
 Sort  (cost=3D21914.09..21914.10 rows=3D1 width=3D48) (actual time=3D76.59=
5..76.662 rows=3D286 loops=3D1)
   Sort Key: windspeed.time_group
   ->  Hash Join  (cost=3D21648.19..21914.08 rows=3D1 width=3D48) (actual t=
ime=3D64.656..75.562 rows=3D286 loops=3D1)
         Hash Cond: (date_part('doy'::text, unmunge_time("outer".time_group=
)) =3D "inner".doy)
         ->  Bitmap Heap Scan on windspeed  (cost=3D2.27..267.40 rows=3D74 =
width=3D28) (actual time=3D0.585..1.111 rows=3D286 loops=3D1)
               Recheck Cond: (unmunge_time(time_group) > (now() - '24:00:00=
'::interval))
               ->  Bitmap Index Scan on minute_windspeed_unmunge_index  (co=
st=3D0.00..2.27 rows=3D74 width=3D0) (actual time=3D0.566..0.566 rows=3D287=
 loops=3D1)
                     Index Cond: (unmunge_time(time_group) > (now() - '24:0=
0:00'::interval))
         ->  Hash  (cost=3D21645.92..21645.92 rows=3D3 width=3D20) (actual =
time=3D63.849..63.849 rows=3D2 loops=3D1)
               ->  HashAggregate  (cost=3D21645.84..21645.89 rows=3D3 width=
=3D20) (actual time=3D63.832..63.834 rows=3D2 loops=3D1)
                     ->  Bitmap Heap Scan on readings  (cost=3D59.21..21596=
.85 rows=3D6532 width=3D20) (actual time=3D15.174..53.249 rows=3D7613 loops=
=3D1)
                           Recheck Cond: ((date_part('doy'::text, "when") >=
=3D date_part('doy'::text, (now() - '24:00:00'::interval))) AND (date_part(=
'doy'::text, "when") <=3D date_part('doy'::text, now())))
                           ->  Bitmap Index Scan on readings_doy_index  (co=
st=3D0.00..59.21 rows=3D6532 width=3D0) (actual time=3D12.509..12.509 rows=
=3D10530 loops=3D1)
                                 Index Cond: ((date_part('doy'::text, "when=
") >=3D date_part('doy'::text, (now() - '24:00:00'::interval))) AND (date_p=
art('doy'::text, "when") <=3D date_part('doy'::text, now())))
 Total runtime: 77.177 ms

What I had thought is that PG would (could?) be smart enough to realize tha=
t one query was restricted, and apply that restriction to the other based o=
n the join.  I know it works in other cases (using indexes on both tables u=
sing the join)...

>=20
> Something else occurred to me: do you (or will you) have more than
> one year of data?  If so then matching on doy could be problematic
> unless you also check for the year, or unless you want to match
> more than one year.

Yes and yes.  I'm doing both aggregate by day of the year for all data, and=
 aggregate by day of year within each year.  The examples are:

weather=3D# select * from doy_agg where doy =3D extract( doy from now() );
 doy |  avg_windspeed   | max_windspeed=20
-----+------------------+---------------
  11 | 6.14058239764748 |            69
(1 row)

weather=3D# select * from doy_day_agg where extract( doy from day ) =3D ext=
ract( doy from now() );
         day         |  avg_windspeed   | max_windspeed=20
---------------------+------------------+---------------
 2004-01-11 00:00:00 | 5.03991313397539 |            17
 2006-01-11 00:00:00 |  18.532050716667 |            69
 2005-01-11 00:00:00 |  3.6106763448041 |            13

Thanks for your help Michael.

Cheers,
Rob

--=20
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Linux 2.6.12-12-2 #4 SMP Tue Jan 3 19:56:19 MST 2006

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Subject: Re: Index isn't used during a join.
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When grilled further on (Wed, 11 Jan 2006 07:26:59 -0700),
Robert Creager <Robert_Creager@LogicalChaos.org> confessed:

>=20
> weather-# SELECT *, unmunge_time( time_group ) AS time,
> weather-# EXTRACT( doy FROM unmunge_time( time_group ) )
> weather-# FROM minute."windspeed"
> weather-# JOIN doy_agg ON( EXTRACT( doy FROM unmunge_time( time_group ) )=
 =3D doy )
> weather-# WHERE unmunge_time( time_group ) > ( now() - '24 hour'::interva=
l )=20
> weather-# AND doy BETWEEN EXTRACT( doy FROM now() - '24 hour'::interval)=
=20
> weather-#             AND EXTRACT( doy FROM now() )
> weather-# ORDER BY time_group;

The more I think about it, the more I believe PG is missing an opportunity.=
  The query is adequately constrained without the BETWEEN clause.  Why does=
n't PG see that?  I realize I'm a hack and by db organization shows that...

The query is wrong as stated, as it won't work when the interval crosses a =
year boundary, but it's a stop gap for now.

Cheers,
Rob

--=20
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Date: Wed, 11 Jan 2006 10:03:36 -0500
From: Pallav Kalva <pkalva@livedatagroup.com>
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Subject: Postgres8.0 Planner chooses WRONG plan.
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Hi ,


    I am having problem optimizing this query, Postgres optimizer uses a 
plan which invloves seq-scan on a table. And when I choose a option to 
disable seq-scan it uses index-scan and obviously the query is much faster.
    All tables are daily vacummed and analyzed as per docs.

   Why cant postgres use index-scan ?


Postgres Version:8.0.2
Platform : Fedora

Here is the explain analyze output. Let me know if any more information 
is needed.  Can we make postgres use index scan for this query ?

Thanks!
Pallav.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
explain analyze
 select * from provisioning.alerts where countystate = 'FL' and countyno 
= '099' and status = 'ACTIVE' ;

                                                                    
QUERY PLAN                                                               
--------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=3.45..15842.17 rows=1 width=125) (actual 
time=913.491..18992.009 rows=110 loops=1)
   ->  Nested Loop  (cost=3.45..15838.88 rows=1 width=86) (actual 
time=913.127..18958.482 rows=110 loops=1)
         ->  Hash Join  (cost=3.45..15835.05 rows=1 width=82) (actual 
time=913.093..18954.951 rows=110 loops=1)
               Hash Cond: ("outer".fkserviceinstancestatusid = 
"inner".serviceinstancestatusid)
               ->  Hash Join  (cost=2.38..15833.96 rows=2 width=74) 
(actual time=175.139..18952.830 rows=358 loops=1)
                     Hash Cond: ("outer".fkserviceofferingid = 
"inner".serviceofferingid)
                     ->  Seq Scan on serviceinstance si  
(cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
rows=358 loops=1)
                           Filter: (((subplan) = 'FL'::text) AND 
((subplan) = '099'::text))
                           SubPlan
                             ->  Result  (cost=0.00..0.01 rows=1 
width=0) (actual time=0.090..0.093 rows=1 loops=3923)
                             ->  Result  (cost=0.00..0.01 rows=1 
width=0) (actual time=0.058..0.061 rows=1 loops=265617)
                     ->  Hash  (cost=2.38..2.38 rows=3 width=4) (actual 
time=0.444..0.444 rows=0 loops=1)
                           ->  Hash Join  (cost=1.08..2.38 rows=3 
width=4) (actual time=0.312..0.428 rows=1 loops=1)
                                 Hash Cond: ("outer".fkserviceid = 
"inner".serviceid)
                                 ->  Seq Scan on serviceoffering so  
(cost=0.00..1.18 rows=18 width=8) (actual time=0.005..0.068 rows=18 loops=1)
                                 ->  Hash  (cost=1.07..1.07 rows=1 
width=4) (actual time=0.036..0.036 rows=0 loops=1)
                                       ->  Seq Scan on service s  
(cost=0.00..1.07 rows=1 width=4) (actual time=0.014..0.019 rows=1 loops=1)
                                             Filter: (servicename = 
'alert'::text)
               ->  Hash  (cost=1.06..1.06 rows=1 width=16) (actual 
time=0.044..0.044 rows=0 loops=1)
                     ->  Seq Scan on serviceinstancestatus sis  
(cost=0.00..1.06 rows=1 width=16) (actual time=0.017..0.024 rows=1 loops=1)
                           Filter: (status = 'ACTIVE'::text)
         ->  Index Scan using pk_account_accountid on account a  
(cost=0.00..3.82 rows=1 width=8) (actual time=0.012..0.016 rows=1 loops=110)
               Index Cond: ("outer".fkaccountid = a.accountid)
   ->  Index Scan using pk_contact_contactid on contact c  
(cost=0.00..3.24 rows=1 width=47) (actual time=0.014..0.018 rows=1 
loops=110)
         Index Cond: ("outer".fkcontactid = c.contactid)
   SubPlan
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.072..0.075 rows=1 loops=110)
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.079..0.082 rows=1 loops=110)
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.086..0.089 rows=1 loops=110)
 Total runtime: 18992.694 ms
(30 rows)

Time: 18996.203 ms

--> As you can see the ->  Seq Scan on serviceinstance si  
(cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
rows=358 loops=1) was taking too long .
    same query when i disable the seq-scan it uses index-scan and its 
much faster now

set enable_seqscan=false;
SET
Time: 0.508 ms
explain analyze
select * from provisioning.alerts where countystate = 'FL' and countyno 
= '099' and status = 'ACTIVE' ;

                                                                                             
QUERY PLAN                                      
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=9.10..16676.10 rows=1 width=125) (actual 
time=24.792..3898.939 rows=110 loops=1)
   ->  Nested Loop  (cost=9.10..16672.81 rows=1 width=86) (actual 
time=24.383..3862.025 rows=110 loops=1)
         ->  Hash Join  (cost=9.10..16668.97 rows=1 width=82) (actual 
time=24.351..3858.351 rows=110 loops=1)
               Hash Cond: ("outer".fkserviceofferingid = 
"inner".serviceofferingid)
               ->  Nested Loop  (cost=0.00..16659.85 rows=2 width=86) 
(actual time=8.449..3841.260 rows=110 loops=1)
                     ->  Index Scan using 
pk_serviceinstancestatus_serviceinstancestatusid on 
serviceinstancestatus sis  (cost=0.00..3.07 rows=1 width=16) (actual 
time=3.673..3.684 rows=1 loops=1)
                           Filter: (status = 'ACTIVE'::text)
                     ->  Index Scan using 
idx_serviceinstance_fkserviceinstancestatusid on serviceinstance si  
(cost=0.00..16656.76 rows=2 width=78) (actual time=4.755..3836.399 
rows=110 loops=1)
                           Index Cond: (si.fkserviceinstancestatusid = 
"outer".serviceinstancestatusid)
                           Filter: (((subplan) = 'FL'::text) AND 
((subplan) = '099'::text))
                           SubPlan
                             ->  Result  (cost=0.00..0.01 rows=1 
width=0) (actual time=0.125..0.128 rows=1 loops=1283)
                             ->  Result  (cost=0.00..0.01 rows=1 
width=0) (actual time=0.083..0.086 rows=1 loops=26146)
               ->  Hash  (cost=9.09..9.09 rows=3 width=4) (actual 
time=15.661..15.661 rows=0 loops=1)
                     ->  Nested Loop  (cost=0.00..9.09 rows=3 width=4) 
(actual time=15.617..15.637 rows=1 loops=1)
                           ->  Index Scan using uk_service_servicename 
on service s  (cost=0.00..3.96 rows=1 width=4) (actual 
time=11.231..11.236 rows=1 loops=1)
                                 Index Cond: (servicename = 'alert'::text)
                           ->  Index Scan using 
idx_serviceoffering_fkserviceid on serviceoffering so  (cost=0.00..5.09 
rows=3 width=8) (actual time=4.366..4.371 rows=1 loops=1)
                                 Index Cond: ("outer".serviceid = 
so.fkserviceid)
         ->  Index Scan using pk_account_accountid on account a  
(cost=0.00..3.82 rows=1 width=8) (actual time=0.013..0.017 rows=1 loops=110)
               Index Cond: ("outer".fkaccountid = a.accountid)
   ->  Index Scan using pk_contact_contactid on contact c  
(cost=0.00..3.24 rows=1 width=47) (actual time=0.013..0.017 rows=1 
loops=110)
         Index Cond: ("outer".fkcontactid = c.contactid)
   SubPlan
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.081..0.084 rows=1 loops=110)
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.088..0.091 rows=1 loops=110)
     ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.098..0.101 rows=1 loops=110)
 Total runtime: 3899.589 ms
(28 rows)


Here is the view definition
-------------------------------

       View "provisioning.alerts"
      Column       |  Type   | Modifiers
-------------------+---------+-----------
 serviceinstanceid | integer |
 accountid         | integer |
 firstname         | text    |
 lastname          | text    |
 email             | text    |
 status            | text    |
 affiliate         | text    |
 affiliatesub      | text    |
 domain            | text    |
 countyno          | text    |
 countystate       | text    |
 listingtype       | text    |
View definition:
 SELECT si.serviceinstanceid, a.accountid, c.firstname, c.lastname, 
c.email, sis.status, si.affiliate, si.affiliatesub, si."domain",
               ( SELECT get_parametervalue(si.serviceinstanceid, 
'countyNo'::text) AS get_parametervalue) AS countyno,
              ( SELECT get_parametervalue(si.serviceinstanceid, 
'countyState'::text) AS get_parametervalue) AS countystate,
              ( SELECT get_parametervalue(si.serviceinstanceid, 
'listingType'::text) AS get_parametervalue) AS listingtype
   FROM provisioning.account a, common.contact c, provisioning.service 
s, provisioning.serviceoffering so, provisioning.serviceinstance si, 
provisioning.serviceinstancestatus sis
  WHERE si.fkserviceofferingid = so.serviceofferingid
  AND si.fkserviceinstancestatusid = sis.serviceinstancestatusid
 AND s.serviceid = so.fkserviceid
 AND a.fkcontactid = c.contactid
 AND si.fkaccountid = a.accountid
AND s.servicename = 'alert'::text;

Function Definition
----------------------

CREATE OR REPLACE FUNCTION get_parametervalue(v_fkserviceinstanceid 
integer, v_name text) RETURNS TEXT AS $$
DECLARE
        v_value        text;
BEGIN
        SELECT  p.value
        INTO    v_value
        FROM    provisioning.serviceinstanceparameter sip, 
common.parameter p
        WHERE   fkserviceinstanceid = v_fkserviceinstanceid
        AND     sip.fkparameterid = p.parameterid
        AND     p.name = v_name;

        RETURN  v_value;

END

Serviceinstance table stats
-----------------------------

select relname, relpages, reltuples from pg_class where relname = 
'serviceinstance';
     relname     | relpages | reltuples
-----------------+----------+-----------
 serviceinstance |     5207 |    265613

$$ language plpgsql





From pgsql-performance-owner@postgresql.org  Wed Jan 11 11:27:38 2006
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Date: Wed, 11 Jan 2006 10:27:39 -0500
From: Pallav Kalva <pkalva@livedatagroup.com>
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To: PGPerformance <pgsql-performance@postgresql.org>
Subject: Postgres8.0 planner chooses WRONG plan
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X-Sequence-Number: 16590

Hi ,


   I am having problem optimizing this query, Postgres optimizer uses a 
plan which invloves seq-scan on a table. And when I choose a option to 
disable seq-scan it uses index-scan and obviously the query is much faster.
   All tables are daily vacummed and analyzed as per docs.

  Why cant postgres use index-scan ?


Postgres Version:8.0.2
Platform : Fedora

Here is the explain analyze output. Let me know if any more information 
is needed.  Can we make postgres use index scan for this query ?

Thanks!
Pallav.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 

explain analyze
select * from provisioning.alerts where countystate = 'FL' and countyno 
= '099' and status = 'ACTIVE' ;

                                                                   QUERY 
PLAN                                                               
-------------------------------------------------------------------------------------------------------------------------------------------------- 

Nested Loop  (cost=3.45..15842.17 rows=1 width=125) (actual 
time=913.491..18992.009 rows=110 loops=1)
  ->  Nested Loop  (cost=3.45..15838.88 rows=1 width=86) (actual 
time=913.127..18958.482 rows=110 loops=1)
        ->  Hash Join  (cost=3.45..15835.05 rows=1 width=82) (actual 
time=913.093..18954.951 rows=110 loops=1)
              Hash Cond: ("outer".fkserviceinstancestatusid = 
"inner".serviceinstancestatusid)
              ->  Hash Join  (cost=2.38..15833.96 rows=2 width=74) 
(actual time=175.139..18952.830 rows=358 loops=1)
                    Hash Cond: ("outer".fkserviceofferingid = 
"inner".serviceofferingid)
                    ->  Seq Scan on serviceinstance si  
(cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
rows=358 loops=1)
                          Filter: (((subplan) = 'FL'::text) AND 
((subplan) = '099'::text))
                          SubPlan
                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
(actual time=0.090..0.093 rows=1 loops=3923)
                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
(actual time=0.058..0.061 rows=1 loops=265617)
                    ->  Hash  (cost=2.38..2.38 rows=3 width=4) (actual 
time=0.444..0.444 rows=0 loops=1)
                          ->  Hash Join  (cost=1.08..2.38 rows=3 
width=4) (actual time=0.312..0.428 rows=1 loops=1)
                                Hash Cond: ("outer".fkserviceid = 
"inner".serviceid)
                                ->  Seq Scan on serviceoffering so  
(cost=0.00..1.18 rows=18 width=8) (actual time=0.005..0.068 rows=18 
loops=1)
                                ->  Hash  (cost=1.07..1.07 rows=1 
width=4) (actual time=0.036..0.036 rows=0 loops=1)
                                      ->  Seq Scan on service s  
(cost=0.00..1.07 rows=1 width=4) (actual time=0.014..0.019 rows=1 loops=1)
                                            Filter: (servicename = 
'alert'::text)
              ->  Hash  (cost=1.06..1.06 rows=1 width=16) (actual 
time=0.044..0.044 rows=0 loops=1)
                    ->  Seq Scan on serviceinstancestatus sis  
(cost=0.00..1.06 rows=1 width=16) (actual time=0.017..0.024 rows=1 loops=1)
                          Filter: (status = 'ACTIVE'::text)
        ->  Index Scan using pk_account_accountid on account a  
(cost=0.00..3.82 rows=1 width=8) (actual time=0.012..0.016 rows=1 
loops=110)
              Index Cond: ("outer".fkaccountid = a.accountid)
  ->  Index Scan using pk_contact_contactid on contact c  
(cost=0.00..3.24 rows=1 width=47) (actual time=0.014..0.018 rows=1 
loops=110)
        Index Cond: ("outer".fkcontactid = c.contactid)
  SubPlan
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.072..0.075 rows=1 loops=110)
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.079..0.082 rows=1 loops=110)
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.086..0.089 rows=1 loops=110)
Total runtime: 18992.694 ms
(30 rows)

Time: 18996.203 ms

--> As you can see the ->  Seq Scan on serviceinstance si  
(cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
rows=358 loops=1) was taking too long .
   same query when i disable the seq-scan it uses index-scan and its 
much faster now

set enable_seqscan=false;
SET
Time: 0.508 ms
explain analyze
select * from provisioning.alerts where countystate = 'FL' and countyno 
= '099' and status = 'ACTIVE' ;

                                                                                            
QUERY PLAN                                      
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 

Nested Loop  (cost=9.10..16676.10 rows=1 width=125) (actual 
time=24.792..3898.939 rows=110 loops=1)
  ->  Nested Loop  (cost=9.10..16672.81 rows=1 width=86) (actual 
time=24.383..3862.025 rows=110 loops=1)
        ->  Hash Join  (cost=9.10..16668.97 rows=1 width=82) (actual 
time=24.351..3858.351 rows=110 loops=1)
              Hash Cond: ("outer".fkserviceofferingid = 
"inner".serviceofferingid)
              ->  Nested Loop  (cost=0.00..16659.85 rows=2 width=86) 
(actual time=8.449..3841.260 rows=110 loops=1)
                    ->  Index Scan using 
pk_serviceinstancestatus_serviceinstancestatusid on 
serviceinstancestatus sis  (cost=0.00..3.07 rows=1 width=16) (actual 
time=3.673..3.684 rows=1 loops=1)
                          Filter: (status = 'ACTIVE'::text)
                    ->  Index Scan using 
idx_serviceinstance_fkserviceinstancestatusid on serviceinstance si  
(cost=0.00..16656.76 rows=2 width=78) (actual time=4.755..3836.399 
rows=110 loops=1)
                          Index Cond: (si.fkserviceinstancestatusid = 
"outer".serviceinstancestatusid)
                          Filter: (((subplan) = 'FL'::text) AND 
((subplan) = '099'::text))
                          SubPlan
                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
(actual time=0.125..0.128 rows=1 loops=1283)
                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
(actual time=0.083..0.086 rows=1 loops=26146)
              ->  Hash  (cost=9.09..9.09 rows=3 width=4) (actual 
time=15.661..15.661 rows=0 loops=1)
                    ->  Nested Loop  (cost=0.00..9.09 rows=3 width=4) 
(actual time=15.617..15.637 rows=1 loops=1)
                          ->  Index Scan using uk_service_servicename on 
service s  (cost=0.00..3.96 rows=1 width=4) (actual time=11.231..11.236 
rows=1 loops=1)
                                Index Cond: (servicename = 'alert'::text)
                          ->  Index Scan using 
idx_serviceoffering_fkserviceid on serviceoffering so  (cost=0.00..5.09 
rows=3 width=8) (actual time=4.366..4.371 rows=1 loops=1)
                                Index Cond: ("outer".serviceid = 
so.fkserviceid)
        ->  Index Scan using pk_account_accountid on account a  
(cost=0.00..3.82 rows=1 width=8) (actual time=0.013..0.017 rows=1 
loops=110)
              Index Cond: ("outer".fkaccountid = a.accountid)
  ->  Index Scan using pk_contact_contactid on contact c  
(cost=0.00..3.24 rows=1 width=47) (actual time=0.013..0.017 rows=1 
loops=110)
        Index Cond: ("outer".fkcontactid = c.contactid)
  SubPlan
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.081..0.084 rows=1 loops=110)
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.088..0.091 rows=1 loops=110)
    ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual 
time=0.098..0.101 rows=1 loops=110)
Total runtime: 3899.589 ms
(28 rows)


Here is the view definition
-------------------------------

      View "provisioning.alerts"
     Column       |  Type   | Modifiers
-------------------+---------+-----------
serviceinstanceid | integer |
accountid         | integer |
firstname         | text    |
lastname          | text    |
email             | text    |
status            | text    |
affiliate         | text    |
affiliatesub      | text    |
domain            | text    |
countyno          | text    |
countystate       | text    |
listingtype       | text    |
View definition:
SELECT si.serviceinstanceid, a.accountid, c.firstname, c.lastname, 
c.email, sis.status, si.affiliate, si.affiliatesub, si."domain",
              ( SELECT get_parametervalue(si.serviceinstanceid, 
'countyNo'::text) AS get_parametervalue) AS countyno,
             ( SELECT get_parametervalue(si.serviceinstanceid, 
'countyState'::text) AS get_parametervalue) AS countystate,
             ( SELECT get_parametervalue(si.serviceinstanceid, 
'listingType'::text) AS get_parametervalue) AS listingtype
  FROM provisioning.account a, common.contact c, provisioning.service s, 
provisioning.serviceoffering so, provisioning.serviceinstance si, 
provisioning.serviceinstancestatus sis
 WHERE si.fkserviceofferingid = so.serviceofferingid
 AND si.fkserviceinstancestatusid = sis.serviceinstancestatusid
AND s.serviceid = so.fkserviceid
AND a.fkcontactid = c.contactid
AND si.fkaccountid = a.accountid
AND s.servicename = 'alert'::text;

Function Definition
----------------------

CREATE OR REPLACE FUNCTION get_parametervalue(v_fkserviceinstanceid 
integer, v_name text) RETURNS TEXT AS $$
DECLARE
       v_value        text;
BEGIN
       SELECT  p.value
       INTO    v_value
       FROM    provisioning.serviceinstanceparameter sip, 
common.parameter p
       WHERE   fkserviceinstanceid = v_fkserviceinstanceid
       AND     sip.fkparameterid = p.parameterid
       AND     p.name = v_name;

       RETURN  v_value;

END

Serviceinstance table stats
-----------------------------

select relname, relpages, reltuples from pg_class where relname = 
'serviceinstance';
    relname     | relpages | reltuples
-----------------+----------+-----------
serviceinstance |     5207 |    265613

$$ language plpgsql





From pgsql-performance-owner@postgresql.org  Wed Jan 11 11:33:08 2006
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To: Robert Creager <Robert_Creager@LogicalChaos.org>
cc: Michael Fuhr <mike@fuhr.org>,
	PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join. 
In-reply-to: <20060111072659.7c1772ad@thunder.logicalchaos.org> 
References: <20060109212338.6420af12@thunder.logicalchaos.org>
	<20060110055818.GA55076@winnie.fuhr.org>
	<20060110221055.053596ab@thunder.logicalchaos.org>
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	<20060111072659.7c1772ad@thunder.logicalchaos.org>
Comments: In-reply-to Robert Creager <Robert_Creager@LogicalChaos.org>
	message dated "Wed, 11 Jan 2006 07:26:59 -0700"
Date: Wed, 11 Jan 2006 10:33:03 -0500
Message-ID: <12877.1136993583@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Robert Creager <Robert_Creager@LogicalChaos.org> writes:
> What I had thought is that PG would (could?) be smart enough to realize tha=
> t one query was restricted, and apply that restriction to the other based o=
> n the join.  I know it works in other cases (using indexes on both tables u=
> sing the join)...

The planner understands about transitivity of equality, ie given a = b
and b = c it can infer a = c.  It doesn't do any such thing for
inequalities though, nor does it deduce f(a) = f(b) for arbitrary
functions f.  The addition Michael suggested requires much more
understanding of the properties of the functions in your query than
I think would be reasonable to put into the planner.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 11:45:48 2006
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To: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow query with joins 
In-reply-to: <C24D65E0-2D32-43DF-ABCD-79A47C5243AF@gmail.com> 
References: <C24D65E0-2D32-43DF-ABCD-79A47C5243AF@gmail.com>
Comments: In-reply-to Bendik Rognlien Johansen <bendik.johansen@gmail.com>
	message dated "Wed, 11 Jan 2006 11:59:39 +0100"
Date: Wed, 11 Jan 2006 10:45:47 -0500
Message-ID: <13028.1136994347@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bendik Rognlien Johansen <bendik.johansen@gmail.com> writes:
> Has anyone got any tips for speeding up this query? It currently  
> takes hours to start.

Are the rowcount estimates close to reality?  The plan doesn't look
unreasonable to me if they are.  It might help to increase work_mem
to ensure that the hash tables don't spill to disk.

Indexes:
     "people_original_is_null" btree (original) WHERE original IS NULL

This index seems poorly designed: the actual index entries are dead
weight since all of them are necessarily NULL.  You might as well make
the index carry something that you frequently test in conjunction with
"original IS NULL".  For instance, if this particular query is a common
case, you could replace this index with

CREATE INDEX people_deleted_original_is_null ON people(deleted)
  WHERE original IS NULL;

This index is still perfectly usable for queries that only say "original
IS NULL", but it can also filter out rows with the wrong value of
deleted.  Now, if there are hardly any rows with deleted = true, maybe
this won't help much for your problem.  But in any case you ought to
consider whether you can make the index entries do something useful.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 12:07:29 2006
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To: Pallav Kalva <pkalva@livedatagroup.com>
cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Postgres8.0 planner chooses WRONG plan 
In-reply-to: <43C523EB.3000201@livedatagroup.com> 
References: <43C523EB.3000201@livedatagroup.com>
Comments: In-reply-to Pallav Kalva <pkalva@livedatagroup.com>
	message dated "Wed, 11 Jan 2006 10:27:39 -0500"
Date: Wed, 11 Jan 2006 11:07:18 -0500
Message-ID: <13187.1136995638@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Pallav Kalva <pkalva@livedatagroup.com> writes:
>    I am having problem optimizing this query,

Get rid of the un-optimizable function inside the view.  You've
converted something that should be a join into an unreasonably large
number of function calls.

>                     ->  Seq Scan on serviceinstance si  
> (cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
> rows=358 loops=1)
>                           Filter: (((subplan) = 'FL'::text) AND 
> ((subplan) = '099'::text))
>                           SubPlan
>                             ->  Result  (cost=0.00..0.01 rows=1 width=0) 
> (actual time=0.090..0.093 rows=1 loops=3923)
>                             ->  Result  (cost=0.00..0.01 rows=1 width=0) 
> (actual time=0.058..0.061 rows=1 loops=265617)

The bulk of the cost here is in the second subplan (0.061 * 265617 =
16202.637 msec total runtime), and there's not a darn thing Postgres
can do to improve this because the work is all down inside a "black box"
function.  In fact the planner does not even know that the function call
is expensive, else it would have preferred a plan that requires fewer
evaluations of the function.  The alternative plan you show is *not*
faster "because it's an indexscan"; it's faster because get_parametervalue
is evaluated fewer times.

The useless sub-SELECTs atop the function calls are adding their own
little increment of wasted time, too.  I'm not sure how bad that is
relative to the function calls, but it's certainly not helping.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 12:45:07 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
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Subject: Re: Postgres8.0 planner chooses WRONG plan
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Hi Tom,

     Thanks! for your input, the view was written first without using 
the function but its an ugly big with all the joins and its much slower 
that way. Below is the view without the function and its explain analzye 
output , as you can see the it takes almost 2 min to run this query with 
this view . Is there any way to optimize or make changes to this view ?

Thanks!
Pallav.


View Definition
-------------------

create or replace view provisioning.alertserviceinstanceold as
SELECT services.serviceinstanceid, a.accountid, c.firstname, c.lastname, 
c.email, services.countyno, services.countystate, services.listingtype 
AS listingtypename, services.status, services.affiliate, 
services.affiliatesub, services."domain"
   FROM provisioning.account a
   JOIN common.contact c ON a.fkcontactid = c.contactid
   JOIN ( SELECT p1.serviceinstanceid, p1.accountid, p1.countyno, 
p2.countystate, p3.listingtype, p1.status, p1.affiliate, 
p1.affiliatesub, p1."domain"
      FROM ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
si."domain", si.fkaccountid AS accountid, p.value AS countyno, sis.status
              FROM provisioning.service s
         JOIN provisioning.serviceoffering so ON s.serviceid = 
so.fkserviceid
    JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
si.fkserviceofferingid
   JOIN provisioning.serviceinstancestatus sis ON 
si.fkserviceinstancestatusid = sis.serviceinstancestatusid
   JOIN provisioning.serviceinstanceparameter sip ON 
si.serviceinstanceid = sip.fkserviceinstanceid
   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
  WHERE s.servicename = 'alert'::text AND p.name = 'countyNo'::text) p1
   JOIN ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
si."domain", si.fkaccountid AS accountid, p.value AS countystate, sis.status
              FROM provisioning.service s
         JOIN provisioning.serviceoffering so ON s.serviceid = 
so.fkserviceid
    JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
si.fkserviceofferingid
   JOIN provisioning.serviceinstancestatus sis ON 
si.fkserviceinstancestatusid = sis.serviceinstancestatusid
   JOIN provisioning.serviceinstanceparameter sip ON 
si.serviceinstanceid = sip.fkserviceinstanceid
   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
  WHERE s.servicename = 'alert'::text AND p.name = 'countyState'::text) 
p2 ON p1.accountid = p2.accountid AND p1.serviceinstanceid = 
p2.serviceinstanceid
   JOIN ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
si."domain", si.fkaccountid AS accountid, p.value AS listingtype, sis.status
         FROM provisioning.service s
    JOIN provisioning.serviceoffering so ON s.serviceid = so.fkserviceid
   JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
si.fkserviceofferingid
   JOIN provisioning.serviceinstancestatus sis ON 
si.fkserviceinstancestatusid = sis.serviceinstancestatusid
   JOIN provisioning.serviceinstanceparameter sip ON 
si.serviceinstanceid = sip.fkserviceinstanceid
   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
  WHERE s.servicename = 'alert'::text AND p.name = 'listingType'::text) 
p3 ON p2.accountid = p3.accountid AND p2.serviceinstanceid = 
p3.serviceinstanceid) services
ON a.accountid = services.accountid
ORDER BY services.serviceinstanceid;

Explain Analyze
------------------
explain analyze
select * from provisioning.alertserviceinstanceold where countystate = 
'FL' and countyno = '099' and status = 'ACTIVE' ;

                                                                                                                            
QUERY PLAN

----------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------
 Subquery Scan alertserviceinstanceold  (cost=31954.24..31954.25 rows=1 
width=328) (actual time=113485.801..113487.024 rows=110 loops=1)
   ->  Sort  (cost=31954.24..31954.24 rows=1 width=152) (actual 
time=113485.787..113486.123 rows=110 loops=1)
         Sort Key: si.serviceinstanceid
         ->  Hash Join  (cost=20636.38..31954.23 rows=1 width=152) 
(actual time=109721.688..113485.311 rows=110 loops=1)
               Hash Cond: ("outer".accountid = "inner".fkaccountid)
               ->  Hash Join  (cost=6595.89..16770.25 rows=228696 
width=47) (actual time=1742.592..4828.396 rows=229855 loops=1)
                     Hash Cond: ("outer".contactid = "inner".fkcontactid)
                     ->  Seq Scan on contact c  (cost=0.00..4456.96 
rows=228696 width=47) (actual time=0.006..1106.459 rows=229868 loops=1)
                     ->  Hash  (cost=6024.11..6024.11 rows=228711 
width=8) (actual time=1742.373..1742.373 rows=0 loops=1)
                           ->  Seq Scan on account a  
(cost=0.00..6024.11 rows=228711 width=8) (actual time=0.010..990.597 
rows=229855 loops=1)
               ->  Hash  (cost=14040.49..14040.49 rows=1 width=117) 
(actual time=107911.397..107911.397 rows=0 loops=1)
                     ->  Nested Loop  (cost=10.34..14040.49 rows=1 
width=117) (actual time=1185.383..107910.738 rows=110 loops=1)
                           ->  Nested Loop  (cost=10.34..14037.45 rows=1 
width=112) (actual time=1185.278..107898.885 rows=550 loops=1)
                                 ->  Hash Join  (cost=10.34..14033.98 
rows=1 width=124) (actual time=1185.224..107888.542 rows=110 loops=1)
                                       Hash Cond: 
("outer".fkserviceofferingid = "inner".serviceofferingid)
                                       ->  Hash Join  
(cost=7.96..14031.58 rows=1 width=128) (actual time=1184.490..107886.329 
rows=110 loops=1)
                                             Hash Cond: 
("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)
                                             ->  Nested Loop  
(cost=6.90..14030.50 rows=1 width=132) (actual time=1184.151..107884.302 
rows=110 loops=1)
                                                   Join Filter: 
("outer".fkaccountid = "inner".fkaccountid)
                                                   ->  Nested Loop  
(cost=6.90..14025.09 rows=1 width=116) (actual time=1184.123..107880.635 
rows=110 loops=1)
                                                         Join Filter: 
(("outer".fkaccountid = "inner".fkaccountid) AND 
("outer".serviceinstanceid = "inner".serviceinstanceid))
                                                         ->  Hash Join  
(cost=3.45..636.39 rows=1 width=95) (actual time=85.524..293.387 
rows=226 loops=1)
                                                               Hash 
Cond: ("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)
                                                               ->  Hash 
Join  (cost=2.38..635.29 rows=4 width=87) (actual time=6.894..289.000 
rows=663 loops=1)
                                                                     
Hash Cond: ("outer".fkserviceofferingid = "inner".serviceofferingid)
                                                                     ->  
Nested Loop  (cost=0.00..632.75 rows=23 width=91) (actual 
time=6.176..281.620 rows=663 loops=1)
                                                                           
->  Nested Loop  (cost=0.00..508.26 rows=23 width=13) (actual 
time=6.138..221.590 rows=663 loops=1)
                                                                                 
->  Index Scan using idx_parameter_value on parameter p  
(cost=0.00..437.42 rows=23 width=13) (actual time=6.091..20.656 rows=663 
loops=1)
                                                                                       
Index Cond: (value = '099'::text)
                                                                                       
Filter: (name = 'countyNo'::text)
                                                                                 
->  Index Scan using idx_serviceinstanceparameter_fkparameterid on 
serviceinstanceparameter sip  (cost=0.00..3.07 rows=1 width=8) (actual 
time=0.278..0.288 rows=1 loops=663)
                                                                                       
Index Cond: (sip.fkparameterid = "outer".parameterid)
                                                                           
->  Index Scan using pk_serviceinstance_serviceinstanceid on 
serviceinstance si  (cost=0.00..5.40 rows=1 width=78) (actual 
time=0.041..0.073 rows=1 loops=663)
                                                                                 
Index Cond: (si.serviceinstanceid = "outer".fkserviceinstanceid)
                                                                     ->  
Hash  (cost=2.38..2.38 rows=3 width=4) (actual time=0.445..0.445 rows=0 
loops=1)
                                                                           
->  Hash Join  (cost=1.08..2.38 rows=3 width=4) (actual 
time=0.314..0.426 rows=1 loops=1)
                                                                                 
Hash Cond: ("outer".fkserviceid = "inner".serviceid)
                                                                                 
->  Seq Scan on serviceoffering so  (cost=0.00..1.18 rows=18width=8) 
(actual time=0.005..0.065 rows=18 loops=1)
                                                                                 
->  Hash  (cost=1.07..1.07 rows=1 width=4) (actual time=0.033..0.033 
rows=0 loops=1)
                                                                                       
->  Seq Scan on service s  (cost=0.00..1.07 rows=1 width=4) (actual 
time=0.011..0.016 rows=1 loops=1)
                                                                                             
Filter: (servicename = 'alert'::text)
                                                               ->  Hash  
(cost=1.06..1.06 rows=1 width=16) (actual time=0.031..0.031 rows=0 loops=1)
                                                                     ->  
Seq Scan on serviceinstancestatus sis  (cost=0.00..1.06 rows=1 width=16) 
(actual time=0.008..0.014 rows=1 loops=1)
                                                                           
Filter: (status = 'ACTIVE'::text)
                                                         ->  Hash Join  
(cost=3.45..13386.23 rows=165 width=21) (actual time=0.119..461.891 
rows=3935 loops=226)
                                                               Hash 
Cond: ("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)
                                                               ->  Hash 
Join  (cost=2.38..13382.69 rows=165 width=25) (actual 
time=0.110..432.555 rows=3935 loops=226)
                                                                     
Hash Cond: ("outer".fkserviceofferingid = "inner".serviceofferingid)
                                                                     ->  
Nested Loop  (cost=0.00..13373.71 rows=990 width=29) (actual 
time=0.098..400.805 rows=3935 loops=226)
                                                                           
->  Nested Loop  (cost=0.00..8015.16 rows=990 width=13) (actual 
time=0.035..267.634 rows=3935 loops=226)
                                                                                 
->  Seq Scan on parameter p  (cost=0.00..4968.81 rows=989 width=13) 
(actual time=0.008..131.735 rows=3935 loops=226)
                                                                                       
Filter: ((name = 'countyState'::text) AND (value = 'FL'::text))
                                                                                 
->  Index Scan using idx_serviceinstanceparameter_fkparameterid on 
serviceinstanceparameter sip  (cost=0.00..3.07 rows=1 width=8) (actual 
time=0.015..0.020 rows=1 loops=889310)
                                                                                       
Index Cond: (sip.fkparameterid = "outer".parameterid)
                                                                           
->  Index Scan using pk_serviceinstance_serviceinstanceid on 
serviceinstance si  (cost=0.00..5.40 rows=1 width=16) (actual 
time=0.012..0.019 rows=1 loops=889310)
                                                                                 
Index Cond: (si.serviceinstanceid = "outer".fkserviceinstanceid)
                                                                     ->  
Hash  (cost=2.38..2.38 rows=3 width=4) (actual time=0.439..0.439 rows=0 
loops=1)
                                                                           
->  Hash Join  (cost=1.08..2.38 rows=3 width=4) (actual 
time=0.310..0.423 rows=1 loops=1)
                                                                                 
Hash Cond: ("outer".fkserviceid = "inner".serviceid)
                                                                                 
->  Seq Scan on serviceoffering so  (cost=0.00..1.18 rows=18 width=8) 
(actual time=0.006..0.065 rows=18 loops=1)
                                                                                 
->  Hash  (cost=1.07..1.07 rows=1 width=4) (actual time=0.035..0.035 
rows=0 loops=1)
                                                                                       
->  Seq Scan on service s  (cost=0.00..1.07 rows=1 width=4) (actual 
time=0.013..0.018 rows=1 loops=1)
                                                                                             
Filter: (servicename = 'alert'::text)
                                                               ->  Hash  
(cost=1.05..1.05 rows=5 width=4) (actual time=0.059..0.059 rows=0 loops=1)
                                                                     ->  
Seq Scan on serviceinstancestatus sis  (cost=0.00..1.05 rows=5 width=4) 
(actual time=0.010..0.029 rows=5 loops=1)
                                                   ->  Index Scan using 
pk_serviceinstance_serviceinstanceid on serviceinstance si  
(cost=0.00..5.40 rows=1 width=16) (actual time=0.009..0.012 rows=1 
loops=110)
                                                         Index Cond: 
(si.serviceinstanceid = "outer".fkserviceinstanceid)
                                             ->  Hash  (cost=1.05..1.05 
rows=5 width=4) (actual time=0.055..0.055 rows=0 loops=1)
                                                   ->  Seq Scan on 
serviceinstancestatus sis  (cost=0.00..1.05 rows=5 width=4) (actual 
time=0.008..0.025 rows=5 loops=1)
                                       ->  Hash  (cost=2.38..2.38 rows=3 
width=4) (actual time=0.461..0.461 rows=0 loops=1)
                                             ->  Hash Join  
(cost=1.08..2.38 rows=3 width=4) (actual time=0.325..0.445 rows=1 loops=1)
                                                   Hash Cond: 
("outer".fkserviceid = "inner".serviceid)
                                                   ->  Seq Scan on 
serviceoffering so  (cost=0.00..1.18 rows=18 width=8) (actual 
time=0.006..0.074 rows=18 loops=1)
                                                   ->  Hash  
(cost=1.07..1.07 rows=1 width=4) (actual time=0.044..0.044 rows=0 loops=1)
                                                         ->  Seq Scan on 
service s  (cost=0.00..1.07 rows=1 width=4) (actual time=0.022..0.027 
rows=1 loops=1)
                                                               Filter: 
(servicename = 'alert'::text)
                                 ->  Index Scan using 
idx_serviceinstanceparameter_fkserviceinstanceid on 
serviceinstanceparameter sip  (cost=0.00..3.41 rows=5 width=8) (actual 
time=0.018..0.038 rows=5 loops=110)
                                       Index Cond: 
(sip.fkserviceinstanceid = "outer".fkserviceinstanceid)
                           ->  Index Scan using pk_parameter_parameterid 
on parameter p  (cost=0.00..3.02 rows=1 width=13) (actual 
time=0.011..0.012 rows=0 loops=550)
                                 Index Cond: ("outer".fkparameterid = 
p.parameterid)
                                 Filter: (name = 'listingType'::text)

 Total runtime: 113490.582 ms
(82 rows)



Tom Lane wrote:
>Pallav Kalva <pkalva@livedatagroup.com> writes:
>  
>>   I am having problem optimizing this query,
>>    
>
>Get rid of the un-optimizable function inside the view.  You've
>converted something that should be a join into an unreasonably large
>number of function calls.
>
>  
>>                    ->  Seq Scan on serviceinstance si  
>>(cost=0.00..15831.52 rows=7 width=78) (actual time=174.430..18948.210 
>>rows=358 loops=1)
>>                          Filter: (((subplan) = 'FL'::text) AND 
>>((subplan) = '099'::text))
>>                          SubPlan
>>                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
>>(actual time=0.090..0.093 rows=1 loops=3923)
>>                            ->  Result  (cost=0.00..0.01 rows=1 width=0) 
>>(actual time=0.058..0.061 rows=1 loops=265617)
>>    
>
>The bulk of the cost here is in the second subplan (0.061 * 265617 =
>16202.637 msec total runtime), and there's not a darn thing Postgres
>can do to improve this because the work is all down inside a "black box"
>function.  In fact the planner does not even know that the function call
>is expensive, else it would have preferred a plan that requires fewer
>evaluations of the function.  The alternative plan you show is *not*
>faster "because it's an indexscan"; it's faster because get_parametervalue
>is evaluated fewer times.
>
>The useless sub-SELECTs atop the function calls are adding their own
>little increment of wasted time, too.  I'm not sure how bad that is
>relative to the function calls, but it's certainly not helping.
>
>			regards, tom lane
>
>  


From pgsql-performance-owner@postgresql.org  Wed Jan 11 13:06:55 2006
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Date: Wed, 11 Jan 2006 10:06:45 -0700
From: Michael Fuhr <mike@fuhr.org>
To: Robert Creager <Robert_Creager@LogicalChaos.org>
Cc: PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Index isn't used during a join.
Message-ID: <20060111170645.GA58041@winnie.fuhr.org>
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On Wed, Jan 11, 2006 at 08:02:37AM -0700, Robert Creager wrote:
> The query is wrong as stated, as it won't work when the interval
> crosses a year boundary, but it's a stop gap for now.

Yeah, I realized that shortly after I posted the original and posted
a correction.

http://archives.postgresql.org/pgsql-performance/2006-01/msg00104.php

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 14:25:53 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Andy <frum@ar-sd.net>
Cc: Frank Wiles <frank@wiles.org>, pgsql-performance@postgresql.org
Subject: Re: Improving Inner Join Performance
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Did you originally post some problem queries? The settings look OK,
though 1G of memory isn't very much now-a-days.

On Mon, Jan 09, 2006 at 09:56:52AM +0200, Andy wrote:
> shared_buffers = 10240
> effective_cache_size = 64000
> RAM on server: 1Gb. 
> 
> Andy.
> 
> ----- Original Message ----- 
> 
> From: "Frank Wiles" <frank@wiles.org>
> To: "Andy" <frum@ar-sd.net>
> Sent: Friday, January 06, 2006 7:12 PM
> Subject: Re: [PERFORM] Improving Inner Join Performance
> 
> 
> > On Fri, 6 Jan 2006 09:59:30 +0200
> > "Andy" <frum@ar-sd.net> wrote:
> > 
> >> Yes I have indexes an all join fields. 
> >> The tables have around 30 columns each and around 100k rows. 
> >> The database is vacuumed every hour.  
> > 
> >  What are you settings for: 
> > 
> >  shared_buffers 
> >  effective_cache_size
> > 
> >  And how much RAM do you have in the server? 
> > 
> > ---------------------------------
> >   Frank Wiles <frank@wiles.org>
> >   http://www.wiles.org
> > ---------------------------------
> > 
> > 
> >

-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 11 14:40:40 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Andrea Arcangeli <andrea@cpushare.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Tue, Jan 10, 2006 at 02:44:47AM +0100, Andrea Arcangeli wrote:
> "cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
> "preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference

One thing you could do is change the like to:

WHERE position(' PREEMPT ' in kernel_version) != 0

And then create a functional index on that:

CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 11 15:02:13 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Pallav Kalva <pkalva@livedatagroup.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	PGPerformance <pgsql-performance@postgresql.org>
Subject: Re: Postgres8.0 planner chooses WRONG plan
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On Wed, Jan 11, 2006 at 11:44:58AM -0500, Pallav Kalva wrote:
Some view you've got there... you might want to break that apart into
multiple views that are a bit easier to manage.
service_instance_with_status is a likely candidate, for example.

> View Definition
> -------------------
> 
> create or replace view provisioning.alertserviceinstanceold as
> SELECT services.serviceinstanceid, a.accountid, c.firstname, c.lastname, 
> c.email, services.countyno, services.countystate, services.listingtype 
> AS listingtypename, services.status, services.affiliate, 
> services.affiliatesub, services."domain"
>   FROM provisioning.account a
>   JOIN common.contact c ON a.fkcontactid = c.contactid
>   JOIN ( SELECT p1.serviceinstanceid, p1.accountid, p1.countyno, 
> p2.countystate, p3.listingtype, p1.status, p1.affiliate, 
> p1.affiliatesub, p1."domain"
>      FROM ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
> si."domain", si.fkaccountid AS accountid, p.value AS countyno, sis.status
>              FROM provisioning.service s
>         JOIN provisioning.serviceoffering so ON s.serviceid = 
> so.fkserviceid
>    JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
> si.fkserviceofferingid
>   JOIN provisioning.serviceinstancestatus sis ON 
> si.fkserviceinstancestatusid = sis.serviceinstancestatusid
>   JOIN provisioning.serviceinstanceparameter sip ON 
> si.serviceinstanceid = sip.fkserviceinstanceid
>   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
>  WHERE s.servicename = 'alert'::text AND p.name = 'countyNo'::text) p1
>   JOIN ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
> si."domain", si.fkaccountid AS accountid, p.value AS countystate, sis.status
>              FROM provisioning.service s
>         JOIN provisioning.serviceoffering so ON s.serviceid = 
> so.fkserviceid
>    JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
> si.fkserviceofferingid
>   JOIN provisioning.serviceinstancestatus sis ON 
> si.fkserviceinstancestatusid = sis.serviceinstancestatusid
>   JOIN provisioning.serviceinstanceparameter sip ON 
> si.serviceinstanceid = sip.fkserviceinstanceid
>   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
>  WHERE s.servicename = 'alert'::text AND p.name = 'countyState'::text) 
> p2 ON p1.accountid = p2.accountid AND p1.serviceinstanceid = 
> p2.serviceinstanceid
>   JOIN ( SELECT si.serviceinstanceid, si.affiliate, si.affiliatesub, 
> si."domain", si.fkaccountid AS accountid, p.value AS listingtype, sis.status
>         FROM provisioning.service s
>    JOIN provisioning.serviceoffering so ON s.serviceid = so.fkserviceid
>   JOIN provisioning.serviceinstance si ON so.serviceofferingid = 
> si.fkserviceofferingid
>   JOIN provisioning.serviceinstancestatus sis ON 
> si.fkserviceinstancestatusid = sis.serviceinstancestatusid
>   JOIN provisioning.serviceinstanceparameter sip ON 
> si.serviceinstanceid = sip.fkserviceinstanceid
>   JOIN common.parameter p ON sip.fkparameterid = p.parameterid
>  WHERE s.servicename = 'alert'::text AND p.name = 'listingType'::text) 
> p3 ON p2.accountid = p3.accountid AND p2.serviceinstanceid = 
> p3.serviceinstanceid) services
> ON a.accountid = services.accountid
> ORDER BY services.serviceinstanceid;
> 
> Explain Analyze
> ------------------
> explain analyze
> select * from provisioning.alertserviceinstanceold where countystate = 
> 'FL' and countyno = '099' and status = 'ACTIVE' ;
> 
>                                                                                                                            
> QUERY PLAN
> 
> ----------------------------------------------------------------------------------------------------------------------------------------------
> --------------------------------------------------------------------------------------------------------------------
> Subquery Scan alertserviceinstanceold  (cost=31954.24..31954.25 rows=1 
> width=328) (actual time=113485.801..113487.024 rows=110 loops=1)
>   ->  Sort  (cost=31954.24..31954.24 rows=1 width=152) (actual 
> time=113485.787..113486.123 rows=110 loops=1)
>         Sort Key: si.serviceinstanceid
>         ->  Hash Join  (cost=20636.38..31954.23 rows=1 width=152) 
> (actual time=109721.688..113485.311 rows=110 loops=1)
>               Hash Cond: ("outer".accountid = "inner".fkaccountid)
>               ->  Hash Join  (cost=6595.89..16770.25 rows=228696 
> width=47) (actual time=1742.592..4828.396 rows=229855 loops=1)
>                     Hash Cond: ("outer".contactid = "inner".fkcontactid)
>                     ->  Seq Scan on contact c  (cost=0.00..4456.96 
> rows=228696 width=47) (actual time=0.006..1106.459 rows=229868 loops=1)
>                     ->  Hash  (cost=6024.11..6024.11 rows=228711 
> width=8) (actual time=1742.373..1742.373 rows=0 loops=1)
>                           ->  Seq Scan on account a  
> (cost=0.00..6024.11 rows=228711 width=8) (actual time=0.010..990.597 
> rows=229855 loops=1)
>               ->  Hash  (cost=14040.49..14040.49 rows=1 width=117) 
> (actual time=107911.397..107911.397 rows=0 loops=1)
>                     ->  Nested Loop  (cost=10.34..14040.49 rows=1 
> width=117) (actual time=1185.383..107910.738 rows=110 loops=1)
>                           ->  Nested Loop  (cost=10.34..14037.45 rows=1 
> width=112) (actual time=1185.278..107898.885 rows=550 loops=1)
>                                 ->  Hash Join  (cost=10.34..14033.98 
> rows=1 width=124) (actual time=1185.224..107888.542 rows=110 loops=1)
>                                       Hash Cond: 
> ("outer".fkserviceofferingid = "inner".serviceofferingid)
>                                       ->  Hash Join  
> (cost=7.96..14031.58 rows=1 width=128) (actual time=1184.490..107886.329 
> rows=110 loops=1)
>                                             Hash Cond: 
> ("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)
>                                             ->  Nested Loop  
> (cost=6.90..14030.50 rows=1 width=132) (actual time=1184.151..107884.302 
> rows=110 loops=1)
>                                                   Join Filter: 
> ("outer".fkaccountid = "inner".fkaccountid)

Well, here's the step that's killing you:
>                                                   ->  Nested Loop  
> (cost=6.90..14025.09 rows=1 width=116) (actual time=1184.123..107880.635 
> rows=110 loops=1)
>                                                         Join Filter: 
> (("outer".fkaccountid = "inner".fkaccountid) AND 
> ("outer".serviceinstanceid = "inner".serviceinstanceid))
>                                                         ->  Hash Join  
> (cost=3.45..636.39 rows=1 width=95) (actual time=85.524..293.387 
> rows=226 loops=1)
>                                                               Hash 
> Cond: ("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)

Unfortunately, the way this query plan came out it's difficult to figure
out what the other input to that nested loop is. But before we get to
that, what do you have join_collapse_limit set to? If it's the default
of 8 then the optimizer is essentially going to follow the join order
you specified when you wrote the view, which could be far from optimal.
It would be worth setting join_collapse_limit high enough so that this
query will get flattened and see what kind of plan it comes up with
then. Note that this could result in an unreasonably-large plan time,
but if it results in a fast query execution we know it's just a matter
of re-ordering things in the query.

Also, it would be best if you could send the results of explain as an
attachement that hasn't been word-wrapped.

>                                                               ->  Hash 
> Join  (cost=2.38..635.29 rows=4 width=87) (actual time=6.894..289.000 
> rows=663 loops=1)
>                                                                     
> Hash Cond: ("outer".fkserviceofferingid = "inner".serviceofferingid)
>                                                                     ->  
> Nested Loop  (cost=0.00..632.75 rows=23 width=91) (actual 
> time=6.176..281.620 rows=663 loops=1)
>                                                                           
> ->  Nested Loop  (cost=0.00..508.26 rows=23 width=13) (actual 
> time=6.138..221.590 rows=663 loops=1)
>                                                                                 
> ->  Index Scan using idx_parameter_value on parameter p  
> (cost=0.00..437.42 rows=23 width=13) (actual time=6.091..20.656 rows=663 
> loops=1)
>                                                                                       
> Index Cond: (value = '099'::text)
>                                                                                       
> Filter: (name = 'countyNo'::text)
>                                                                                 
> ->  Index Scan using idx_serviceinstanceparameter_fkparameterid on 
> serviceinstanceparameter sip  (cost=0.00..3.07 rows=1 width=8) (actual 
> time=0.278..0.288 rows=1 loops=663)
>                                                                                       
> Index Cond: (sip.fkparameterid = "outer".parameterid)
>                                                                           
> ->  Index Scan using pk_serviceinstance_serviceinstanceid on 
> serviceinstance si  (cost=0.00..5.40 rows=1 width=78) (actual 
> time=0.041..0.073 rows=1 loops=663)
>                                                                                 
> Index Cond: (si.serviceinstanceid = "outer".fkserviceinstanceid)
>                                                                     ->  
> Hash  (cost=2.38..2.38 rows=3 width=4) (actual time=0.445..0.445 rows=0 
> loops=1)
>                                                                           
> ->  Hash Join  (cost=1.08..2.38 rows=3 width=4) (actual 
> time=0.314..0.426 rows=1 loops=1)
>                                                                                 
> Hash Cond: ("outer".fkserviceid = "inner".serviceid)
>                                                                                 
> ->  Seq Scan on serviceoffering so  (cost=0.00..1.18 rows=18width=8) 
> (actual time=0.005..0.065 rows=18 loops=1)
>                                                                                 
> ->  Hash  (cost=1.07..1.07 rows=1 width=4) (actual time=0.033..0.033 
> rows=0 loops=1)
>                                                                                       
> ->  Seq Scan on service s  (cost=0.00..1.07 rows=1 width=4) (actual 
> time=0.011..0.016 rows=1 loops=1)
>                                                                                             
> Filter: (servicename = 'alert'::text)
>                                                               ->  Hash  
> (cost=1.06..1.06 rows=1 width=16) (actual time=0.031..0.031 rows=0 loops=1)
>                                                                     ->  
> Seq Scan on serviceinstancestatus sis  (cost=0.00..1.06 rows=1 width=16) 
> (actual time=0.008..0.014 rows=1 loops=1)
>                                                                           
> Filter: (status = 'ACTIVE'::text)
>                                                         ->  Hash Join  
> (cost=3.45..13386.23 rows=165 width=21) (actual time=0.119..461.891 
> rows=3935 loops=226)
>                                                               Hash 
> Cond: ("outer".fkserviceinstancestatusid = "inner".serviceinstancestatusid)
>                                                               ->  Hash 
> Join  (cost=2.38..13382.69 rows=165 width=25) (actual 
> time=0.110..432.555 rows=3935 loops=226)
>                                                                     
> Hash Cond: ("outer".fkserviceofferingid = "inner".serviceofferingid)
>                                                                     ->  
> Nested Loop  (cost=0.00..13373.71 rows=990 width=29) (actual 
> time=0.098..400.805 rows=3935 loops=226)
>                                                                           
> ->  Nested Loop  (cost=0.00..8015.16 rows=990 width=13) (actual 
> time=0.035..267.634 rows=3935 loops=226)
>                                                                                 
> ->  Seq Scan on parameter p  (cost=0.00..4968.81 rows=989 width=13) 
> (actual time=0.008..131.735 rows=3935 loops=226)
>                                                                                       
> Filter: ((name = 'countyState'::text) AND (value = 'FL'::text))
>                                                                                 
> ->  Index Scan using idx_serviceinstanceparameter_fkparameterid on 
> serviceinstanceparameter sip  (cost=0.00..3.07 rows=1 width=8) (actual 
> time=0.015..0.020 rows=1 loops=889310)
>                                                                                       
> Index Cond: (sip.fkparameterid = "outer".parameterid)
>                                                                           
> ->  Index Scan using pk_serviceinstance_serviceinstanceid on 
> serviceinstance si  (cost=0.00..5.40 rows=1 width=16) (actual 
> time=0.012..0.019 rows=1 loops=889310)
>                                                                                 
> Index Cond: (si.serviceinstanceid = "outer".fkserviceinstanceid)
>                                                                     ->  
> Hash  (cost=2.38..2.38 rows=3 width=4) (actual time=0.439..0.439 rows=0 
> loops=1)
>                                                                           
> ->  Hash Join  (cost=1.08..2.38 rows=3 width=4) (actual 
> time=0.310..0.423 rows=1 loops=1)
>                                                                                 
> Hash Cond: ("outer".fkserviceid = "inner".serviceid)
>                                                                                 
> ->  Seq Scan on serviceoffering so  (cost=0.00..1.18 rows=18 width=8) 
> (actual time=0.006..0.065 rows=18 loops=1)
>                                                                                 
> ->  Hash  (cost=1.07..1.07 rows=1 width=4) (actual time=0.035..0.035 
> rows=0 loops=1)
>                                                                                       
> ->  Seq Scan on service s  (cost=0.00..1.07 rows=1 width=4) (actual 
> time=0.013..0.018 rows=1 loops=1)
>                                                                                             
> Filter: (servicename = 'alert'::text)
>                                                               ->  Hash  
> (cost=1.05..1.05 rows=5 width=4) (actual time=0.059..0.059 rows=0 loops=1)
>                                                                     ->  
> Seq Scan on serviceinstancestatus sis  (cost=0.00..1.05 rows=5 width=4) 
> (actual time=0.010..0.029 rows=5 loops=1)
>                                                   ->  Index Scan using 
> pk_serviceinstance_serviceinstanceid on serviceinstance si  
> (cost=0.00..5.40 rows=1 width=16) (actual time=0.009..0.012 rows=1 
> loops=110)
>                                                         Index Cond: 
> (si.serviceinstanceid = "outer".fkserviceinstanceid)
>                                             ->  Hash  (cost=1.05..1.05 
> rows=5 width=4) (actual time=0.055..0.055 rows=0 loops=1)
>                                                   ->  Seq Scan on 
> serviceinstancestatus sis  (cost=0.00..1.05 rows=5 width=4) (actual 
> time=0.008..0.025 rows=5 loops=1)
>                                       ->  Hash  (cost=2.38..2.38 rows=3 
> width=4) (actual time=0.461..0.461 rows=0 loops=1)
>                                             ->  Hash Join  
> (cost=1.08..2.38 rows=3 width=4) (actual time=0.325..0.445 rows=1 loops=1)
>                                                   Hash Cond: 
> ("outer".fkserviceid = "inner".serviceid)
>                                                   ->  Seq Scan on 
> serviceoffering so  (cost=0.00..1.18 rows=18 width=8) (actual 
> time=0.006..0.074 rows=18 loops=1)
>                                                   ->  Hash  
> (cost=1.07..1.07 rows=1 width=4) (actual time=0.044..0.044 rows=0 loops=1)
>                                                         ->  Seq Scan on 
> service s  (cost=0.00..1.07 rows=1 width=4) (actual time=0.022..0.027 
> rows=1 loops=1)
>                                                               Filter: 
> (servicename = 'alert'::text)
>                                 ->  Index Scan using 
> idx_serviceinstanceparameter_fkserviceinstanceid on 
> serviceinstanceparameter sip  (cost=0.00..3.41 rows=5 width=8) (actual 
> time=0.018..0.038 rows=5 loops=110)
>                                       Index Cond: 
> (sip.fkserviceinstanceid = "outer".fkserviceinstanceid)
>                           ->  Index Scan using pk_parameter_parameterid 
> on parameter p  (cost=0.00..3.02 rows=1 width=13) (actual 
> time=0.011..0.012 rows=0 loops=550)
>                                 Index Cond: ("outer".fkparameterid = 
> p.parameterid)
>                                 Filter: (name = 'listingType'::text)
> 
> Total runtime: 113490.582 ms
> (82 rows)
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Sat Jan 14 01:50:24 2006
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	<jean-philippe.cote@crt.umontreal.ca>
To: <pgsql-performance@postgresql.org>
Subject: Extremely irregular query performance
Date: Wed, 11 Jan 2006 14:29:03 -0500
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Hi,

I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's)
with 4Gb of RAM. I have recently noticed that the performance of
some more complex queries is extremely variable and irregular.
For example, I currently have a query that returns a small number 
of rows (5) by joining a dozen of tables. Below are the running times
obtained by repeatedly lauching this query in psql:

Time: 424.848 ms
Time: 1615.143 ms
Time: 15036.475 ms
Time: 83471.683 ms
Time: 163.224 ms
Time: 2454.939 ms
Time: 188.093 ms
Time: 158.071 ms
Time: 192.431 ms
Time: 195.076 ms
Time: 635.739 ms
Time: 164549.902 ms

As you can see, the performance is most of the time pretty good (less
than 1 second), but every fourth of fifth time I launch the query
the server seems to go into orbit. For the longer running times,
I can see from top that the server process uses almost 100% of
a CPU.

This is rather worrisome, as I cannot be confident of the overall performance
of my application with so much variance in query response times.

I suspect a configuration problem related to the cache mechanism 
(shared_buffers? effective_cache_size?), but to be honest I do not know 
where to start to diagnose it. 

Any help would be greatly appreciated.

Thanks in advance,

J-P


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From: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
Subject: Re: Slow query with joins 
Date: Wed, 11 Jan 2006 20:55:32 +0100
To: pgsql-performance@postgresql.org
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Yes,  the rowcount estimates are real, however, it has been a long  
time since the last VACUUM FULL (there is never a good time).

I have clustered the tables, reindexed, analyzed, vacuumed and the  
plan now looks like this:


no_people=# explain SELECT r.id AS r_id, r.firstname || ' ' ||  
r.lastname AS r_name, ad.id AS ad_id, ad.type AS ad_type, ad.address  
AS ad_address, ad.postalcode AS ad_postalcode, ad.postalsite AS  
ad_postalsite, ad.priority AS ad_priority, ad.position[0] AS ad_lat,  
ad.position[1] AS ad_lon, ad.uncertainty AS ad_uncertainty, ad.extra  
AS ad_extra, ad.deleted AS ad_deleted, co.id AS co_id, co.type AS  
co_type, co.value AS co_value, co.description AS co_description,  
co.priority AS co_priority, co.visible AS co_visible, co.searchable  
AS co_searchable, co.deleted AS co_deleted FROM people r LEFT OUTER  
JOIN addresses ad ON(r.id = ad.record) LEFT OUTER JOIN contacts co ON 
(r.id = co.record) WHERE NOT r.deleted AND  r.original IS NULL ORDER  
BY r.id;
                                                         QUERY PLAN
------------------------------------------------------------------------ 
--------------------------------------------------
Sort  (cost=182866.49..182943.12 rows=30655 width=587)
    Sort Key: r.id
    ->  Nested Loop Left Join  (cost=0.00..170552.10 rows=30655  
width=587)
          ->  Nested Loop Left Join  (cost=0.00..75054.96 rows=26325  
width=160)
                ->  Index Scan using people_deleted_original_is_null  
on people r  (cost=0.00..1045.47 rows=23861 width=27)
                      Filter: ((NOT deleted) AND (original IS NULL))
                ->  Index Scan using addresses_record_idx on  
addresses ad  (cost=0.00..3.05 rows=4 width=137)
                      Index Cond: ("outer".id = ad.record)
          ->  Index Scan using contacts_record_idx on contacts co   
(cost=0.00..3.32 rows=24 width=431)
                Index Cond: ("outer".id = co.record)
(10 rows)






Looks faster, but still very slow. I added limit 1000 and it has been  
running for about 25 minutes now with no output. top shows:


   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
29994 postgres  18   0 95768  78m  68m R 17.0  7.7   0:53.27 postmaster



which is unusual, I usually get 99.9 %cpu for just about any query,  
which leads me to believe this is disk related.



postgresql.conf:
shared_buffers = 8192
work_mem = 8192
maintenance_work_mem = 524288




Hardware 2x2.8GHz cpu
1GB ram

Could this be an issue related to lack of VACUUM FULL? The tables get  
a lot of updates.


Thank you very much so far!




On Jan 11, 2006, at 4:45 PM, Tom Lane wrote:

> Bendik Rognlien Johansen <bendik.johansen@gmail.com> writes:
>> Has anyone got any tips for speeding up this query? It currently
>> takes hours to start.
>
> Are the rowcount estimates close to reality?  The plan doesn't look
> unreasonable to me if they are.  It might help to increase work_mem
> to ensure that the hash tables don't spill to disk.
>
> Indexes:
>      "people_original_is_null" btree (original) WHERE original IS NULL
>
> This index seems poorly designed: the actual index entries are dead
> weight since all of them are necessarily NULL.  You might as well make
> the index carry something that you frequently test in conjunction with
> "original IS NULL".  For instance, if this particular query is a  
> common
> case, you could replace this index with
>
> CREATE INDEX people_deleted_original_is_null ON people(deleted)
>   WHERE original IS NULL;
>
> This index is still perfectly usable for queries that only say  
> "original
> IS NULL", but it can also filter out rows with the wrong value of
> deleted.  Now, if there are hardly any rows with deleted = true, maybe
> this won't help much for your problem.  But in any case you ought to
> consider whether you can make the index entries do something useful.
>
> 			regards, tom lane


From pgsql-performance-owner@postgresql.org  Wed Jan 11 16:24:07 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Slow query with joins
Message-ID: <20060111202345.GC63175@pervasive.com>
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	<13028.1136994347@sss.pgh.pa.us>
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I'd try figuring out if the join is the culprit or the sort is (by
dropping the ORDER BY). work_mem is probably forcing the sort to spill
to disk, and if your drives are rather busy...

You might also get a win if you re-order the joins to people, contacts,
addresses, if you know it will have the same result.

In this case LIMIT won't have any real effect, because you have to go
all the way through with the ORDER BY anyway.

On Wed, Jan 11, 2006 at 08:55:32PM +0100, Bendik Rognlien Johansen wrote:
> Yes,  the rowcount estimates are real, however, it has been a long  
> time since the last VACUUM FULL (there is never a good time).
> 
> I have clustered the tables, reindexed, analyzed, vacuumed and the  
> plan now looks like this:
> 
> 
> no_people=# explain SELECT r.id AS r_id, r.firstname || ' ' ||  
> r.lastname AS r_name, ad.id AS ad_id, ad.type AS ad_type, ad.address  
> AS ad_address, ad.postalcode AS ad_postalcode, ad.postalsite AS  
> ad_postalsite, ad.priority AS ad_priority, ad.position[0] AS ad_lat,  
> ad.position[1] AS ad_lon, ad.uncertainty AS ad_uncertainty, ad.extra  
> AS ad_extra, ad.deleted AS ad_deleted, co.id AS co_id, co.type AS  
> co_type, co.value AS co_value, co.description AS co_description,  
> co.priority AS co_priority, co.visible AS co_visible, co.searchable  
> AS co_searchable, co.deleted AS co_deleted FROM people r LEFT OUTER  
> JOIN addresses ad ON(r.id = ad.record) LEFT OUTER JOIN contacts co ON 
> (r.id = co.record) WHERE NOT r.deleted AND  r.original IS NULL ORDER  
> BY r.id;
>                                                         QUERY PLAN
> ------------------------------------------------------------------------ 
> --------------------------------------------------
> Sort  (cost=182866.49..182943.12 rows=30655 width=587)
>    Sort Key: r.id
>    ->  Nested Loop Left Join  (cost=0.00..170552.10 rows=30655  
> width=587)
>          ->  Nested Loop Left Join  (cost=0.00..75054.96 rows=26325  
> width=160)
>                ->  Index Scan using people_deleted_original_is_null  
> on people r  (cost=0.00..1045.47 rows=23861 width=27)
>                      Filter: ((NOT deleted) AND (original IS NULL))
>                ->  Index Scan using addresses_record_idx on  
> addresses ad  (cost=0.00..3.05 rows=4 width=137)
>                      Index Cond: ("outer".id = ad.record)
>          ->  Index Scan using contacts_record_idx on contacts co   
> (cost=0.00..3.32 rows=24 width=431)
>                Index Cond: ("outer".id = co.record)
> (10 rows)
> 
> 
> 
> 
> 
> 
> Looks faster, but still very slow. I added limit 1000 and it has been  
> running for about 25 minutes now with no output. top shows:
> 
> 
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 29994 postgres  18   0 95768  78m  68m R 17.0  7.7   0:53.27 postmaster
> 
> 
> 
> which is unusual, I usually get 99.9 %cpu for just about any query,  
> which leads me to believe this is disk related.
> 
> 
> 
> postgresql.conf:
> shared_buffers = 8192
> work_mem = 8192
> maintenance_work_mem = 524288
> 
> 
> 
> 
> Hardware 2x2.8GHz cpu
> 1GB ram
> 
> Could this be an issue related to lack of VACUUM FULL? The tables get  
> a lot of updates.
> 
> 
> Thank you very much so far!
> 
> 
> 
> 
> On Jan 11, 2006, at 4:45 PM, Tom Lane wrote:
> 
> >Bendik Rognlien Johansen <bendik.johansen@gmail.com> writes:
> >>Has anyone got any tips for speeding up this query? It currently
> >>takes hours to start.
> >
> >Are the rowcount estimates close to reality?  The plan doesn't look
> >unreasonable to me if they are.  It might help to increase work_mem
> >to ensure that the hash tables don't spill to disk.
> >
> >Indexes:
> >     "people_original_is_null" btree (original) WHERE original IS NULL
> >
> >This index seems poorly designed: the actual index entries are dead
> >weight since all of them are necessarily NULL.  You might as well make
> >the index carry something that you frequently test in conjunction with
> >"original IS NULL".  For instance, if this particular query is a  
> >common
> >case, you could replace this index with
> >
> >CREATE INDEX people_deleted_original_is_null ON people(deleted)
> >  WHERE original IS NULL;
> >
> >This index is still perfectly usable for queries that only say  
> >"original
> >IS NULL", but it can also filter out rows with the wrong value of
> >deleted.  Now, if there are hardly any rows with deleted = true, maybe
> >this won't help much for your problem.  But in any case you ought to
> >consider whether you can make the index entries do something useful.
> >
> >			regards, tom lane
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
> 

-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 11 16:39:51 2006
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From: Andrea Arcangeli <andrea@cpushare.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Wed, Jan 11, 2006 at 12:40:32PM -0600, Jim C. Nasby wrote:
> On Tue, Jan 10, 2006 at 02:44:47AM +0100, Andrea Arcangeli wrote:
> > "cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
> > "preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference
> 
> One thing you could do is change the like to:
> 
> WHERE position(' PREEMPT ' in kernel_version) != 0

That alone fixed it, with this I don't even need the index (yet). Thanks
a lot.

> And then create a functional index on that:
> 
> CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );

The index only helps the above query with = 0 and not the one with != 0,
but it seems not needed in practice.

From pgsql-performance-owner@postgresql.org  Wed Jan 11 16:46:44 2006
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Cc: "Jim C. Nasby" <jnasby@pervasive.com>, pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Wed, Jan 11, 2006 at 09:39:47PM +0100, Andrea Arcangeli wrote:
> On Wed, Jan 11, 2006 at 12:40:32PM -0600, Jim C. Nasby wrote:
> > On Tue, Jan 10, 2006 at 02:44:47AM +0100, Andrea Arcangeli wrote:
> > > "cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
> > > "preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference
> > 
> > One thing you could do is change the like to:
> > 
> > WHERE position(' PREEMPT ' in kernel_version) != 0
> 
> That alone fixed it, with this I don't even need the index (yet). Thanks
> a lot.

The fix is online already w/o index:

	http://klive.cpushare.com/?branch=all&scheduler=preemptive

Of course I'm still fully available to test any fix for the previous
LIKE query if there's interest.

From pgsql-performance-owner@postgresql.org  Wed Jan 11 17:02:27 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Andrea Arcangeli <andrea@cpushare.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
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On Wed, Jan 11, 2006 at 09:39:47PM +0100, Andrea Arcangeli wrote:
> > CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );
> 
> The index only helps the above query with = 0 and not the one with != 0,
> but it seems not needed in practice.

Hrm. If you need indexing then, you'll probably have to do 2 indexes
with a WHERE clause...

CREATE INDEX ... WHERE position(...) = 0;
CREATE INDEX ... WHERE position(...) != 0;

I suspect this is because of a lack of stats for functional indexes.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 11 17:13:24 2006
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Subject: Re: NOT LIKE much faster than LIKE? 
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Comments: In-reply-to "Jim C. Nasby" <jnasby@pervasive.com>
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"Jim C. Nasby" <jnasby@pervasive.com> writes:
> On Wed, Jan 11, 2006 at 09:39:47PM +0100, Andrea Arcangeli wrote:
>> The index only helps the above query with = 0 and not the one with != 0,
>> but it seems not needed in practice.

> I suspect this is because of a lack of stats for functional indexes.

No, it's because != isn't an indexable operator.

			regards, tom lane

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From: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
Subject: Re: Slow query with joins
Date: Wed, 11 Jan 2006 22:30:58 +0100
To: "Jim C. Nasby" <jnasby@pervasive.com>
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The sort is definitively the culprit. When I removed it the query was  
instant. I tried setting work_mem = 131072 but it did not seem to  
help. I really don't understand this :-( Any other ideas?

Thanks!


On Jan 11, 2006, at 9:23 PM, Jim C. Nasby wrote:

> I'd try figuring out if the join is the culprit or the sort is (by
> dropping the ORDER BY). work_mem is probably forcing the sort to spill
> to disk, and if your drives are rather busy...
>
> You might also get a win if you re-order the joins to people,  
> contacts,
> addresses, if you know it will have the same result.
>
> In this case LIMIT won't have any real effect, because you have to go
> all the way through with the ORDER BY anyway.
>
> On Wed, Jan 11, 2006 at 08:55:32PM +0100, Bendik Rognlien Johansen  
> wrote:
>> Yes,  the rowcount estimates are real, however, it has been a long
>> time since the last VACUUM FULL (there is never a good time).
>>
>> I have clustered the tables, reindexed, analyzed, vacuumed and the
>> plan now looks like this:
>>
>>
>> no_people=# explain SELECT r.id AS r_id, r.firstname || ' ' ||
>> r.lastname AS r_name, ad.id AS ad_id, ad.type AS ad_type, ad.address
>> AS ad_address, ad.postalcode AS ad_postalcode, ad.postalsite AS
>> ad_postalsite, ad.priority AS ad_priority, ad.position[0] AS ad_lat,
>> ad.position[1] AS ad_lon, ad.uncertainty AS ad_uncertainty, ad.extra
>> AS ad_extra, ad.deleted AS ad_deleted, co.id AS co_id, co.type AS
>> co_type, co.value AS co_value, co.description AS co_description,
>> co.priority AS co_priority, co.visible AS co_visible, co.searchable
>> AS co_searchable, co.deleted AS co_deleted FROM people r LEFT OUTER
>> JOIN addresses ad ON(r.id = ad.record) LEFT OUTER JOIN contacts co ON
>> (r.id = co.record) WHERE NOT r.deleted AND  r.original IS NULL ORDER
>> BY r.id;
>>                                                         QUERY PLAN
>> --------------------------------------------------------------------- 
>> ---
>> --------------------------------------------------
>> Sort  (cost=182866.49..182943.12 rows=30655 width=587)
>>    Sort Key: r.id
>>    ->  Nested Loop Left Join  (cost=0.00..170552.10 rows=30655
>> width=587)
>>          ->  Nested Loop Left Join  (cost=0.00..75054.96 rows=26325
>> width=160)
>>                ->  Index Scan using people_deleted_original_is_null
>> on people r  (cost=0.00..1045.47 rows=23861 width=27)
>>                      Filter: ((NOT deleted) AND (original IS NULL))
>>                ->  Index Scan using addresses_record_idx on
>> addresses ad  (cost=0.00..3.05 rows=4 width=137)
>>                      Index Cond: ("outer".id = ad.record)
>>          ->  Index Scan using contacts_record_idx on contacts co
>> (cost=0.00..3.32 rows=24 width=431)
>>                Index Cond: ("outer".id = co.record)
>> (10 rows)
>>
>>
>>
>>
>>
>>
>> Looks faster, but still very slow. I added limit 1000 and it has been
>> running for about 25 minutes now with no output. top shows:
>>
>>
>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>> 29994 postgres  18   0 95768  78m  68m R 17.0  7.7   0:53.27  
>> postmaster
>>
>>
>>
>> which is unusual, I usually get 99.9 %cpu for just about any query,
>> which leads me to believe this is disk related.
>>
>>
>>
>> postgresql.conf:
>> shared_buffers = 8192
>> work_mem = 8192
>> maintenance_work_mem = 524288
>>
>>
>>
>>
>> Hardware 2x2.8GHz cpu
>> 1GB ram
>>
>> Could this be an issue related to lack of VACUUM FULL? The tables get
>> a lot of updates.
>>
>>
>> Thank you very much so far!
>>
>>
>>
>>
>> On Jan 11, 2006, at 4:45 PM, Tom Lane wrote:
>>
>>> Bendik Rognlien Johansen <bendik.johansen@gmail.com> writes:
>>>> Has anyone got any tips for speeding up this query? It currently
>>>> takes hours to start.
>>>
>>> Are the rowcount estimates close to reality?  The plan doesn't look
>>> unreasonable to me if they are.  It might help to increase work_mem
>>> to ensure that the hash tables don't spill to disk.
>>>
>>> Indexes:
>>>     "people_original_is_null" btree (original) WHERE original IS  
>>> NULL
>>>
>>> This index seems poorly designed: the actual index entries are dead
>>> weight since all of them are necessarily NULL.  You might as well  
>>> make
>>> the index carry something that you frequently test in conjunction  
>>> with
>>> "original IS NULL".  For instance, if this particular query is a
>>> common
>>> case, you could replace this index with
>>>
>>> CREATE INDEX people_deleted_original_is_null ON people(deleted)
>>>  WHERE original IS NULL;
>>>
>>> This index is still perfectly usable for queries that only say
>>> "original
>>> IS NULL", but it can also filter out rows with the wrong value of
>>> deleted.  Now, if there are hardly any rows with deleted = true,  
>>> maybe
>>> this won't help much for your problem.  But in any case you ought to
>>> consider whether you can make the index entries do something useful.
>>>
>>> 			regards, tom lane
>>
>>
>> ---------------------------(end of  
>> broadcast)---------------------------
>> TIP 5: don't forget to increase your free space map settings
>>
>
> -- 
> Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
> Pervasive Software      http://pervasive.com    work: 512-231-6117
> vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461


From pgsql-performance-owner@postgresql.org  Wed Jan 11 18:05:22 2006
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From: "Dave Dutcher" <dave@tridecap.com>
To: <pgsql-performance@postgresql.org>
Subject: Showing Column Statistics Number
Date: Wed, 11 Jan 2006 16:05:18 -0600
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Hi,
 
I've looked around through the docs, but can't seem to find an answer to
this.  If I change a column's statistics with "Alter table alter column
set statistics n", is there a way I can later go back and see what the
number is for that column?  I want to be able to tell which columns I've
changed the statistics on, and which ones I haven't.
 
Thanks,
 
Dave

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<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Hi,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>I&#8217;ve looked around through the docs, but =
can&#8217;t
seem to find an answer to this.<span style=3D'mso-spacerun:yes'>&nbsp; =
</span>If
I change a column&#8217;s statistics with &#8220;Alter table alter =
column set
statistics n&#8221;, is there a way I can later go back and see what the =
number
is for that column?<span style=3D'mso-spacerun:yes'>&nbsp; </span>I want =
to be
able to tell which columns I&#8217;ve changed the statistics on, and =
which ones
I haven&#8217;t.<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Thanks,<o:p></o:p></span></font></p>

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<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
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From pgsql-performance-owner@postgresql.org  Wed Jan 11 18:21:44 2006
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From: Michael Fuhr <mike@fuhr.org>
To: Dave Dutcher <dave@tridecap.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Showing Column Statistics Number
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On Wed, Jan 11, 2006 at 04:05:18PM -0600, Dave Dutcher wrote:
> I've looked around through the docs, but can't seem to find an answer to
> this.  If I change a column's statistics with "Alter table alter column
> set statistics n", is there a way I can later go back and see what the
> number is for that column?  I want to be able to tell which columns I've
> changed the statistics on, and which ones I haven't.

pg_attribute.attstattarget

http://www.postgresql.org/docs/8.1/interactive/catalog-pg-attribute.html

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 18:29:02 2006
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Subject: Extremely irregular query performance
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Hi,

I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's)
with 4Gb of RAM. I have recently noticed that the performance of
some more complex queries is extremely variable and irregular.
For example, I currently have a query that returns a small number 
of rows (5) by joining a dozen of tables. Below are the running times
obtained by repeatedly lauching this query in psql (nothing else
was running on the server at that time):

Time: 424.848 ms
Time: 1615.143 ms
Time: 15036.475 ms
Time: 83471.683 ms
Time: 163.224 ms
Time: 2454.939 ms
Time: 188.093 ms
Time: 158.071 ms
Time: 192.431 ms
Time: 195.076 ms
Time: 635.739 ms
Time: 164549.902 ms

As you can see, the performance is most of the time pretty good (less
than 1 second), but every fourth of fifth time I launch the query
the server seems to go into orbit. For the longer running times,
I can see from 'top' that the server process uses almost 100% of
a CPU.

This is rather worrisome, as I cannot be confident of the overall performance
of my application with so much variance in query response times.

I suspect a configuration problem related to the cache mechanism 
(shared_buffers? effective_cache_size?), but to be honest I do not know 
where to start to diagnose it. I also noticed that the query plan
can vary when the same query is launched two times in a row (with
no other changes to the DB in between). Is there a random aspect to
the query optimizer that could explain some of the observed variance
in performance ?

Any help would be greatly appreciated.

Thanks in advance,

J-P




From pgsql-performance-owner@postgresql.org  Wed Jan 11 18:38:44 2006
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Date: Wed, 11 Jan 2006 14:38:42 -0800
From: Burak Seydioglu <buraks78@gmail.com>
To: pgsql-performance@postgresql.org
Subject: indexes on primary and foreign keys
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I do a load of sql joins using primary and foreign keys. What i would like
to know if PostgreSQL creates indexes on these columns automatically (in
addition to using them to maintain referential integrity) or do I have to
create an index manually on these columns as indicated below?

CREATE TABLE cities (
  city_id integer primary key,
  city_name varchar(50)
);

CREATE INDEX city_id_index ON cities(city_id);

Thanks for any insight.

Burak

------=_Part_11166_32945758.1137019122582
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

I do a load of sql joins using primary and foreign keys. What i would
like to know if PostgreSQL creates indexes on these columns
automatically (in addition to using them to maintain referential
integrity) or do I have to create an index manually on these columns as
indicated below?<br>
<br>
<pre style=3D"font-family: arial,sans-serif;">CREATE TABLE cities (<br>  ci=
ty_id integer primary key,<br>  city_name varchar(50)<br>);<br><br>CREATE I=
NDEX city_id_index ON cities(city_id);<br><br>Thanks for any insight.<br>
<br>Burak<br></pre>
<br>


------=_Part_11166_32945758.1137019122582--

From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:03:08 2006
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cc: pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance 
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	<jean-philippe.cote@crt.umontreal.ca>
	message dated "Wed, 11 Jan 2006 17:37:24 -0500"
Date: Wed, 11 Jan 2006 18:03:05 -0500
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=?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's)
> with 4Gb of RAM. I have recently noticed that the performance of
> some more complex queries is extremely variable and irregular.
> For example, I currently have a query that returns a small number 
> of rows (5) by joining a dozen of tables.

A dozen tables?  You're exceeding the geqo_threshold and getting a plan
that has some randomness in it.  You could either increase
geqo_threshold if you can stand the extra planning time, or try
increasing geqo_effort to get it to search a little harder and hopefully
find a passable plan more often.  See

http://www.postgresql.org/docs/8.1/static/geqo.html
http://www.postgresql.org/docs/8.1/static/runtime-config-query.html#RUNTIME-CONFIG-QUERY-GEQO

I'm kinda surprised that you don't get better results with the default
settings.  We could tinker some more with the defaults, if you can
provide evidence about better values ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:06:34 2006
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To: Burak Seydioglu <buraks78@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: indexes on primary and foreign keys 
In-reply-to: <1b8a973c0601111438m3e0b1cc0hf9c387a4a1d6791d@mail.gmail.com> 
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	message dated "Wed, 11 Jan 2006 14:38:42 -0800"
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Burak Seydioglu <buraks78@gmail.com> writes:
> I do a load of sql joins using primary and foreign keys. What i would like
> to know if PostgreSQL creates indexes on these columns automatically (in
> addition to using them to maintain referential integrity) or do I have to
> create an index manually on these columns as indicated below?

Indexes are only automatically created where needed to enforce a UNIQUE
constraint.  That includes primary keys, but not foreign keys.

Note that you only really need an index on the referencing (non-unique)
side of a foreign key if you are worried about performance of DELETEs
or key changes on the referenced table.  If you seldom or never do that,
you might want to dispense with the index.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:22:02 2006
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From: Michael Fuhr <mike@fuhr.org>
To: Burak Seydioglu <buraks78@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: indexes on primary and foreign keys
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On Wed, Jan 11, 2006 at 02:38:42PM -0800, Burak Seydioglu wrote:
> I do a load of sql joins using primary and foreign keys. What i would like
> to know if PostgreSQL creates indexes on these columns automatically (in
> addition to using them to maintain referential integrity) or do I have to
> create an index manually on these columns as indicated below?
> 
> CREATE TABLE cities (
>   city_id integer primary key,
>   city_name varchar(50)
> );
> 
> CREATE INDEX city_id_index ON cities(city_id);

PostgreSQL automatically creates indexes on primary keys.  If you run
the above CREATE TABLE statement in psql you should see a message to
that effect:

NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "cities_pkey" for table "cities"

If you look at the table definition you should see the primary
key's index:

test=> \d cities
             Table "public.cities"
  Column   |         Type          | Modifiers 
-----------+-----------------------+-----------
 city_id   | integer               | not null
 city_name | character varying(50) | 
Indexes:
    "cities_pkey" PRIMARY KEY, btree (city_id)

So you don't need to create another index on cities.city_id.  However,
PostgreSQL doesn't automatically create an index on the referring
column of a foreign key constraint, so if you have another table like

CREATE TABLE districts (
  district_id    integer PRIMARY KEY,
  district_name  varchar(50),
  city_id        integer REFERENCES cities
);

then you won't automatically get an index on districts.city_id.
It's generally a good idea to create one; failure to do so can cause
deletes and updates on the referred-to table (cities) to be slow
because referential integrity checks would have to do sequential
scans on the referring table (districts).  Indeed, performance
problems for exactly this reason occasionally come up in the mailing
lists.

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:29:17 2006
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	11 Jan 2006 17:29:14 -0600
Subject: Re: Extremely irregular query performance
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Jean-Philippe =?ISO-8859-1?Q?C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>
Cc: pgsql-performance@postgresql.org
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On Wed, 2006-01-11 at 16:37, Jean-Philippe C=C3=B4t=C3=A9 wrote:
> Hi,
>=20
> I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's)
> with 4Gb of RAM. I have recently noticed that the performance of
> some more complex queries is extremely variable and irregular.
> For example, I currently have a query that returns a small number=20
> of rows (5) by joining a dozen of tables. Below are the running times
> obtained by repeatedly lauching this query in psql (nothing else
> was running on the server at that time):
>=20
> Time: 424.848 ms
> Time: 1615.143 ms
> Time: 15036.475 ms
> Time: 83471.683 ms
> Time: 163.224 ms
> Time: 2454.939 ms
> Time: 188.093 ms
> Time: 158.071 ms
> Time: 192.431 ms
> Time: 195.076 ms
> Time: 635.739 ms
> Time: 164549.902 ms
>=20
> As you can see, the performance is most of the time pretty good (less
> than 1 second), but every fourth of fifth time I launch the query
> the server seems to go into orbit. For the longer running times,
> I can see from 'top' that the server process uses almost 100% of
> a CPU.

As mentioned earlier, it could be you're exceeding the GEQO threshold.

It could also be that you are doing just enough else at the time, and
have your shared buffers or sort mem high enough that you're initiating
a swap storm.

Mind posting all the parts of your postgresql.conf file you've changed
from the default?

From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:41:50 2006
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To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: <pgsql-performance@postgresql.org>
Subject: Re: Extremely irregular query performance 
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Thanks a lot for this info, I was indeed exceeding the genetic
optimizer's threshold.  Now that it is turned off, I get
a very stable response time of 435ms (more or less 5ms) for
the same query. It is about three times slower than the best
I got with the genetic optimizer on, but the overall average
is much lower.

I'll also try to play with the geqo parameters and see if things
improve.

Thanks again,

J-P


-----Original Message-----
From: pgsql-performance-owner@postgresql.org =
[mailto:pgsql-performance-owner@postgresql.org] On Behalf Of Tom Lane
Sent: January 11, 2006 6:03 PM
To: Jean-Philippe C=F4t=E9
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Extremely irregular query performance=20

=3D?iso-8859-1?Q?Jean-Philippe_C=3DF4t=3DE9?=3D =
<jean-philippe.cote@crt.umontreal.ca> writes:
> I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's)
> with 4Gb of RAM. I have recently noticed that the performance of
> some more complex queries is extremely variable and irregular.
> For example, I currently have a query that returns a small number=20
> of rows (5) by joining a dozen of tables.

A dozen tables?  You're exceeding the geqo_threshold and getting a plan
that has some randomness in it.  You could either increase
geqo_threshold if you can stand the extra planning time, or try
increasing geqo_effort to get it to search a little harder and hopefully
find a passable plan more often.  See

http://www.postgresql.org/docs/8.1/static/geqo.html
http://www.postgresql.org/docs/8.1/static/runtime-config-query.html#RUNTI=
ME-CONFIG-QUERY-GEQO

I'm kinda surprised that you don't get better results with the default
settings.  We could tinker some more with the defaults, if you can
provide evidence about better values ...

			regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match


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	11 Jan 2006 15:50:44 -0800
Subject: Re: Extremely irregular query performance
From: Mark Lewis <mark.lewis@mir3.com>
To: Jean-Philippe =?ISO-8859-1?Q?C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>
Cc: pgsql-performance@postgresql.org
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Date: Wed, 11 Jan 2006 15:50:43 -0800
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If this is a query that will be executed more than once, you can also
avoid incurring the planning overhead multiple times by using PREPARE.

-- Mark Lewis

On Wed, 2006-01-11 at 18:50 -0500, Jean-Philippe C=C3=B4t=C3=A9 wrote:
> Thanks a lot for this info, I was indeed exceeding the genetic
> optimizer's threshold.  Now that it is turned off, I get
> a very stable response time of 435ms (more or less 5ms) for
> the same query. It is about three times slower than the best
> I got with the genetic optimizer on, but the overall average
> is much lower.
>=20
> I'll also try to play with the geqo parameters and see if things
> improve.
>=20
> Thanks again,
>=20
> J-P


From pgsql-performance-owner@postgresql.org  Wed Jan 11 19:52:41 2006
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Date: Wed, 11 Jan 2006 15:52:40 -0800
From: Burak Seydioglu <buraks78@gmail.com>
To: Michael Fuhr <mike@fuhr.org>
Subject: Re: indexes on primary and foreign keys
Cc: pgsql-performance@postgresql.org
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How about the performance effect on SELECT statements joining multiple
tables (LEFT JOINS)?

I have been reading all day and here is an excerpt from one article that is
located at http://pgsql.designmagick.com/tutorial.php?id=3D19&pid=3D28

[quote]

The best reason to use an index is for joining multiple tables
together in a single query. When two tables are joined, a record
that exists in both tables needs to be used to link them together. If
possible, the column in both tables should be indexed.

[/quote]

Regarding similar posts, I tried to search the archives but for some reason
the search utility is not functioning.
http://search.postgresql.org/archives.search?cs=3Dutf-8&fm=3Don&st=3D20&dt=
=3Dback&q=3Dindex

Thank you very much for your help.

Burak


On 1/11/06, Michael Fuhr <mike@fuhr.org> wrote:
>
> On Wed, Jan 11, 2006 at 02:38:42PM -0800, Burak Seydioglu wrote:
> > I do a load of sql joins using primary and foreign keys. What i would
> like
> > to know if PostgreSQL creates indexes on these columns automatically (i=
n
> > addition to using them to maintain referential integrity) or do I have
> to
> > create an index manually on these columns as indicated below?
> >
> > CREATE TABLE cities (
> >   city_id integer primary key,
> >   city_name varchar(50)
> > );
> >
> > CREATE INDEX city_id_index ON cities(city_id);
>
> PostgreSQL automatically creates indexes on primary keys.  If you run
> the above CREATE TABLE statement in psql you should see a message to
> that effect:
>
> NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index
> "cities_pkey" for table "cities"
>
> If you look at the table definition you should see the primary
> key's index:
>
> test=3D> \d cities
>              Table "public.cities"
>   Column   |         Type          | Modifiers
> -----------+-----------------------+-----------
> city_id   | integer               | not null
> city_name | character varying(50) |
> Indexes:
>     "cities_pkey" PRIMARY KEY, btree (city_id)
>
> So you don't need to create another index on cities.city_id.  However,
> PostgreSQL doesn't automatically create an index on the referring
> column of a foreign key constraint, so if you have another table like
>
> CREATE TABLE districts (
>   district_id    integer PRIMARY KEY,
>   district_name  varchar(50),
>   city_id        integer REFERENCES cities
> );
>
> then you won't automatically get an index on districts.city_id.
> It's generally a good idea to create one; failure to do so can cause
> deletes and updates on the referred-to table (cities) to be slow
> because referential integrity checks would have to do sequential
> scans on the referring table (districts).  Indeed, performance
> problems for exactly this reason occasionally come up in the mailing
> lists.
>
> --
> Michael Fuhr
>

------=_Part_11920_17810882.1137023560071
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How about the performance effect on SELECT statements joining multiple tabl=
es (LEFT JOINS)?<br>
<br>
I have been reading all day and here is an excerpt from one article
that is located at
<a href=3D"http://pgsql.designmagick.com/tutorial.php?id=3D19&amp;pid=3D28"=
>http://pgsql.designmagick.com/tutorial.php?id=3D19&amp;pid=3D28</a><br>
<br>
[quote]<br>
<pre style=3D"font-family: arial,sans-serif;">The best reason to use an ind=
ex is for joining multiple tables together in a single query. When two tabl=
es are joined, a record<br>that exists in both tables needs to be used to l=
ink them together. If possible, the column in both tables should be indexed=
.
</pre>
[/quote]<br>
<br>
Regarding similar posts, I tried to search the archives but for some reason=
 the search utility is not functioning. <br>
<a href=3D"http://search.postgresql.org/archives.search?cs=3Dutf-8&amp;fm=
=3Don&amp;st=3D20&amp;dt=3Dback&amp;q=3Dindex">http://search.postgresql.org=
/archives.search?cs=3Dutf-8&amp;fm=3Don&amp;st=3D20&amp;dt=3Dback&amp;q=3Di=
ndex</a><br>
<br>
Thank you very much for your help.<br>
<br>
Burak<br>
<br><br><div><span class=3D"gmail_quote">On 1/11/06, <b class=3D"gmail_send=
ername">Michael Fuhr</b> &lt;<a href=3D"mailto:mike@fuhr.org">mike@fuhr.org=
</a>&gt; wrote:</span><blockquote class=3D"gmail_quote" style=3D"border-lef=
t: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1=
ex;">
On Wed, Jan 11, 2006 at 02:38:42PM -0800, Burak Seydioglu wrote:<br>&gt; I =
do a load of sql joins using primary and foreign keys. What i would like<br=
>&gt; to know if PostgreSQL creates indexes on these columns automatically =
(in
<br>&gt; addition to using them to maintain referential integrity) or do I =
have to<br>&gt; create an index manually on these columns as indicated belo=
w?<br>&gt;<br>&gt; CREATE TABLE cities (<br>&gt;&nbsp;&nbsp; city_id intege=
r primary key,
<br>&gt;&nbsp;&nbsp; city_name varchar(50)<br>&gt; );<br>&gt;<br>&gt; CREAT=
E INDEX city_id_index ON cities(city_id);<br><br>PostgreSQL automatically c=
reates indexes on primary keys.&nbsp;&nbsp;If you run<br>the above CREATE T=
ABLE statement in psql you should see a message to
<br>that effect:<br><br>NOTICE:&nbsp;&nbsp;CREATE TABLE / PRIMARY KEY will =
create implicit index &quot;cities_pkey&quot; for table &quot;cities&quot;<=
br><br>If you look at the table definition you should see the primary<br>ke=
y's index:
<br><br>test=3D&gt; \d cities<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Table &quot;public.cities&quot;<br>&nbsp;&nb=
sp;Column&nbsp;&nbsp;
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
Type&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|
Modifiers<br>-----------+-----------------------+-----------<br> city_id&nb=
sp;&nbsp; | integer&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp; | not null<br> city_name | character varying(5=
0) |<br>Indexes:<br>&nbsp;&nbsp;&nbsp;&nbsp;&quot;cities_pkey&quot; PRIMARY=
 KEY, btree (city_id)
<br><br>So you don't need to create another index on cities.city_id.&nbsp;&=
nbsp;However,<br>PostgreSQL doesn't automatically create an index on the re=
ferring<br>column of a foreign key constraint, so if you have another table=
 like<br>
<br>CREATE TABLE districts (<br>&nbsp;&nbsp;district_id&nbsp;&nbsp;&nbsp;&n=
bsp;integer PRIMARY KEY,<br>&nbsp;&nbsp;district_name&nbsp;&nbsp;varchar(50=
),<br>&nbsp;&nbsp;city_id&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;in=
teger REFERENCES cities<br>);<br><br>then you won't automatically get an in=
dex on districts.city_id
.<br>It's generally a good idea to create one; failure to do so can cause<b=
r>deletes and updates on the referred-to table (cities) to be slow<br>becau=
se referential integrity checks would have to do sequential<br>scans on the=
 referring table (districts).&nbsp;&nbsp;Indeed, performance
<br>problems for exactly this reason occasionally come up in the mailing<br=
>lists.<br><br>--<br>Michael Fuhr<br></blockquote></div><br>

------=_Part_11920_17810882.1137023560071--

From pgsql-performance-owner@postgresql.org  Wed Jan 11 20:32:31 2006
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Date: Thu, 12 Jan 2006 01:32:10 +0100
From: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
  <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
  <title></title>
</head>
<body bgcolor="#ffffff" text="#000000">
<pre style="margin: 0em;">Hi,
<font face="Arial, Helvetica, sans-serif">
I'm working on a project, whose implementation deals with PostgreSQL. A brief description of our application is given  below.</font>

I'm running version 8.0 on a dedicated  server 1Gb of RAM. 
my database isn't complex, it contains just 2 simple tables.
<tt>
CREATE TABLE cookies (
    domain varchar(50) NOT NULL,
    path varchar(50) NOT NULL,
    name varchar(50) NOT NULL,
    principalid varchar(50) NOT NULL,
    host text NOT NULL,
    value text NOT NULL,
    secure bool NOT NULL,
    timestamp timestamp with time zone NOT NULL DEFAULT 
CURRENT_TIMESTAMP+TIME '04:00:00',
    PRIMARY KEY  (domain,path,name,principalid)
)

CREATE TABLE liberty (
    principalid varchar(50) NOT NULL,
    requestid varchar(50) NOT NULL,
    spassertionurl text NOT NULL,
    libertyversion  varchar(50) NOT NULL,
    relaystate  varchar(50) NOT NULL,
    PRIMARY KEY  (principalid)
)

</tt>I'm developping an application that uses the libpqxx to execute 
psql queries on the database and have to execute 500 requests at the same time.

<tt>
UPDATE cookies SET host='ping.icap-elios.com', value= '54E5B5491F27C0177083795F2E09162D', secure=FALSE, 
timestamp=CURRENT_TIMESTAMP+INTERVAL '14400 SECOND' WHERE 
domain='ping.icap-elios.com' AND path='/tfs' AND principalid='192.168.8.219' AND 
name='jsessionid'</tt>

<tt>SELECT path, upper(name) AS name, value FROM cookies  WHERE timestamp&lt;CURRENT_TIMESTAMP AND principalid='192.168.8.219' AND 
secure=FALSE AND (domain='ping.icap-elios.com' OR domain='.icap-elios.com')</tt>

I have to notify that the performance of is extremely variable and irregular.
I can also see that the server process uses almost 100% of
a CPU.

I'm using the default configuration file, and i m asking if i have to change some paramters to have a good performance.

Any help would be greatly appreciated.

Thanks,
</pre>
</body>
</html>


From pgsql-performance-owner@postgresql.org  Wed Jan 11 21:00:56 2006
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Date: Thu, 12 Jan 2006 08:36:19 +0800
To: pgsql-performance@postgresql.org
From: K C Lau <kclau60@netvigator.com>
Subject: Re: indexes on primary and foreign keys
In-Reply-To: <20060111232157.GA88829@winnie.fuhr.org>
References: <1b8a973c0601111438m3e0b1cc0hf9c387a4a1d6791d@mail.gmail.com>
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At 07:21 06/01/12, Michael Fuhr wrote:
>On Wed, Jan 11, 2006 at 02:38:42PM -0800, Burak Seydioglu wrote:
> > I do a load of sql joins using primary and foreign keys. What i would like
> > to know if PostgreSQL creates indexes on these columns automatically (in
> > addition to using them to maintain referential integrity) or do I have to
> > create an index manually on these columns as indicated below?
> >
> > CREATE TABLE cities (
> >   city_id integer primary key,
> >   city_name varchar(50)
> > );
> >
> > CREATE INDEX city_id_index ON cities(city_id);
>
>PostgreSQL automatically creates indexes on primary keys.  If you run
>the above CREATE TABLE statement in psql you should see a message to
>that effect:
>
>NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index 
>"cities_pkey" for table "cities"

Is there a way to suppress this notice when I create tables in a script?

Best regards,
KC.



From pgsql-performance-owner@postgresql.org  Wed Jan 11 20:41:29 2006
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Hi,

I've got a set-returning function,  defined as STABLE, that I reference twice 
within a single query, yet appears to be evaluated via two seperate function 
scans.  I created a simple query that calls the function below and joins the 
results to itself (Note:  in case you wonder why I'd do such a query, it's 
not my actual query, which is much more complex.  I just created this simple 
query to try to test out the 'stable' behavior).


select proname,provolatile from pg_proc where proname = 'get_tran_filesize';
             proname        | provolatile
----------------------------+-------------
 get_tran_filesize          | s
(1 row)


explain analyze
select * from 
 get_tran_filesize('2005-12-11 00:00:00-08','2006-01-11 
15:58:33-08','{228226,228222,228210}');

                                                              QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
 Function Scan on get_tran_filesize  (cost=0.00..12.50 rows=1000 width=40) 
(actual time=49.522..49.524 rows=3 loops=1)
 Total runtime: 49.550 ms
(2 rows)


explain analyze
select * from 
 get_tran_filesize('2005-12-11 00:00:00-08','2006-01-11 
15:58:33-08','{228226,228222,228210}') gt,
 get_tran_filesize('2005-12-11 00:00:00-08','2006-01-11 
15:58:33-08','{228226,228222,228210}') gt2
where gt.tran_id = gt2.tran_id;

                                                                      QUERY 
PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------
 Merge Join  (cost=124.66..204.66 rows=5000 width=80) (actual 
time=83.027..83.040 rows=3 loops=1)
   Merge Cond: ("outer".tran_id = "inner".tran_id)
   ->  Sort  (cost=62.33..64.83 rows=1000 width=40) (actual 
time=40.250..40.251 rows=3 loops=1)
         Sort Key: gt.tran_id
         ->  Function Scan on get_tran_filesize gt  (cost=0.00..12.50 
rows=1000 width=40) (actual time=40.237..40.237 rows=3 loops=1)
   ->  Sort  (cost=62.33..64.83 rows=1000 width=40) (actual 
time=42.765..42.767 rows=3 loops=1)
         Sort Key: gt2.tran_id
         ->  Function Scan on get_tran_filesize gt2  (cost=0.00..12.50 
rows=1000 width=40) (actual time=42.748..42.751 rows=3 loops=1)
 Total runtime: 83.112 ms
(9 rows)


If I do get this working, then my question is, if I reference this function 
within a single query, but within seperate subqueries within the query, will 
it be re-evaluated each time, or just once.  Basically, I'm not clear on the 
definition of "surrounding query" in the following exerpt from the Postgreql 
documentation:

A STABLE function cannot modify the database and is guaranteed to return the 
same results given the same arguments for all calls within a single
surrounding query.

Thanks,

Mark

From pgsql-performance-owner@postgresql.org  Wed Jan 11 20:48:37 2006
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Subject: Re: NOT LIKE much faster than LIKE?
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matteo Beccati <php@beccati.com>, Andrea Arcangeli <andrea@cpushare.com>,
	pgsql-performance@postgresql.org
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On Tue, 2006-01-10 at 17:21 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > I think its OK to use the MCV, but I have a problem with the current
> > heuristics: they only work for randomly generated strings, since the
> > selectivity goes down geometrically with length.
> 
> We could certainly use a less aggressive curve for that.  You got a
> specific proposal?

non-left anchored LIKE is most likely going to be used with
unstructured, variable length data - else we might use SUBSTRING
instead. My proposal would be to assume that LIKE is acting on human
language text data.

I considered this a while back, but wrote it off in favour of dynamic
sampling - but it's worth discussing this to see whether we can improve
on things without that.

Here's one of the links I reviewed previously:
http://www.ling.lu.se/persons/Joost/Texts/studling.pdf
Sigurd et al [2004]

This shows word frequency distribution peaks at 3 letter/2 phoneme
words, then tails off exponentially after that.

Clearly when search string > 3 then the selectivity must tail off
exponentially also, since we couldn't find words shorter than the search
string itself. The search string might be a phrase, but it seems
reasonable to assume that phrases also drop off in frequency according
to length. It is difficult to decide what to do at len=2 or len=3, and I
would be open to various thoughts, but would default to keeping
like_selectivity as it is now.

Sigurd et al show that word length tails off at 0.7^Len beyond Len=3, so
selectivity FIXED_CHAR_SEL should not be more than 0.7, but I see no
evidence for it being as low as 0.2 (from the published results).  For
simplicity, where Len > 3, I would make the tail off occur with factor
0.5, rather than 0.2.

We could see a few more changes from those results, but curbing the
aggressive tail off would be a simple and easy act.

Best Regards, Simon Riggs


From pgsql-performance-owner@postgresql.org  Wed Jan 11 21:27:07 2006
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From: Michael Glaesemann <grzm@myrealbox.com>
Subject: Re: indexes on primary and foreign keys
Date: Thu, 12 Jan 2006 10:26:58 +0900
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On Jan 12, 2006, at 9:36 , K C Lau wrote:

>> NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index  
>> "cities_pkey" for table "cities"
>
> Is there a way to suppress this notice when I create tables in a  
> script?

Set[1] your log_min_messages to WARNING or higher[2].

[1](http://www.postgresql.org/docs/current/interactive/sql-set.html)
[2](http://www.postgresql.org/docs/current/interactive/runtime-config- 
logging.html#RUNTIME-CONFIG-LOGGING-WHEN)

Michael Glaesemann
grzm myrealbox com




From pgsql-performance-owner@postgresql.org  Wed Jan 11 21:41:08 2006
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Subject: Re: indexes on primary and foreign keys
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On Thu, Jan 12, 2006 at 10:26:58AM +0900, Michael Glaesemann wrote:
> On Jan 12, 2006, at 9:36 , K C Lau wrote:
> >>NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index  
> >>"cities_pkey" for table "cities"
> >
> >Is there a way to suppress this notice when I create tables in a  
> >script?
> 
> Set[1] your log_min_messages to WARNING or higher[2].

Or client_min_messages, depending on where you don't want to see
the notice.

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 11 23:23:57 2006
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To: =?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>
cc: pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance 
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	<jean-philippe.cote@crt.umontreal.ca>
	message dated "Wed, 11 Jan 2006 18:50:12 -0500"
Date: Wed, 11 Jan 2006 22:23:55 -0500
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=?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> Thanks a lot for this info, I was indeed exceeding the genetic
> optimizer's threshold.  Now that it is turned off, I get
> a very stable response time of 435ms (more or less 5ms) for
> the same query. It is about three times slower than the best
> I got with the genetic optimizer on, but the overall average
> is much lower.

Hmm.  It would be interesting to use EXPLAIN ANALYZE to confirm that the
plan found this way is the same as the best plan found by GEQO, and
the extra couple hundred msec is the price you pay for the exhaustive
plan search.  If GEQO is managing to find a plan better than the regular
planner then we need to look into why ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 11 23:49:23 2006
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Date: Thu, 12 Jan 2006 11:49:16 +0800
To: pgsql-performance@postgresql.org
From: K C Lau <kclau60@netvigator.com>
Subject: Re: indexes on primary and foreign keys
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At 09:26 06/01/12, you wrote:

>On Jan 12, 2006, at 9:36 , K C Lau wrote:
>
>>>NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index
>>>"cities_pkey" for table "cities"
>>
>>Is there a way to suppress this notice when I create tables in a
>>script?
>
>Set[1] your log_min_messages to WARNING or higher[2].
>
>[1](http://www.postgresql.org/docs/current/interactive/sql-set.html)
>[2](http://www.postgresql.org/docs/current/interactive/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHEN)
>
>Michael Glaesemann
>grzm myrealbox com

Thanks. The side effect is that it would suppress other notices which might 
be useful.

I was looking for a way to suppress the notice within the CREATE TABLE 
statement but could not.
I noticed that when I specify a constraint name for the primary key, it 
would create an implicit index with the constraint name. So may be if the 
optional constraint name is specified by the user, then the notice can be 
suppressed. Indeed the manual already says that the index will be 
automatically created.

BTW, there's an extra space in link[2] above which I have removed.

Best regards,
KC. 


From pgsql-performance-owner@postgresql.org  Thu Jan 12 00:21:01 2006
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When grilled further on (Wed, 11 Jan 2006 10:33:03 -0500),
Tom Lane <tgl@sss.pgh.pa.us> confessed:

> The planner understands about transitivity of equality, ie given a =3D b
> and b =3D c it can infer a =3D c.  It doesn't do any such thing for
> inequalities though, nor does it deduce f(a) =3D f(b) for arbitrary
> functions f.  The addition Michael suggested requires much more
> understanding of the properties of the functions in your query than
> I think would be reasonable to put into the planner.
>=20

OK.  I think reached a point that I need to re-organize how the data is sto=
red,
maybe ridding myself of the schema and switching entirely to views.  At that
point, I likely could rid myself of the function (unmunge_time) I'm using, =
and
work with times and doy fields.

Thanks,
Rob

--=20
 21:17:00 up 4 days, 13:43,  9 users,  load average: 2.02, 2.18, 2.23
Linux 2.6.12-12-2 #4 SMP Tue Jan 3 19:56:19 MST 2006

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From pgsql-performance-owner@postgresql.org  Thu Jan 12 00:33:28 2006
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To: Mark Liberman <mliberman@mixedsignals.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Stable function being evaluated more than once in a single query 
In-reply-to: <200601111641.20627.mliberman@mixedsignals.com> 
References: <200601111641.20627.mliberman@mixedsignals.com>
Comments: In-reply-to Mark Liberman <mliberman@mixedsignals.com>
	message dated "Wed, 11 Jan 2006 16:41:20 -0800"
Date: Wed, 11 Jan 2006 23:33:23 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Mark Liberman <mliberman@mixedsignals.com> writes:
> I've got a set-returning function,  defined as STABLE, that I reference twice
> within a single query, yet appears to be evaluated via two seperate function 
> scans.

There is no guarantee, express or implied, that this won't be the case.

(Seems like we just discussed this a couple days ago...)

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Thu Jan 12 00:48:25 2006
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To: K C Lau <kclau60@netvigator.com>
cc: pgsql-performance@postgresql.org
Subject: Re: indexes on primary and foreign keys 
In-reply-to: <6.2.1.2.0.20060112103712.0529cdd0@localhost> 
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Comments: In-reply-to K C Lau <kclau60@netvigator.com>
	message dated "Thu, 12 Jan 2006 11:49:16 +0800"
Date: Wed, 11 Jan 2006 23:45:49 -0500
Message-ID: <1092.1137041149@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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K C Lau <kclau60@netvigator.com> writes:
> Thanks. The side effect is that it would suppress other notices which might 
> be useful.

There's been some discussion of subdividing the present "notice"
category into two subclasses, roughly defined as "only novices wouldn't
know this" and "maybe this is interesting".  What's missing at this
point is a concrete proposal as to which existing NOTICE messages should
go into each category.  If you feel like tackling the project, go for it...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Thu Jan 12 05:49:01 2006
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Subject: Re: Extremely irregular query performance
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jean-Philippe =?ISO-8859-1?Q?C=F4t=E9?=
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On Wed, 2006-01-11 at 22:23 -0500, Tom Lane wrote:
> =?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> > Thanks a lot for this info, I was indeed exceeding the genetic
> > optimizer's threshold.  Now that it is turned off, I get
> > a very stable response time of 435ms (more or less 5ms) for
> > the same query. It is about three times slower than the best
> > I got with the genetic optimizer on, but the overall average
> > is much lower.
> 
> Hmm.  It would be interesting to use EXPLAIN ANALYZE to confirm that the
> plan found this way is the same as the best plan found by GEQO, and
> the extra couple hundred msec is the price you pay for the exhaustive
> plan search.  If GEQO is managing to find a plan better than the regular
> planner then we need to look into why ...

It seems worth noting in the EXPLAIN whether GEQO has been used to find
the plan, possibly along with other factors influencing the plan such as
enable_* settings.

Best Regards, Simon Riggs


From pgsql-performance-owner@postgresql.org  Thu Jan 12 08:19:00 2006
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From: =?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com>
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Subject: Throwing unnecessary joins away
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Hi all,

Is PostgreSQL able to throw unnecessary joins?
For example I have two tables, and I join then with their primary keys, say
type of bigint . In this case if I don't reference to one of the
tables anywhere except the join condition, then the join can be eliminated.
Or if I do a "table1 left join table2 (table1.referer=3Dtable2.id)"  (N : 1
relationship), and I don't reference table2 anywhere else, then it is
unnecessary.
Primary key - primary key joins are often generated by O/R mappers. These
generated queries could be optimized even more by not joining if not
necessary.

You may say that I should not write such queries. The truth is that the O/R
mapper is generating queries on views, and it does not use every field ever=
y
time, but even so the query of the view is executed with the same plan by
PostgreSQL, although some joins are unnecessary.

So basically this all is relevant only with views.

Best Regards,
Otto

------=_Part_11612_32089099.1137068338744
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<div>Hi all,</div>
<div>&nbsp;</div>
<div>Is PostgreSQL able to throw unnecessary joins?</div>
<div>For example I have two tables, and I join then with their primary keys=
, say type of bigint&nbsp;. In this case if I don't reference to one of the=
 tables&nbsp;anywhere except the join condition, then&nbsp;the join can be =
eliminated.=20
</div>
<div>Or if I do a &quot;table1 left join table2 (table1.referer=3Dtable2.id=
)&quot;&nbsp; (N : 1 relationship), and I don't reference table2 anywhere e=
lse, then it is unnecessary.</div>
<div>Primary key - primary key joins are often generated by O/R mappers. Th=
ese generated queries could be optimized even more by not joining if not ne=
cessary.</div>
<div>&nbsp;</div>
<div>You may say that I should not write such queries. The truth is that th=
e O/R mapper is generating queries on views, and it does not use every fiel=
d every time, but even so the query of the view is executed&nbsp;with the s=
ame plan by PostgreSQL, although some joins are unnecessary.
</div>
<div>&nbsp;</div>
<div>So basically this all is relevant only with views.</div>
<div>&nbsp;</div>
<div>Best Regards,</div>
<div>Otto</div>

------=_Part_11612_32089099.1137068338744--

From pgsql-performance-owner@postgresql.org  Thu Jan 12 08:34:56 2006
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Date: Thu, 12 Jan 2006 13:35:07 +0100
From: Alessandro Baretta <a.baretta@barettadeit.com>
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Cc: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
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Ott� Havasv�lgyi wrote:
> Hi all,
>  
> Is PostgreSQL able to throw unnecessary joins?
> For example I have two tables, and I join then with their primary keys, 
> say type of bigint . In this case if I don't reference to one of the 
> tables anywhere except the join condition, then the join can be eliminated.
> Or if I do a "table1 left join table2 (table1.referer=table2.id)"  (N : 
> 1 relationship), and I don't reference table2 anywhere else, then it is 
> unnecessary.

It cannot possibly remove "unnecessary joins", simply because the join 
influences whether a tuple in the referenced table gets selected and how many times.

Alex


-- 
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From pgsql-performance-owner@postgresql.org  Thu Jan 12 09:41:29 2006
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From: =?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
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Hi,
As far as I know SQL Server has some similar feature. It does not join
if not necessary, more exactly: if the result would be the same if it
joined the table.
Here is another example:
http://www.ianywhere.com/developer/product_manuals/sqlanywhere/0902/en/html=
/dbugen9/00000468.htm
This would be a fantastic feature.
Best Regards,
Otto


2006/1/12, Alessandro Baretta <a.baretta@barettadeit.com>:
> Ott=F3 Havasv=F6lgyi wrote:
> > Hi all,
> >
> > Is PostgreSQL able to throw unnecessary joins?
> > For example I have two tables, and I join then with their primary keys,
> > say type of bigint . In this case if I don't reference to one of the
> > tables anywhere except the join condition, then the join can be elimina=
ted.
> > Or if I do a "table1 left join table2 (table1.referer=3Dtable2.id)"  (N=
 :
> > 1 relationship), and I don't reference table2 anywhere else, then it is
> > unnecessary.
>
> It cannot possibly remove "unnecessary joins", simply because the join
> influences whether a tuple in the referenced table gets selected and how =
many times.
>
> Alex
>
>
> --
> *********************************************************************
> http://www.barettadeit.com/
> Baretta DE&IT
> A division of Baretta SRL
>
> tel. +39 02 370 111 55
> fax. +39 02 370 111 54
>
> Our technology:
>
> The Application System/Xcaml (AS/Xcaml)
> <http://www.asxcaml.org/>
>
> The FreerP Project
> <http://www.freerp.org/>
>

From pgsql-performance-owner@postgresql.org  Thu Jan 12 10:48:35 2006
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Subject: query slower on 8.1 than 7.3
From: Robert Treat <xzilla@users.sourceforge.net>
To: pgsql-performance@postgresql.org
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Porting app from 7.3 to 8.1, have hit a query that is slower. Everything
is analyzed / vacuumed appropriately. I've managed to pare the query
down into something manageable that still gives me a problem, it looks
like this:

SELECT 
    * 
FROM
    (
        SELECT
            software_download.*
        FROM
            (
                SELECT
                    host_id, max(mtime) as mtime
                FROM   
                    software_download
                    JOIN software_binary USING (software_binary_id)
                WHERE
                    binary_type_id IN (3,5,6) AND bds_status_id not in (6,17,18)
                GROUP BY
                    host_id, software_binary_id
             ) latest_download
             JOIN software_download using (host_id,mtime)
    ) ld
    LEFT JOIN
    (
	SELECT
            entityid, rmsbinaryid, rmsbinaryid as software_binary_id, timestamp as downloaded, ia.host_id
        FROM
            (
		SELECT
                    entityid, rmsbinaryid,max(msgid) as msgid
                FROM
                    msg306u
                WHERE
                    downloadstatus=1
                GROUP BY entityid,rmsbinaryid
            ) a1
            JOIN myapp_app ia on (entityid=myapp_app_id)
            JOIN (
		    SELECT 
			*
                    FROM 
			msg306u
                    WHERE
                        downloadstatus != 0
                  ) a2 USING(entityid,rmsbinaryid,msgid)
     ) aa USING (host_id,software_binary_id)



The problem seems to stem from 8.1's thinking that using a nested loop
left join is a good idea. The 7.3 explain plan looks like this:

 Hash Join  (cost=10703.38..11791.64 rows=1 width=150) (actual time=2550.23..2713.26 rows=475 loops=1)
   Hash Cond: ("outer".host_id = "inner".host_id)
   Join Filter: ("outer".software_binary_id = "inner".rmsbinaryid)
   ->  Merge Join  (cost=1071.80..2160.07 rows=1 width=110) (actual time=93.16..252.12 rows=475 loops=1)
         Merge Cond: ("outer".host_id = "inner".host_id)
         Join Filter: ("inner".mtime = "outer".mtime)
         ->  Index Scan using software_download_host_id on software_download  (cost=0.00..973.16 rows=18513 width=98) (actual time=0.05..119.89 rows=15587 loops=1)
         ->  Sort  (cost=1071.80..1072.81 rows=403 width=20) (actual time=90.82..94.97 rows=7328 loops=1)
               Sort Key: latest_download.host_id
               ->  Subquery Scan latest_download  (cost=1014.00..1054.34 rows=403 width=20) (actual time=85.60..90.12 rows=475 loops=1)
                     ->  Aggregate  (cost=1014.00..1054.34 rows=403 width=20) (actual time=85.59..89.27 rows=475 loops=1)
                           ->  Group  (cost=1014.00..1044.26 rows=4034 width=20) (actual time=85.55..87.61 rows=626 loops=1)
                                 ->  Sort  (cost=1014.00..1024.09 rows=4034 width=20) (actual time=85.54..85.86 rows=626 loops=1)
                                       Sort Key: software_download.host_id, software_download.software_binary_id
                                       ->  Hash Join  (cost=21.64..772.38 rows=4034 width=20) (actual time=1.06..84.14 rows=626 loops=1)
                                             Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
                                             ->  Seq Scan on software_download  (cost=0.00..565.98 rows=17911 width=16) (actual time=0.06..67.26 rows=15364 loops=1)
                                                   Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
                                             ->  Hash  (cost=21.59..21.59 rows=20 width=4) (actual time=0.94..0.94 rows=0 loops=1)
                                                   ->  Seq Scan on software_binary  (cost=0.00..21.59 rows=20 width=4) (actual time=0.32..0.91 rows=23 loops=1)
                                                         Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
   ->  Hash  (cost=9631.57..9631.57 rows=1 width=40) (actual time=2457.04..2457.04 rows=0 loops=1)
         ->  Merge Join  (cost=9495.38..9631.57 rows=1 width=40) (actual time=2345.77..2456.74 rows=240 loops=1)
               Merge Cond: (("outer".rmsbinaryid = "inner".rmsbinaryid) AND ("outer".msgid = "inner".msgid) AND ("outer".entityid = "inner".entityid))
               ->  Sort  (cost=4629.24..4691.15 rows=24761 width=20) (actual time=514.19..539.04 rows=25544 loops=1)
                     Sort Key: msg306u.rmsbinaryid, msg306u.msgid, msg306u.entityid
                     ->  Seq Scan on msg306u  (cost=0.00..2556.22 rows=24761 width=20) (actual time=0.08..228.09 rows=25544 loops=1)
                           Filter: (downloadstatus <> '0'::text)
               ->  Sort  (cost=4866.14..4872.33 rows=2476 width=20) (actual time=1831.55..1831.68 rows=241 loops=1)
                     Sort Key: a1.rmsbinaryid, a1.msgid, a1.entityid
                     ->  Hash Join  (cost=4429.43..4726.56 rows=2476 width=20) (actual time=1724.39..1830.63 rows=325 loops=1)
                           Hash Cond: ("outer".entityid = "inner".myapp_app_id)
                           ->  Subquery Scan a1  (cost=4363.24..4610.85 rows=2476 width=12) (actual time=1714.04..1818.66 rows=325 loops=1)
                                 ->  Aggregate  (cost=4363.24..4610.85 rows=2476 width=12) (actual time=1714.03..1818.08 rows=325 loops=1)
                                       ->  Group  (cost=4363.24..4548.95 rows=24761 width=12) (actual time=1714.01..1796.43 rows=25544 loops=1)
                                             ->  Sort  (cost=4363.24..4425.15 rows=24761 width=12) (actual time=1714.00..1739.34 rows=25544 loops=1)
                                                   Sort Key: entityid, rmsbinaryid
                                                   ->  Seq Scan on msg306u  (cost=0.00..2556.22 rows=24761 width=12) (actual time=0.03..152.94 rows=25544 loops=1)
                                                         Filter: (downloadstatus = '1'::text)
                           ->  Hash  (cost=61.95..61.95 rows=1695 width=8) (actual time=10.25..10.25 rows=0 loops=1)
                                 ->  Seq Scan on myapp_app ia  (cost=0.00..61.95 rows=1695 width=8) (actual time=0.09..5.48 rows=1698 loops=1)
 Total runtime: 2716.84 msec


Compared to the 8.1 plan:

 Nested Loop Left Join  (cost=2610.56..6491.82 rows=1 width=112) (actual time=166.411..4468.322 rows=472 loops=1)
   Join Filter: (("outer".host_id = "inner".host_id) AND ("outer".software_binary_id = "inner".rmsbinaryid))
   ->  Merge Join  (cost=616.56..1495.06 rows=1 width=96) (actual time=47.004..120.085 rows=472 loops=1)
         Merge Cond: ("outer".host_id = "inner".host_id)
         Join Filter: ("inner".mtime = "outer".mtime)
         ->  Index Scan using software_download_host_id on software_download  (cost=0.00..615.92 rows=13416 width=96) (actual time=0.017..35.243 rows=13372 loops=1)
         ->  Sort  (cost=616.56..620.45 rows=1555 width=12) (actual time=46.034..53.978 rows=6407 loops=1)
               Sort Key: latest_download.host_id
               ->  Subquery Scan latest_download  (cost=499.13..534.12 rows=1555 width=12) (actual time=43.137..45.058 rows=472 loops=1)
                     ->  HashAggregate  (cost=499.13..518.57 rows=1555 width=16) (actual time=43.132..43.887 rows=472 loops=1)
                           ->  Hash Join  (cost=5.64..477.57 rows=2875 width=16) (actual time=0.206..41.782 rows=623 loops=1)
                                 Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
                                 ->  Seq Scan on software_download  (cost=0.00..377.78 rows=13080 width=16) (actual time=0.007..23.679 rows=13167 loops=1)
                                       Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
                                 ->  Hash  (cost=5.59..5.59 rows=20 width=4) (actual time=0.155..0.155 rows=22 loops=1)
                                       ->  Seq Scan on software_binary  (cost=0.00..5.59 rows=20 width=4) (actual time=0.011..0.111 rows=22 loops=1)
                                             Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
   ->  Nested Loop  (cost=1994.00..4996.74 rows=1 width=20) (actual time=0.259..8.870 rows=238 loops=472)
         ->  Nested Loop  (cost=1994.00..4992.28 rows=1 width=16) (actual time=0.249..5.851 rows=238 loops=472)
               Join Filter: ("outer".rmsbinaryid = "inner".rmsbinaryid)
               ->  HashAggregate  (cost=1994.00..2001.41 rows=593 width=12) (actual time=0.236..0.942 rows=323 loops=472)
                     ->  Seq Scan on msg306u  (cost=0.00..1797.28 rows=26230 width=12) (actual time=0.009..69.590 rows=25542 loops=1)
                           Filter: (downloadstatus = '1'::text)
               ->  Index Scan using msg306u_entityid_msgid_idx on msg306u  (cost=0.00..5.02 rows=1 width=20) (actual time=0.008..0.010 rows=1 loops=152456)
                     Index Cond: (("outer".entityid = msg306u.entityid) AND ("outer"."?column3?" = msg306u.msgid))
                     Filter: (downloadstatus <> '0'::text)
         ->  Index Scan using myapp_app_pkey on myapp_app ia  (cost=0.00..4.44 rows=1 width=8) (actual time=0.006..0.007 rows=1 loops=112336)
               Index Cond: ("outer".entityid = ia.myapp_app_id)
 Total runtime: 4469.506 ms


What is really tossing me here is I set enable_nestloop = off and got this plan:

 Hash Left Join  (cost=7034.77..7913.29 rows=1 width=112) (actual time=483.840..551.136 rows=472 loops=1)
   Hash Cond: (("outer".host_id = "inner".host_id) AND ("outer".software_binary_id = "inner".rmsbinaryid))
   ->  Merge Join  (cost=616.56..1495.06 rows=1 width=96) (actual
time=46.696..112.434 rows=472 loops=1)
         Merge Cond: ("outer".host_id = "inner".host_id)
         Join Filter: ("inner".mtime = "outer".mtime)
         ->  Index Scan using software_download_host_id on software_download  (cost=0.00..615.92 rows=13416 width=96) (actual time=0.019..30.345 rows=13372 loops=1)
         ->  Sort  (cost=616.56..620.45 rows=1555 width=12) (actual time=45.720..53.265 rows=6407 loops=1)
               Sort Key: latest_download.host_id
               ->  Subquery Scan latest_download  (cost=499.13..534.12 rows=1555 width=12) (actual time=42.867..44.763 rows=472 loops=1)
                     ->  HashAggregate  (cost=499.13..518.57 rows=1555 width=16) (actual time=42.862..43.628 rows=472 loops=1)
                           ->  Hash Join  (cost=5.64..477.57 rows=2875 width=16) (actual time=0.206..41.503 rows=623 loops=1)
                                 Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
                                 ->  Seq Scan on software_download  (cost=0.00..377.78 rows=13080 width=16) (actual time=0.007..23.494 rows=13167 loops=1)
                                       Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
                                 ->  Hash  (cost=5.59..5.59 rows=20 width=4) (actual time=0.155..0.155 rows=22 loops=1)
                                       ->  Seq Scan on software_binary  (cost=0.00..5.59 rows=20 width=4) (actual time=0.011..0.112 rows=22 loops=1)
                                             Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
   ->  Hash  (cost=6418.20..6418.20 rows=1 width=20) (actual time=437.111..437.111 rows=238 loops=1)
         ->  Merge Join  (cost=6149.96..6418.20 rows=1 width=20) (actual time=367.555..436.667 rows=238 loops=1)
               Merge Cond: (("outer".rmsbinaryid = "inner".rmsbinaryid) AND ("outer".msgid = "inner".msgid) AND ("outer".entityid = "inner".entityid))
               ->  Sort  (cost=2119.55..2121.03 rows=593 width=16) (actual time=117.104..117.476 rows=323 loops=1)
                     Sort Key: a1.rmsbinaryid, a1.msgid, a1.entityid
                     ->  Hash Join  (cost=2054.19..2092.23 rows=593 width=16) (actual time=114.671..116.280 rows=323 loops=1)
                           Hash Cond: ("outer".entityid = "inner".myapp_app_id)
                           ->  HashAggregate  (cost=1994.00..2001.41 rows=593 width=12) (actual time=108.909..109.486 rows=323 loops=1)
                                 ->  Seq Scan on msg306u  (cost=0.00..1797.28 rows=26230 width=12) (actual time=0.009..68.861 rows=25542 loops=1)
                                       Filter: (downloadstatus = '1'::text)
                           ->  Hash  (cost=55.95..55.95 rows=1695 width=8) (actual time=5.736..5.736 rows=1695 loops=1)
                                 ->  Seq Scan on myapp_app ia  (cost=0.00..55.95 rows=1695 width=8) (actual time=0.005..2.850 rows=1695 loops=1)
               ->  Sort  (cost=4030.42..4095.99 rows=26230 width=20) (actual time=250.434..286.311 rows=25542 loops=1)
                     Sort Key: public.msg306u.rmsbinaryid, public.msg306u.msgid, public.msg306u.entityid
                     ->  Seq Scan on msg306u  (cost=0.00..1797.28 rows=26230 width=20) (actual time=0.009..80.478 rows=25542 loops=1)
                           Filter: (downloadstatus <> '0'::text)
 Total runtime: 553.409 ms

Ah, a beautiful scheme!  So given I can't run with enable_nestloop off,
anyone have a suggestion on how to get this thing moving in the right
direction? I tried raising statistics estimates on some of the columns
but that didn't help, though maybe I was raising it on the right
columns.. any suggestions there? Or perhaps a better way to write the
query... I'm open to suggestions. TIA,


Robert Treat
-- 
Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL


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Message-ID: <43C66D67.1000502@elios-informatique.fr>
Date: Thu, 12 Jan 2006 15:53:27 +0100
From: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
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	pgsql-performance@postgresql.org
Subject: Re: Please Help: PostgreSQL performance Optimization
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<html>
<head>
  <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
  <title></title>
</head>
<body bgcolor="#ffffff" text="#000000">
Jamal Ghaffour a &eacute;crit&nbsp;:
<blockquote cite="mid43C66742.9060104@elios-informatique.fr" type="cite">
  <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
  <title></title>
  <font><font color="#000000">
  <pre style="margin: 0em;">Hi,
<font face="Arial, Helvetica, sans-serif">
I'm working on a project, whose implementation deals with PostgreSQL. A brief description of our application is given  below.</font>

I'm running version 8.0 on a dedicated  server 1Gb of RAM. 
my database isn't complex, it contains just 2 simple tables.
<tt>
CREATE TABLE cookies (
    domain varchar(50) NOT NULL,
    path varchar(50) NOT NULL,
    name varchar(50) NOT NULL,
    principalid varchar(50) NOT NULL,
    host text NOT NULL,
    value text NOT NULL,
    secure bool NOT NULL,
    timestamp timestamp with time zone NOT NULL DEFAULT 
CURRENT_TIMESTAMP+TIME '04:00:00',
    PRIMARY KEY  (domain,path,name,principalid)
)

CREATE TABLE liberty (
    principalid varchar(50) NOT NULL,
    requestid varchar(50) NOT NULL,
    spassertionurl text NOT NULL,
    libertyversion  varchar(50) NOT NULL,
    relaystate  varchar(50) NOT NULL,
    PRIMARY KEY  (principalid)
)

</tt>I'm developping an application that uses the libpqxx to execute 
psql queries on the database and have to execute 500 requests at the same time.

<tt>
UPDATE cookies SET host='ping.icap-elios.com', value= '54E5B5491F27C0177083795F2E09162D', secure=FALSE, 
timestamp=CURRENT_TIMESTAMP+INTERVAL '14400 SECOND' WHERE 
domain='ping.icap-elios.com' AND path='/tfs' AND principalid='192.168.8.219' AND 
name='jsessionid'</tt>

<tt>SELECT path, upper(name) AS name, value FROM cookies  WHERE timestamp&lt;CURRENT_TIMESTAMP AND principalid='192.168.8.219' AND 
secure=FALSE AND (domain='ping.icap-elios.com' OR domain='.icap-elios.com')</tt>

I have to notify that the performance of is extremely variable and irregular.
I can also see that the server process uses almost 100% of
a CPU.

I'm using the default configuration file, and i m asking if i have to change some paramters to have a good performance.

Any help would be greatly appreciated.

Thanks,</pre>
  </font></font>
</blockquote>
Hi,<br>
<br>
There are some results that can give you <span class="def-example">concrete&nbsp;</span>
idea about my problem: <br>
when i 'm launching my test that executes in loop manner the&nbsp; SELECT
and UPDATE queries described above, i'm obtaining this results:<br>
<br>
UPDATE Time execution :0s: 5225 us<br>
SELECT Time execution&nbsp; :0s: 6908 us<br>
<br>
5 minutes Later: <br>
<br>
UPDATE Time execution :0s: 6125 us<br>
SELECT Time execution&nbsp; :0s: 10928 us<br>
<br>
5 minutes Later: <br>
<br>
UPDATE Time execution :0s: 5825 us<br>
SELECT Time execution&nbsp; :0s: 14978 us<br>
<br>
As you can see , the time execution of the SELECT request is growing
relatively to time and not the UPDATE time execution. <br>
&nbsp;I note that to stop the explosion of the Select time execution, i m
using frequently the vaccum query on the cookies table.<br>
Set&nbsp; the&nbsp; autovacuum parmaeter in the configuation file to on wasn't
able to remplace the use of the vaccum command, and i don't know if
this behaivour is normal?<br>
<br>
Thanks,<br>
Jamal<br>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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=?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com> writes:
> As far as I know SQL Server has some similar feature. It does not join
> if not necessary, more exactly: if the result would be the same if it
> joined the table.

I find it really really hard to believe that such cases arise often
enough to justify having the planner spend cycles checking for them.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Thu Jan 12 12:25:54 2006
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Dear Tom,

Not sure about Otto's exact problem, but he did mention views, and I'd feel 
more comfortable if you told me that view-based queries are re-planned based 
on actual conditions etc. Are they?

Also, if you find it unlikely (or very rare) then it might be a configurable 
parameter. If someone finds it drastically improving (some of) their 
queries, it'd be possible to enable this feature in expense of extra planner 
cycles (on all queries).

What I'd be concerned about, is whether the developers' time spent on this 
feature would worth it. :)

--
G.


On 2006.01.12. 16:53, Tom Lane wrote:
> =?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com> writes:
>> As far as I know SQL Server has some similar feature. It does not join
>> if not necessary, more exactly: if the result would be the same if it
>> joined the table.
> 
> I find it really really hard to believe that such cases arise often
> enough to justify having the planner spend cycles checking for them.
> 
> 			regards, tom lane


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From: =?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com>
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Hi,

I think it would be sufficient only for views. In other cases the
programmer can optimize himself. But a view can be a join of other
tables, and it is not sure that all of them are always needed. It all
depends on what I select from the view.
This information could even be calculted at view creation time. Of
cource this requires that views are handled in a bit more special way,
not just a view definition that is substituted into the original query
(as far as I know the current implementation is similar to this. Sorry
if not).
What do you think about this idea? Of course it is not trivial to
implement, but the result is really great.

Postgres could determine at creation time, if this kind of
optimization is possible at all or not. It can happan though that not
all information is available (I mean unique index or foreign key) at
that time. So this optimiztaion info could be refreshed later by a
command, "ALTER VIEW <viewname> ANALYZE" or "ANALYZE <view name>"
simply.
Postgres could also establish at creation time that for a given column
in the selection list which source table(s) are required. This is
probably not sufficient, but I haven't thought is through thouroughly
yet. And I am not that familiar with the current optimizer internals.
And one should be able to turn off this optimization, so that view
creation takes not longer than now. If the optimizer finds no
optimization info in the catalog, it behaves like now.
I hope you see this worth.
This all is analogue to statistics collection.

Thanks for reading,
Otto


2006/1/12, Tom Lane <tgl@sss.pgh.pa.us>:
> =3D?ISO-8859-1?Q?Ott=3DF3_Havasv=3DF6lgyi?=3D <havasvolgyi.otto@gmail.com=
> writes:
> > As far as I know SQL Server has some similar feature. It does not join
> > if not necessary, more exactly: if the result would be the same if it
> > joined the table.
>
> I find it really really hard to believe that such cases arise often
> enough to justify having the planner spend cycles checking for them.
>
>                        regards, tom lane
>

From pgsql-performance-owner@postgresql.org  Thu Jan 12 13:03:09 2006
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Subject: Re: Throwing unnecessary joins away
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On Thu, 2006-01-12 at 11:00, Ott=C3=B3 Havasv=C3=B6lgyi wrote:
> Hi,
>=20
> I think it would be sufficient only for views. In other cases the
> programmer can optimize himself. But a view can be a join of other
> tables, and it is not sure that all of them are always needed. It all
> depends on what I select from the view.

The idea that you could throw away joins only works for outer joins.=20
I.e. if you did:

select a.x, a.y, a.z from a left join b (on a.id=3Db.aid)=20

then you could throw away the join to b.  But if it was a regular inner
join then you couldn't know whether or not you needed to join to b
without actually joining to b...

From pgsql-performance-owner@postgresql.org  Thu Jan 12 14:34:17 2006
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Date: Thu, 12 Jan 2006 10:42:39 -0800
From: Andrew Lazarus <andrew@pillette.com>
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Organization: Pillette Investment Management
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To: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
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Subject: Re: Please Help: PostgreSQL performance Optimization
References: <43C66742.9060104@elios-informatique.fr>
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Jamal Ghaffour wrote:

>>CREATE TABLE cookies (
>>    domain varchar(50) NOT NULL,
>>    path varchar(50) NOT NULL,
>>    name varchar(50) NOT NULL,
>>    principalid varchar(50) NOT NULL,
>>    host text NOT NULL,
>>    value text NOT NULL,
>>    secure bool NOT NULL,
>>    timestamp timestamp with time zone NOT NULL DEFAULT 
>>CURRENT_TIMESTAMP+TIME '04:00:00',
>>    PRIMARY KEY  (domain,path,name,principalid)
>>)
[snip]
>>SELECT path, upper(name) AS name, value FROM cookies  WHERE timestamp<CURRENT_TIMESTAMP AND principalid='192.168.8.219' AND 
>>secure=FALSE AND (domain='ping.icap-elios.com' OR domain='.icap-elios.com')

I think the problem here is that the column order in the index doesn't 
match the columns used in the WHERE clause criteria. Try adding an index 
on (domain,principalid) or (domain,principalid,timestamp). If these are 
your only queries, you can get the same effect by re-ordering the 
columns in the table so that this is the column order used by the 
primary key and its implicit index.

You should check up on EXPLAIN and EXPLAIN ANALYZE to help you debug 
slow queries.

--------------010002000102050508090103
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begin:vcard
fn:Andrew Lazarus
n:Lazarus;Andrew
org:Pillette Investment Management;Research and Development
adr;dom:;;3028 Fillmore;San Francisco;CA;94123
email;internet:andrew@pillette.com
title:Director
tel;work:800-366-0688
tel;fax:415-440-4093
url:http://www.pillette.com
version:2.1
end:vcard


--------------010002000102050508090103--

From pgsql-performance-owner@postgresql.org  Thu Jan 12 14:51:27 2006
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Hi,

If the join is to a primary key or notnull unique column(s), then
inner join is also ok. But of course left join is the simpler case.
An example:

create table person (id serial primary key, name varchar not null);
create table pet (id serial primary key, name varchar not null,
person_id int not null references person(id));
create view v_pet_person as select pet.id as pet_id, pet.name as
pet_name, person_id as person_id, person.name as person_name from pet
join person (pet.person_id=3Dperson.id);

At this point we know that optimization may be possible because of the
primary key on person. The optimization depends on the primary key
constraint. Kindof internal dependency.
We can find out that which "from-element" is a given field's source as
far they are simple references. This can be stored.
Then query the view:

select pet_name, person_id from v_pet_person where person_id=3D2;

In this case we don't need the join.
These queries are usually dynamically generated, the selection list
and the where condition is the dynamic part.

Best Regards,
Otto


2006/1/12, Scott Marlowe <smarlowe@g2switchworks.com>:
> On Thu, 2006-01-12 at 11:00, Ott=F3 Havasv=F6lgyi wrote:
> > Hi,
> >
> > I think it would be sufficient only for views. In other cases the
> > programmer can optimize himself. But a view can be a join of other
> > tables, and it is not sure that all of them are always needed. It all
> > depends on what I select from the view.
>
> The idea that you could throw away joins only works for outer joins.
> I.e. if you did:
>
> select a.x, a.y, a.z from a left join b (on a.id=3Db.aid)
>
> then you could throw away the join to b.  But if it was a regular inner
> join then you couldn't know whether or not you needed to join to b
> without actually joining to b...
>

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Date: Thu, 12 Jan 2006 13:16:18 -0600
From: Kenneth Marshall <ktm@it.is.rice.edu>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Jean-Philippe C?t? <jean-philippe.cote@crt.umontreal.ca>,
	pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance
Message-ID: <20060112191618.GB81@it.is.rice.edu>
References: <20060111234149.05DEA384099@crt0.crt.umontreal.ca>
	<480.1137036235@sss.pgh.pa.us>
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On Thu, Jan 12, 2006 at 09:48:41AM +0000, Simon Riggs wrote:
> On Wed, 2006-01-11 at 22:23 -0500, Tom Lane wrote:
> > =?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> > > Thanks a lot for this info, I was indeed exceeding the genetic
> > > optimizer's threshold.  Now that it is turned off, I get
> > > a very stable response time of 435ms (more or less 5ms) for
> > > the same query. It is about three times slower than the best
> > > I got with the genetic optimizer on, but the overall average
> > > is much lower.
> > 
> > Hmm.  It would be interesting to use EXPLAIN ANALYZE to confirm that the
> > plan found this way is the same as the best plan found by GEQO, and
> > the extra couple hundred msec is the price you pay for the exhaustive
> > plan search.  If GEQO is managing to find a plan better than the regular
> > planner then we need to look into why ...
> 
> It seems worth noting in the EXPLAIN whether GEQO has been used to find
> the plan, possibly along with other factors influencing the plan such as
> enable_* settings.
> 

Is it the plan that is different in the fastest case with GEQO or is it
the time needed to plan that is causing the GEQO to beat the exhaustive
search?

Ken


From pgsql-performance-owner@postgresql.org  Thu Jan 12 16:16:06 2006
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Date: Thu, 12 Jan 2006 15:16:00 -0500
From: Jaime Casanova <systemguards@gmail.com>
To: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
Subject: Re: Please Help: PostgreSQL performance Optimization
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On 1/12/06, Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr> wrote:
> Jamal Ghaffour a =E9crit :
> Hi,

I'm working on a project, whose implementation deals with PostgreSQL. A
> brief description of our application is given below.

I'm running version
> 8.0 on a dedicated server 1Gb of RAM.
my database isn't complex, it
> contains just 2 simple tables.

CREATE TABLE cookies (
 domain varchar(50)
> NOT NULL,
 path varchar(50) NOT NULL,
 name varchar(50) NOT NULL,
> principalid varchar(50) NOT NULL,
 host text NOT NULL,
 value text NOT
> NULL,
 secure bool NOT NULL,
 timestamp timestamp with time zone NOT NULL
> DEFAULT
CURRENT_TIMESTAMP+TIME '04:00:00',
 PRIMARY KEY
> (domain,path,name,principalid)
)

CREATE TABLE liberty (
 principalid
> varchar(50) NOT NULL,
 requestid varchar(50) NOT NULL,
 spassertionurl text
> NOT NULL,
 libertyversion varchar(50) NOT NULL,
 relaystate varchar(50) NOT
> NULL,
 PRIMARY KEY (principalid)
)

I'm developping an application that uses
> the libpqxx to execute
psql queries on the database and have to execute 500
> requests at the same time.


UPDATE cookies SET host=3D'ping.icap-elios.com',
> value=3D '54E5B5491F27C0177083795F2E09162D', secure=3DFALSE,
>
timestamp=3DCURRENT_TIMESTAMP+INTERVAL '14400 SECOND' WHERE
>
domain=3D'ping.icap-elios.com' AND path=3D'/tfs' AND
> principalid=3D'192.168.8.219' AND
name=3D'jsessionid'

SELECT path, upper(name)
> AS name, value FROM cookies WHERE timestamp<CURRENT_TIMESTAMP AND
> principalid=3D'192.168.8.219' AND
secure=3DFALSE AND
> (domain=3D'ping.icap-elios.com' OR domain=3D'.icap-elios.com')

I have to notify
> that the performance of is extremely variable and irregular.
I can also see
> that the server process uses almost 100% of
a CPU.

I'm using the default
> configuration file, and i m asking if i have to change some paramters to
> have a good performance.

Any help would be greatly appreciated.

Thanks,
> Hi,
>
> There are some results that can give you concrete  idea about my problem:
> when i 'm launching my test that executes in loop manner the  SELECT and
> UPDATE queries described above, i'm obtaining this results:
>
> UPDATE Time execution :0s: 5225 us
> SELECT Time execution  :0s: 6908 us
>
> 5 minutes Later:
>
> UPDATE Time execution :0s: 6125 us
> SELECT Time execution  :0s: 10928 us
>
> 5 minutes Later:
>
> UPDATE Time execution :0s: 5825 us
> SELECT Time execution  :0s: 14978 us
>
> As you can see , the time execution of the SELECT request is growing
> relatively to time and not the UPDATE time execution.
>  I note that to stop the explosion of the Select time execution, i m usin=
g
> frequently the vaccum query on the cookies table.
> Set  the  autovacuum parmaeter in the configuation file to on wasn't able=
 to
> remplace the use of the vaccum command, and i don't know if this behaivou=
r
> is normal?
>
> Thanks,
> Jamal
>
>

please execute

EXPLAIN ANALYZE <your query>
and show the results, is the only way to know what's happening

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)

From pgsql-performance-owner@postgresql.org  Thu Jan 12 16:14:00 2006
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To: "'Kenneth Marshall'" <ktm@it.is.rice.edu>,
	"'Simon Riggs'" <simon@2ndquadrant.com>
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Subject: Re: Extremely irregular query performance
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Can I actully know whether a given plan is excuted with GEQO on ?
In other words, if I launch 'explain <query>', I'll get a given plan, but if I re-launch
the <query> (withtout the 'explain' keyword), could I get a different
plan given that GEQO induces some randomness ?

>Is it the plan that is different in the fastest case with GEQO or is it
>the time needed to plan that is causing the GEQO to beat the exhaustive
>search?



From pgsql-performance-owner@postgresql.org  Sat Jan 14 01:50:35 2006
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From: Kenneth Marshall <ktm@it.is.rice.edu>
To: Jean-Philippe Cote <jean-philippe.cote@crt.umontreal.ca>
Cc: 'Simon Riggs' <simon@2ndquadrant.com>, pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance
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On Thu, Jan 12, 2006 at 03:23:14PM -0500, Jean-Philippe Cote wrote:
> 
> 
> Can I actully know whether a given plan is excuted with GEQO on ?
> In other words, if I launch 'explain <query>', I'll get a given plan, but if I re-launch
> the <query> (withtout the 'explain' keyword), could I get a different
> plan given that GEQO induces some randomness ?
> 
> >Is it the plan that is different in the fastest case with GEQO or is it
> >the time needed to plan that is causing the GEQO to beat the exhaustive
> >search?
> 
GEQO will be used if the number of joins is over the GEQO limit in
the configuration file. The GEQO process is an iterative random
process to find an query plan. The EXPLAIN results are the plan for that
query, but not neccessarily for subsequent runs. GEQO's advantage is a
much faster plan time than the exhaustive search method normally used.
If the resulting plan time is less than the exhaustive search plan time,
for short queries you can have the GECO run more quickly than the
exhaustive search result. Of course, if you PREPARE the query the plan
time drops out.

Ken

From pgsql-performance-owner@postgresql.org  Fri Jan 13 05:10:53 2006
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Date: Fri, 13 Jan 2006 10:13:37 +0100
From: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
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Andrew Lazarus a �crit :

> Jamal Ghaffour wrote:
>
>>> CREATE TABLE cookies (
>>>    domain varchar(50) NOT NULL,
>>>    path varchar(50) NOT NULL,
>>>    name varchar(50) NOT NULL,
>>>    principalid varchar(50) NOT NULL,
>>>    host text NOT NULL,
>>>    value text NOT NULL,
>>>    secure bool NOT NULL,
>>>    timestamp timestamp with time zone NOT NULL DEFAULT 
>>> CURRENT_TIMESTAMP+TIME '04:00:00',
>>>    PRIMARY KEY  (domain,path,name,principalid)
>>> )
>>
> [snip]
>
>>> SELECT path, upper(name) AS name, value FROM cookies  WHERE 
>>> timestamp<CURRENT_TIMESTAMP AND principalid='192.168.8.219' AND 
>>> secure=FALSE AND (domain='ping.icap-elios.com' OR 
>>> domain='.icap-elios.com')
>>
>
> I think the problem here is that the column order in the index doesn't 
> match the columns used in the WHERE clause criteria. Try adding an 
> index on (domain,principalid) or (domain,principalid,timestamp). If 
> these are your only queries, you can get the same effect by 
> re-ordering the columns in the table so that this is the column order 
> used by the primary key and its implicit index.
>
> You should check up on EXPLAIN and EXPLAIN ANALYZE to help you debug 
> slow queries.

Hi,
I created an index into the cookies table
CREATE INDEX index_cookies_select ON cookies (domain, principalid, 
timestamp);
and execute my UPDATE and select queries:

1 - The first select quey give the following results:

icap=# EXPLAIN ANALYZE SELECT path, upper(name) AS name, value FROM 
cookies WHERE timestamp>CURRENT_TIMESTAMP AND 
principalid='192.168.8.219' AND secure=FALSE AND 
(domain='ping.icap-elios.com' OR domain='.icap-elios.com');
                                                                                                                                    
QUERY 
PLAN                                                                                                                              

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on cookies  (cost=4.02..8.04 rows=1 width=268) (actual 
time=0.107..0.108 rows=1 loops=1)
   Recheck Cond: (((("domain")::text = 'ping.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())) 
OR ((("domain")::text = '.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())))
   Filter: (("timestamp" > now()) AND (NOT secure))
   ->  BitmapOr  (cost=4.02..4.02 rows=1 width=0) (actual 
time=0.091..0.091 rows=0 loops=1)
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=0.077..0.077 rows=1 loops=1)
               Index Cond: ((("domain")::text = 
'ping.icap-elios.com'::text) AND ((principalid)::text = 
'192.168.8.219'::text) AND ("timestamp" > now()))
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=0.012..0.012 rows=0 loops=1)
               Index Cond: ((("domain")::text = '.icap-elios.com'::text) 
AND ((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now()))
 Total runtime: 0.155 ms
(9 rows)
 
2- After that, i launch my test code  that execute continuely the UPDATE 
and select queries (in loop manner), after 1 minute of continuous 
execution, i obtain the following result:
icap=# EXPLAIN ANALYZE SELECT path, upper(name) AS name, value FROM 
cookies WHERE timestamp>CURRENT_TIMESTAMP AND 
principalid='192.168.8.219' AND secure=FALSE AND 
(domain='ping.icap-elios.com' OR domain='.icap-elios.com');
                                                                                                                                    
QUERY 
PLAN                                                                                                                              

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on cookies  (cost=4.02..8.04 rows=1 width=268) (actual 
time=39.545..39.549 rows=1 loops=1)
   Recheck Cond: (((("domain")::text = 'ping.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())) 
OR ((("domain")::text = '.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())))
   Filter: (("timestamp" > now()) AND (NOT secure))
   ->  BitmapOr  (cost=4.02..4.02 rows=1 width=0) (actual 
time=39.512..39.512 rows=0 loops=1)
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=39.471..39.471 rows=2 loops=1)
               Index Cond: ((("domain")::text = 
'ping.icap-elios.com'::text) AND ((principalid)::text = 
'192.168.8.219'::text) AND ("timestamp" > now()))
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=0.036..0.036 rows=0 loops=1)
               Index Cond: ((("domain")::text = '.icap-elios.com'::text) 
AND ((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now()))
 Total runtime: 39.616 ms
(9 rows)

I notice that the time execution increases significantly.  and i need 
the vacuum query to obtain normal time execution:


3- After vacuum execution:
icap=# vacuum cookies;
VACUUM
icap=# EXPLAIN ANALYZE SELECT path, upper(name) AS name, value FROM 
cookies WHERE timestamp>CURRENT_TIMESTAMP AND 
principalid='192.168.8.219' AND secure=FALSE AND 
(domain='ping.icap-elios.com' OR domain='.icap-elios.com');
                                                                                                                                    
QUERY 
PLAN                                                                                                                              

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on cookies  (cost=4.02..8.04 rows=1 width=268) (actual 
time=0.111..0.112 rows=1 loops=1)
   Recheck Cond: (((("domain")::text = 'ping.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())) 
OR ((("domain")::text = '.icap-elios.com'::text) AND 
((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now())))
   Filter: (("timestamp" > now()) AND (NOT secure))
   ->  BitmapOr  (cost=4.02..4.02 rows=1 width=0) (actual 
time=0.095..0.095 rows=0 loops=1)
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=0.081..0.081 rows=1 loops=1)
               Index Cond: ((("domain")::text = 
'ping.icap-elios.com'::text) AND ((principalid)::text = 
'192.168.8.219'::text) AND ("timestamp" > now()))
         ->  Bitmap Index Scan on index_cookies_select  (cost=0.00..2.01 
rows=1 width=0) (actual time=0.012..0.012 rows=0 loops=1)
               Index Cond: ((("domain")::text = '.icap-elios.com'::text) 
AND ((principalid)::text = '192.168.8.219'::text) AND ("timestamp" > now()))
 Total runtime: 0.159 ms
(9 rows)



Thanks,
Jamal


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email;internet:Jamal.Ghaffour@elios-informatique.fr
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From pgsql-performance-owner@postgresql.org  Fri Jan 13 13:41:06 2006
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Date: Fri, 13 Jan 2006 11:41:26 -0600
From: Frank Wiles <frank@wiles.org>
To: Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr>
Cc: pgsql-performance@postgresql.org
Subject: Re: Please Help: PostgreSQL performance Optimization
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On Thu, 12 Jan 2006 01:32:10 +0100
Jamal Ghaffour <Jamal.Ghaffour@elios-informatique.fr> wrote:

> I'm using the default configuration file, and i m asking if i have to
> change some paramters to have a good performance.

  In general the answer is yes.  The default is a pretty good best guess
  at what sorts of values work for your "typical system", but if you run
  into performance problems the config file is where you should look
  first, provided you've done the simple things like adding good
  indexes, vacumm analyze, etc. 

  You'll want to consult the following various documentation out there
  to help your properly tune your configuration: 

  http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html
  http://www.powerpostgresql.com/Docs
  http://www.powerpostgresql.com/PerfList
  http://www.revsys.com/writings/postgresql-performance.html

  Hopefully these will help you understand how to set your configuration
  values. 

 ---------------------------------
   Frank Wiles <frank@wiles.org>
   http://www.wiles.org
 ---------------------------------


From pgsql-performance-owner@postgresql.org  Fri Jan 13 16:10:38 2006
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From: Michael Stone <mstone+postgres@mathom.us>
Subject: insert without oids
To: pgsql-performance@postgresql.org
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OIDs seem to be on their way out, and most of the time you can get a
more helpful result by using a serial primary key anyway, but I wonder
if there's any extension to INSERT to help identify what unique id a
newly-inserted key will get? Using OIDs the insert would return the OID
of the inserted row, which could be useful if you then want to refer to
that row in a subsequent operation. You could get the same result by
manually retrieving the next number in the sequence and using that value
in the insert, but at the cost of additional DB operations. Are there
plans on updating the insert API for the post-OID world?

Mike Stone

From pgsql-performance-owner@postgresql.org  Fri Jan 13 16:20:13 2006
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From: Michael Fuhr <mike@fuhr.org>
To: pgsql-performance@postgresql.org
Subject: Re: insert without oids
Message-ID: <20060113201958.GA99082@winnie.fuhr.org>
References: <20060113201011.GI1408@mathom.us>
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On Fri, Jan 13, 2006 at 03:10:11PM -0500, Michael Stone wrote:
> Are there plans on updating the insert API for the post-OID world?

Are you looking for this TODO item?

* Allow INSERT/UPDATE ... RETURNING new.col or old.col

  This is useful for returning the auto-generated key for an INSERT.
  One complication is how to handle rules that run as part of the
  insert.

http://www.postgresql.org/docs/faqs.TODO.html

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Fri Jan 13 17:28:35 2006
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Subject: Re: insert without oids
From: Neil Conway <neilc@samurai.com>
To: Michael Stone <mstone+postgres@mathom.us>
Cc: pgsql-performance@postgresql.org
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On Fri, 2006-01-13 at 15:10 -0500, Michael Stone wrote:
> OIDs seem to be on their way out, and most of the time you can get a
> more helpful result by using a serial primary key anyway, but I wonder
> if there's any extension to INSERT to help identify what unique id a
> newly-inserted key will get? Using OIDs the insert would return the OID
> of the inserted row, which could be useful if you then want to refer to
> that row in a subsequent operation. You could get the same result by
> manually retrieving the next number in the sequence and using that value
> in the insert, but at the cost of additional DB operations.

There's really no additional operations required:

INSERT INTO t1 VALUES (...);
INSERT INTO t2 VALUES (currval('t1_id_seq'), ...);

You need a separate SELECT if you want to use the generated sequence
value outside the database, although the INSERT ... RETURNING extension
will avoid that (there's a patch implementing this, although it is not
yet in CVS).

-Neil



From pgsql-performance-owner@postgresql.org  Fri Jan 13 18:48:11 2006
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Subject: Re: insert without oids
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On Fri, Jan 13, 2006 at 04:29:15PM -0500, Neil Conway wrote:
>There's really no additional operations required:
>INSERT INTO t2 VALUES (currval('t1_id_seq'), ...);
>You need a separate SELECT if you want to use the generated sequence
>value outside the database, 

That would, of course, be the goal. IOW, if you have a table which has
data which is unique only for the serial column, the old syntax provided
a way to refer to the newly inserted row uniquely without any additional
operations. 

>although the INSERT ... RETURNING extension will avoid that 

That sounds promising. I'll have to put the TODO list on my todo list.
:)

Mike Stone

From pgsql-performance-owner@postgresql.org  Fri Jan 13 19:34:57 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Bendik Rognlien Johansen <bendik.johansen@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Slow query with joins
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On Wed, Jan 11, 2006 at 10:30:58PM +0100, Bendik Rognlien Johansen wrote:
> The sort is definitively the culprit. When I removed it the query was  
> instant. I tried setting work_mem = 131072 but it did not seem to  
> help. I really don't understand this :-( Any other ideas?

What's explain analyze show with the sort in?
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 13 20:06:57 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Mark Liberman <mliberman@mixedsignals.com>,
	pgsql-performance@postgresql.org
Subject: Re: Stable function being evaluated more than once in a single query
Message-ID: <20060114000640.GN9017@pervasive.com>
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	<935.1137040403@sss.pgh.pa.us>
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On Wed, Jan 11, 2006 at 11:33:23PM -0500, Tom Lane wrote:
> Mark Liberman <mliberman@mixedsignals.com> writes:
> > I've got a set-returning function,  defined as STABLE, that I reference twice
> > within a single query, yet appears to be evaluated via two seperate function 
> > scans.
> 
> There is no guarantee, express or implied, that this won't be the case.
> 
> (Seems like we just discussed this a couple days ago...)

Well, from 32.6:

"This category allows the optimizer to optimize away multiple calls of
the function within a single query."

That could certainly be read as indicating that if the function is used
twice in one query it could be optimized to one call.

Is the issue that the optimizer won't combine two function calls (ie:
SELECT foo(..) ... WHERE foo(..)), or is it that sometimes it won't make
the optimization (maybe depending on the query plan, for example)?
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 13 20:18:01 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Alessandro Baretta <a.baretta@barettadeit.com>
Cc: Ott? Havasv?lgyi <havasvolgyi.otto@gmail.com>,
	pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
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On Thu, Jan 12, 2006 at 01:35:07PM +0100, Alessandro Baretta wrote:
> Ott? Havasv?lgyi wrote:
> >Hi all,
> > 
> >Is PostgreSQL able to throw unnecessary joins?
> >For example I have two tables, and I join then with their primary keys, 
> >say type of bigint . In this case if I don't reference to one of the 
> >tables anywhere except the join condition, then the join can be eliminated.
> >Or if I do a "table1 left join table2 (table1.referer=table2.id)"  (N : 
> >1 relationship), and I don't reference table2 anywhere else, then it is 
> >unnecessary.
> 
> It cannot possibly remove "unnecessary joins", simply because the join 
> influences whether a tuple in the referenced table gets selected and how 
> many times.

It can remove them if it's an appropriate outer join, or if there is
appropriate RI that proves that the join won't change what data is
selected.

A really common example of this is creating views that pull in tables
that have text names to go with id's, ie:

CREATE TABLE bug_status(
    bug_status_id       serial  PRIMARY KEY
    , bug_status_name   text    NOT NULL UNIQUE
);

CREATE TABLE bug(
    ...
    , bug_status_id     int     REFERENCES bug_status(bug_status_id)
);

CREATE VIEW bug_v AS
    SELECT b.*, bs.bug_status_name FROM bug b JOIN bug_status NATURAL
;

If you have a bunch of cases like that and start building views on views
it's very easy to end up in situations where you don't have any need of
bug_status_name at all. And because of the RI, you know that removing
the join can't possibly change the bug.* portion of that view.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 13 20:22:09 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Ott? Havasv?lgyi <havasvolgyi.otto@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
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On Thu, Jan 12, 2006 at 07:51:22PM +0100, Ott? Havasv?lgyi wrote:
> Hi,
> 
> If the join is to a primary key or notnull unique column(s), then
> inner join is also ok. But of course left join is the simpler case.
> An example:

Actually, you need both the unique/pk constraint, and RI (a fact I
missed in the email I just sent). Nullability is another consideration
as well. But there certainly are some pretty common cases that can be
optimized for.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 13 20:27:32 2006
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To: "Jim C. Nasby" <jnasby@pervasive.com>
cc: Mark Liberman <mliberman@mixedsignals.com>,
	pgsql-performance@postgresql.org
Subject: Re: Stable function being evaluated more than once in a single query 
In-reply-to: <20060114000640.GN9017@pervasive.com> 
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	<935.1137040403@sss.pgh.pa.us>
	<20060114000640.GN9017@pervasive.com>
Comments: In-reply-to "Jim C. Nasby" <jnasby@pervasive.com>
	message dated "Fri, 13 Jan 2006 18:06:40 -0600"
Date: Fri, 13 Jan 2006 19:27:28 -0500
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"Jim C. Nasby" <jnasby@pervasive.com> writes:
> Is the issue that the optimizer won't combine two function calls (ie:
> SELECT foo(..) ... WHERE foo(..)), or is it that sometimes it won't make
> the optimization (maybe depending on the query plan, for example)?

What the STABLE category actually does is give the planner permission to
use the function within an indexscan qualification, eg,
	WHERE indexed_column = f(42)
Since an indexscan involves evaluating the comparison expression just
once and using its value to search the index, this would be incorrect
if the expression's value might change from row to row.  (For VOLATILE
functions, we assume that the correct behavior is the naive SQL
semantics of actually computing the WHERE clause at each candidate row.)

There is no function cache and no checking for duplicate expressions.
I think we do check for duplicate aggregate expressions, but not
anything else.

			regards, tom lane

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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Mark Liberman <mliberman@mixedsignals.com>,
	pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Stable function being evaluated more than once in a
	single query
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Adding -docs...

On Fri, Jan 13, 2006 at 07:27:28PM -0500, Tom Lane wrote:
> "Jim C. Nasby" <jnasby@pervasive.com> writes:
> > Is the issue that the optimizer won't combine two function calls (ie:
> > SELECT foo(..) ... WHERE foo(..)), or is it that sometimes it won't make
> > the optimization (maybe depending on the query plan, for example)?
> 
> What the STABLE category actually does is give the planner permission to
> use the function within an indexscan qualification, eg,
> 	WHERE indexed_column = f(42)
> Since an indexscan involves evaluating the comparison expression just
> once and using its value to search the index, this would be incorrect
> if the expression's value might change from row to row.  (For VOLATILE
> functions, we assume that the correct behavior is the naive SQL
> semantics of actually computing the WHERE clause at each candidate row.)
> 
> There is no function cache and no checking for duplicate expressions.
> I think we do check for duplicate aggregate expressions, but not
> anything else.
 
In that case I'd say that the sSTABLE section of 32.6 should be changed
to read:

A STABLE function cannot modify the database and is guaranteed to
return the same results given the same arguments for all calls within a
single surrounding query. This category gives the planner permission to
use the function within an indexscan qualification. (Since an indexscan
involves evaluating the comparison expression just once and using its
value to search the index, this would be incorrect if the expression's
value might change from row to row.) There is no function cache and no
checking for duplicate expressions.

I can provide a patch to that effect if it's easier...

On a related note, would it be difficult to recognize multiple calls of
the same function in one query? ISTM that would be a win for all but the
most trivial of functions...
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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From pgsql-performance-owner@postgresql.org  Sat Jan 14 00:23:49 2006
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200601140423.k0E4NX019385@candle.pha.pa.us>
Subject: Re: Extremely irregular query performance
In-Reply-To: <20060112201353.5C39138409A@crt0.crt.umontreal.ca>
To: Jean-Philippe Cote <jean-philippe.cote@crt.umontreal.ca>
Date: Fri, 13 Jan 2006 23:23:33 -0500 (EST)
CC: "'Kenneth Marshall'" <ktm@is.rice.edu>,
	"'Simon Riggs'" <simon@2ndquadrant.com>, pgsql-performance@postgresql.org
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Jean-Philippe Cote wrote:
> 
> 
> Can I actully know whether a given plan is excuted with GEQO on ?
> In other words, if I launch 'explain <query>', I'll get a given plan, but if I re-launch
> the <query> (withtout the 'explain' keyword), could I get a different
> plan given that GEQO induces some randomness ?
> 
> >Is it the plan that is different in the fastest case with GEQO or is it
> >the time needed to plan that is causing the GEQO to beat the exhaustive
> >search?

Yes, is it likely that when using GEQO you would get a different plan
each time, so running it with and without EXPLAIN would produce
different plans.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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Date: Sat, 14 Jan 2006 13:13:02 +0100 (CET)
From: Tomka Gergely <tomka@zeus.gau.hu>
To: psql performance list <pgsql-performance@postgresql.org>
Subject: big databases & hospitals
Message-ID: <Pine.LNX.4.58.0601141307480.26994@zeus.gau.hu>
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Hi!

I need to write a few pages about Postgresql, to convince some suits. They
have a few millions of records, on a few site, but they want to know the
practical limits of Postgresql. So i need some information about the
biggest (in storage space, in record number, in field number, and maybe
table number) postgresql databases.

Additionally, because this company develops hospital information systems,
if someone knows about a medical institute, which uses Postgresql, and
happy, please send me infomation. I only now subscribed to the advocacy
list, and only started to browse the archives.

Thanks.

-- 
Tomka Gergely
Tudom, anyu. Sapka, s�l, doksi.

From pgsql-performance-owner@postgresql.org  Sat Jan 14 10:54:43 2006
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From: "Javier Carlos" <nediam@nediam.com.mx>
To: Tomka Gergely <tomka@zeus.gau.hu>,
	psql performance list <pgsql-performance@postgresql.org>
Subject: Re: big databases & hospitals
Date: Sat, 14 Jan 2006 08:51:46 -0600
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   This is the homepage of a Hospital/Healthservice Information System, I'm
not so sure but I think it can use various DBMS, including PostgreSQL:

http://www.care2x.org/

  Regards,

  Javier



On Sat, 14 Jan 2006 13:13:02 +0100 (CET), Tomka Gergely wrote
> Hi!
> 
> I need to write a few pages about Postgresql, to convince some 
> suits. They have a few millions of records, on a few site, but they 
> want to know the practical limits of Postgresql. So i need some 
> information about the biggest (in storage space, in record number, 
> in field number, and maybe table number) postgresql databases.
> 
> Additionally, because this company develops hospital information 
> systems, if someone knows about a medical institute, which uses 
> Postgresql, and happy, please send me infomation. I only now 
> subscribed to the advocacy list, and only started to browse the archives.
> 
> Thanks.
> 
> -- 
> Tomka Gergely
> Tudom, anyu. Sapka, s�l, doksi.
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match


--
nediam.com.mx


From pgsql-performance-owner@postgresql.org  Sat Jan 14 14:38:12 2006
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	Sat, 14 Jan 2006 19:36:26 +0100
Subject: Re: big databases & hospitals
From: Chris Mair <list@1006.org>
To: Tomka Gergely <tomka@zeus.gau.hu>
Cc: psql performance list <pgsql-performance@postgresql.org>
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> Additionally, because this company develops hospital information systems,
> if someone knows about a medical institute, which uses Postgresql, and
> happy, please send me infomation. I only now subscribed to the advocacy
> list, and only started to browse the archives.

Hi,

have you seen this case study:
http://www.postgresql.org/about/casestudies/shannonmedical

Bye, Chris.



From pgsql-performance-owner@postgresql.org  Sat Jan 14 13:55:55 2006
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From: Tomka Gergely <tomka@zeus.gau.hu>
To: Chris Mair <list@1006.org>
Cc: psql performance list <pgsql-performance@postgresql.org>
Subject: Re: big databases & hospitals
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2006-01-14 ragyog� napj�n Chris Mair ezt �zente:

>
> > Additionally, because this company develops hospital information systems,
> > if someone knows about a medical institute, which uses Postgresql, and
> > happy, please send me infomation. I only now subscribed to the advocacy
> > list, and only started to browse the archives.
>
> Hi,
>
> have you seen this case study:
> http://www.postgresql.org/about/casestudies/shannonmedical

Yes, and i found this page:

http://advocacy.daemonnews.org/viewtopic.php?t=82

which is better than this small something on the postgres page. Quotes
like this:

"The FreeBSD/PostgreSQL combination is extremely flexible and
robust."

the sweetest music for us. But two example better than one, and i can't
find technical details, the size of the data, by example. I can only guess
the architecture (single node, single cpu, no HA or expensive RAID,
because AFAIK FreeBSD in 2000 was not to good in this areas).

Thanks, of course!

-- 
Tomka Gergely
Tudom, anyu. Sapka, s�l, doksi.

From pgsql-performance-owner@postgresql.org  Sat Jan 14 14:05:40 2006
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	Sat, 14 Jan 2006 13:05:35 -0500 (EST)
To: vimal.gupta@gmail.com
cc: pgsql-performance@postgresql.org
Subject: Re: Hanging Query 
In-reply-to: <1136741670.479720.284080@f14g2000cwb.googlegroups.com> 
References: <1136741670.479720.284080@f14g2000cwb.googlegroups.com>
Comments: In-reply-to vimal.gupta@gmail.com
	message dated "08 Jan 2006 09:34:30 -0800"
Date: Sat, 14 Jan 2006 13:05:35 -0500
Message-ID: <20665.1137261935@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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vimal.gupta@gmail.com writes:
> We have to inserts a records(15000- 20000) into a table which also
> contains (15000-20000) records, then after insertion, we have to delete
> the records according to a business rule.
> Above process is taking place in a transaction and we are using batches
> of 128 to insert records.
> Everything works fine on QA environment but somehow after inserts,
> delete query hangs in production environment. Delete query has some
> joins with other table and a self join. There is no exception as we
> have done enough exception handling. It simply hangs with no trace in
> application logs.

> When I do "ps aux" , I see
> postgres  5294 41.3  2.4 270120 38092 pts/4  R    10:41  52:56
> postgres: nuuser nm 127.0.0.1 DELETE

That doesn't look to me like it's "hanging"; it's trying to process
some unreasonably long-running query.  If I were you I'd be taking
a closer look at that DELETE command.  It may contain an unconstrained
join (cross-product) or some such.  Try EXPLAINing the command and
look for unexpected table scans.

> Postgres 7.3.4 on Linux..

That's mighty ancient and has many known bugs.  Do yourself a favor
and update to some newer version --- at the very least, use the latest
7.3 branch release (we're up to 7.3.13 now).

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 14 14:10:32 2006
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To: "Bernard Dhooghe" <dhoogheb@yahoo.com>
cc: pgsql-performance@postgresql.org
Subject: Re: >= forces row compare and not index elements compare when
	possible
In-reply-to: <1136826602.613297.42010@f14g2000cwb.googlegroups.com> 
References: <1136826602.613297.42010@f14g2000cwb.googlegroups.com>
Comments: In-reply-to "Bernard Dhooghe" <dhoogheb@yahoo.com>
	message dated "09 Jan 2006 09:10:02 -0800"
Date: Sat, 14 Jan 2006 13:10:28 -0500
Message-ID: <20702.1137262228@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Bernard Dhooghe" <dhoogheb@yahoo.com> writes:
> So >= (or <=) is not optimized against an index where it could be.

Work in progress...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 14 14:13:42 2006
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From: "Benjamin Arai" <barai@cs.ucr.edu>
To: <pgsql-performance@postgresql.org>
Subject: Ensuring data integrity with fsync=off
Date: Sat, 14 Jan 2006 10:13:27 -0800
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I have been working on optimizing a PostgreSQL server for weekly updates
where data is only updated once a week then for the remaining portion of the
week the data is static.  So far I have set fsync to off and increased the
segment size among other things.  I need to ensure that at the end of the
update each week the data is in state where a crash will not kill the
database.  
 
Right now I run "sync" afte the updates have finished to ensure that the
data is synced to disk but I am concerned about the segment data and
anything else I am missing that PostgreSQL explicitly handles.  Is there
something I can do in addition to sync to tell PostgreSQL exlplicitly that
it is time to ensure everything is stored in its final destionation and etc?
 
Benjamin

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<DIV><SPAN class=3D361280818-14012006><FONT face=3DArial size=3D2>I have =
been working=20
on optimizing a PostgreSQL server for weekly updates where data is only =
updated=20
once a week then for the remaining portion of the week the data is =
static.&nbsp;=20
So far I have set fsync to off and increased the segment size among =
other=20
things.&nbsp; I need to ensure that at the end of the update each =
week&nbsp;the=20
data&nbsp;is in&nbsp;state where a crash will not kill the =
database.&nbsp;=20
</FONT></SPAN></DIV>
<DIV><SPAN class=3D361280818-14012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D361280818-14012006><FONT face=3DArial size=3D2>Right =
now I run=20
"sync" afte the updates have&nbsp;finished to ensure that the data is =
synced to=20
disk but I am concerned about the segment data and anything else I am =
missing=20
that PostgreSQL explicitly handles.&nbsp; Is there something I can do in =

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<DIV><SPAN class=3D361280818-14012006><FONT face=3DArial=20
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From pgsql-performance-owner@postgresql.org  Sat Jan 14 14:41:47 2006
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	message dated "Sat, 14 Jan 2006 10:13:27 -0800"
Date: Sat, 14 Jan 2006 13:41:43 -0500
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"Benjamin Arai" <barai@cs.ucr.edu> writes:
> Right now I run "sync" afte the updates have finished to ensure that the
> data is synced to disk but I am concerned about the segment data and
> anything else I am missing that PostgreSQL explicitly handles.  Is there
> something I can do in addition to sync to tell PostgreSQL exlplicitly that
> it is time to ensure everything is stored in its final destionation and etc?

You need to give PG a CHECKPOINT command to flush stuff out of its
internal buffers.  After that finishes, a manual "sync" commnd will
push everything down to disk.

You realize, of course, that a system failure while the updates are
running might leave your database corrupt?  As long as you are prepared
to restore from scratch, this might be a good tradeoff ... but don't
let yourself get caught without an up-to-date backup ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 14 16:31:45 2006
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Date: Sat, 14 Jan 2006 15:31:43 -0500
From: Jaime Casanova <systemguards@gmail.com>
To: Tomka Gergely <tomka@zeus.gau.hu>
Subject: Re: big databases & hospitals
Cc: psql performance list <pgsql-performance@postgresql.org>
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On 1/14/06, Tomka Gergely <tomka@zeus.gau.hu> wrote:
> Hi!
>
> I need to write a few pages about Postgresql, to convince some suits. The=
y
> have a few millions of records, on a few site, but they want to know the
> practical limits of Postgresql. So i need some information about the
> biggest (in storage space, in record number, in field number, and maybe
> table number) postgresql databases.
>

here you can see some limits of postgresql:
http://www.postgresql.org/about/


--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)

From pgsql-performance-owner@postgresql.org  Sat Jan 14 22:37:02 2006
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From: Charles Sprickman <spork@bway.net>
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Subject: Re: SAN/NAS options
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Following up to myself again...

On Wed, 14 Dec 2005, Charles Sprickman wrote:

> Hello all,
>
> Supermicro 1U w/SCA backplane and 4 bays
> 2x2.8 GHz Xeons
> Adaptec 2015S "zero channel" RAID card

I don't want to throw away the four machines like that that we have.  I do 
want to throw away the ZCR cards... :)  If I ditch those I still have a 1U 
box with a U320 scsi plug on the back.

I'm vaguely considering pairing these two devices:

http://www.areca.us/products/html/products.htm

That's an Areca 16 channel SATA II (I haven't even read up on what's new 
in SATA II) RAID controller with an optional U320 SCSI daughter card to 
connect to the host(s).

http://www.chenbro.com.tw/Chenbro_Special/RM321.php

How can I turn that box down?  Those people in the picture look very 
excited about it?  Seriously though, it looks like an interesting and 
economical pairing that gives me most of what I'm looking for:

-a modern RAID engine
-small form factor
-remote management of the array
-ability to reuse my current db hosts that are disk-bound

Disadvantages:

-only 1 or 2 hosts per box
-more difficult to move storage from host to host (compared to a SAN or 
NAS system)
-no fancy NetApp features like snapshots
-I have no experience with Areca SATA->SCSI RAID controllers

Any thoughts on this?  The controller looks to be about $1500, the 
enclosure about $400, and the drives are no great mystery, cost would 
depend on what total capacity I'm looking for.

Our initial plan is to set one up for storage for a mail archive project, 
and to also have a host use this storage to host replicated copies of all 
Postgres databases.  If things look good, we'd start moving our main PG 
hosts to use a similar RAID box.

Thanks,

Charles


From pgsql-performance-owner@postgresql.org  Sat Jan 14 23:34:36 2006
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Date: Sat, 14 Jan 2006 19:02:07 -0800
Subject: Re: SAN/NAS options
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Charles Sprickman" <spork@bway.net>,
	pgsql-performance@postgresql.org
Message-ID: <BFEEFB2F.1A779%llonergan@greenplum.com>
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Charles,

On 1/14/06 6:37 PM, "Charles Sprickman" <spork@bway.net> wrote:

> I'm vaguely considering pairing these two devices:
> 
> http://www.areca.us/products/html/products.htm
> 
> That's an Areca 16 channel SATA II (I haven't even read up on what's new
> in SATA II) RAID controller with an optional U320 SCSI daughter card to
> connect to the host(s).

I'm confused - SATA with a SCSI daughter card? Where does the SCSI go?

The Areca has a number (8,12,16) of single drive attach SATA ports coming
out of it, each of which will go to a disk drive connection on the
backplane.
 
> http://www.chenbro.com.tw/Chenbro_Special/RM321.php
> 
> How can I turn that box down?  Those people in the picture look very
> excited about it?  Seriously though, it looks like an interesting and
> economical pairing that gives me most of what I'm looking for:

What a picture!  I'm totally enthusiastic all of a sudden!  I'm putting !!!
at the end of every sentence!

We just bought 4 very similar systems that use the chassis from California
Design - our latest favorite source:
  http://www.asacomputers.com/

They did an excellent job of setting the systems up, with proper labeling
and Quality Control.  They also installed Fedora Core 4 and set up the
filesystems, the only mistake they made was that they didn't enable 2TB
clipping so that we had to rebuild the RAIDs (and install CentOS with the
xfs filesystem).

We paid $10.4K each for 16x 400GB WD RE2 SATA II drives, 16GB RAM and two
Opteron 250s.  We also put a single 200GB SATA system drive into each.  RAID
card is the 3Ware 9550SX.
 
Performance has been stunning - we're getting 800MB/s sustained I/O
throughput using the two 9550SX controllers in parallel.

> Any thoughts on this?  The controller looks to be about $1500, the
> enclosure about $400, and the drives are no great mystery, cost would
> depend on what total capacity I'm looking for.

I'd get ASA to build it for you - use the Tyan 2882 series motherboard for
greatest stablity.  They may try to sell you hard on the SuperMicro boards,
we've had less luck with them.
 
> Our initial plan is to set one up for storage for a mail archive project,
> and to also have a host use this storage to host replicated copies of all
> Postgres databases.  If things look good, we'd start moving our main PG
> hosts to use a similar RAID box.

Good approach.

I'm personally spending as much time using these machines as I can - they
are the fastest I've been on in a *long* time.
 
- Luke



From pgsql-performance-owner@postgresql.org  Sat Jan 14 23:23:05 2006
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On Sat, 14 Jan 2006, Luke Lonergan wrote:

> Charles,
>
> On 1/14/06 6:37 PM, "Charles Sprickman" <spork@bway.net> wrote:
>
>> I'm vaguely considering pairing these two devices:
>>
>> http://www.areca.us/products/html/products.htm
>>
>> That's an Areca 16 channel SATA II (I haven't even read up on what's new
>> in SATA II) RAID controller with an optional U320 SCSI daughter card to
>> connect to the host(s).
>
> I'm confused - SATA with a SCSI daughter card? Where does the SCSI go?

Bad ASCII diagram follows (D=disk, C=controller H=host):

    SATA   ____
D -------|    |  SCSI   ________
D -------| C  |--------|    H   |
D -------|    |        |________|
D -------|____|

(etc. up
to 16
drives)

The drives and the controller go in the Chenbro case.  U320 SCSI from the 
RAID controller in the Chenbro case to the 1U server.

C

From pgsql-performance-owner@postgresql.org  Sun Jan 15 00:05:03 2006
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From: Christopher Browne <cbbrowne@acm.org>
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Subject: Re: SAN/NAS options
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> Following up to myself again...
>
> On Wed, 14 Dec 2005, Charles Sprickman wrote:
>
>> Hello all,
>>
>> Supermicro 1U w/SCA backplane and 4 bays
>> 2x2.8 GHz Xeons
>> Adaptec 2015S "zero channel" RAID card
>
> I don't want to throw away the four machines like that that we have.
> I do want to throw away the ZCR cards... :)  If I ditch those I still
> have a 1U box with a U320 scsi plug on the back.
>
> I'm vaguely considering pairing these two devices:

> http://www.areca.us/products/html/products.htm
> http://www.chenbro.com.tw/Chenbro_Special/RM321.php

> How can I turn that box down?  Those people in the picture look very
> excited about it?  Seriously though, it looks like an interesting and
> economical pairing that gives me most of what I'm looking for:

The combination definitely looks attractive.  I have only been hearing
positive things about the Areca cards; the overall combination sounds
pretty attractive.

> Disadvantages:
>
> -only 1 or 2 hosts per box
> -more difficult to move storage from host to host (compared to a SAN
> or NAS system)
> -no fancy NetApp features like snapshots
> -I have no experience with Areca SATA->SCSI RAID controllers
>
> Any thoughts on this?  The controller looks to be about $1500, the
> enclosure about $400, and the drives are no great mystery, cost would
> depend on what total capacity I'm looking for.

Another "usage model" that could be appropriate would be
ATA-over-Ethernet...

<http://en.wikipedia.org/wiki/ATA-over-Ethernet>

> Our initial plan is to set one up for storage for a mail archive
> project, and to also have a host use this storage to host replicated
> copies of all Postgres databases.  If things look good, we'd start
> moving our main PG hosts to use a similar RAID box.

We're thinking about some stuff like this to host things that require
bulky amounts of disk that are otherwise "not high TPC" sorts of apps.
This is definitely not a "gold plated" answer, compared to the NetApp
and EMC boxes of the world, but can be useful in contexts where they
are too expensive.
-- 
let name="cbbrowne" and tld="gmail.com" in String.concat "@" [name;tld];;
http://linuxdatabases.info/info/x.html
It is usually a   good idea to  put  a capacitor of a  few microfarads
across the output, as shown.

From pgsql-performance-owner@postgresql.org  Sun Jan 15 13:21:13 2006
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Subject: Re: SAN/NAS options
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Charles Sprickman" <spork@bway.net>
cc: pgsql-performance@postgresql.org
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Charles,

On 1/14/06 7:23 PM, "Charles Sprickman" <spork@bway.net> wrote:

> The drives and the controller go in the Chenbro case.  U320 SCSI from the
> RAID controller in the Chenbro case to the 1U server.

Thanks for the explanation - I didn't click on your Areca link until now,
thinking it was a generic link to their products page.

Looks great - I think this might do better than the SATA -> FC products
because of the use of faster processors, but I'd keep my expectations low
until we see some performance data on it.

We've had some very poor experiences with Fibre Channel attach SATA disk
controllers.  A large vendor of same ultimately concluded that they will no
longer recommend them for database use because of the terrible performance
of their unit.  We ended up with a 110MB/s bottleneck on the controller when
using 200MB/s FC connections.

With the dual U320 attach and 16 drives, you should be able to saturate the
SCSI busses at about 600MB/s.  It would be great if you could post your I/O
results here!

- Luke



From pgsql-performance-owner@postgresql.org  Mon Jan 16 06:12:51 2006
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From: Alessandro Baretta <a.baretta@barettadeit.com>
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Subject: Suspending SELECTs 
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I am aware that what I am dreaming of is already available through cursors, but 
in a web application, cursors are bad boys, and should be avoided. What I would 
like to be able to do is to plan a query and run the plan to retreive a limited 
number of rows as well as the executor's state. This way, the burden of 
maintaining the cursor "on hold", between activations of the web resource which 
uses it, is transferred from the DBMS to the web application server, and, most 
importantly, the responsibility for garbage-collecting stale cursors is 
implicitely delegated to the garbage-collector of active user sessions. Without 
this mechanism, we are left with two equally unpleasant solutions: first, any 
time a user instantiates a new session, a new cursor would have to be declared 
for all relevant queries, and an ad-hoc garbage collection daemon would have to 
be written to periodically scan the database for stale cursors to be closed; 
otherwise, instead of using cursors, the web application could resort to 
OFFSET-LIMIT queries--no garbage collection issues but pathetic performance and 
server-load.

Do we have any way out?

Alex

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From pgsql-performance-owner@postgresql.org  Mon Jan 16 10:36:52 2006
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Subject: Materialized Views
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Hi,

I've been reading an interesting article which compared different 
database systems, focusing on materialized views. I was wondering how 
the postgresql developers feel about this feature ... is it planned to 
implement materialized views any time soon? They would greatly improve 
both performance and readability (and thus maintainability) of my code.

In particular I'm interested in a view which materializes whenever 
queried, and is invalidated as soon as underlying data is changed.

Mike

From pgsql-performance-owner@postgresql.org  Mon Jan 16 12:54:17 2006
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Subject: Use of * affect the performance
From: Marcos <mjs_ops@gmx.net>
To: pgsql-performance@postgresql.org
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Hi,

I always think that use of * in SELECT affected in the performance,
becoming the search slowest.

But I read in the a Postgres book's that it increases the speed of
search.

And now???? What the more fast?

Thanks


From pgsql-performance-owner@postgresql.org  Mon Jan 16 11:40:03 2006
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From: Frank Wiles <frank@wiles.org>
To: Michael Riess <mlriess@gmx.de>
Cc: pgsql-performance@postgresql.org
Subject: Re: Materialized Views
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On Mon, 16 Jan 2006 15:36:53 +0100
Michael Riess <mlriess@gmx.de> wrote:

> Hi,
> 
> I've been reading an interesting article which compared different 
> database systems, focusing on materialized views. I was wondering how 
> the postgresql developers feel about this feature ... is it planned
> to implement materialized views any time soon? They would greatly
> improve both performance and readability (and thus maintainability)
> of my code.
> 
> In particular I'm interested in a view which materializes whenever 
> queried, and is invalidated as soon as underlying data is changed.

  You can already build materialized views in PostgreSQL, but you
  end up doing the "heavy lifting" yourself with triggers. You put
  insert/update/delete triggers on the underlying tables of your
  view that "do the right thing" in your materialized view table.

  I wrote a blog entry about this recently,
  http://revsys.com/blog/archive/9, where I used a very simple
  materialized view to achieve the performance I needed. It has links
  to the relevant documentation you'll need however to build triggers
  for a more complex situation. 

  Hope this helps! 

 ---------------------------------
   Frank Wiles <frank@wiles.org>
   http://www.wiles.org
 ---------------------------------


From pgsql-performance-owner@postgresql.org  Mon Jan 16 12:18:09 2006
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hi mike

> In particular I'm interested in a view which materializes whenever 
> queried, and is invalidated as soon as underlying data is changed.

from the german pgsql list earlier last week:

http://jonathangardner.net/PostgreSQL/materialized_views/matviews.html

this seems to be pretty much what you want (except you'll have to update 
everything yourself). would be really nice if pgsql supports this "in-house"

cheers,
thomas 



From pgsql-performance-owner@postgresql.org  Mon Jan 16 12:27:06 2006
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Thanks!

Of course I know that I can build materialized views with triggers, but 
so far I've avoided using triggers altogether ... I would really 
appreciate something like "create view foo (select * from b) materialize 
on query".

But I'll look into your blog entry, thanks again!

Mike
> On Mon, 16 Jan 2006 15:36:53 +0100
> Michael Riess <mlriess@gmx.de> wrote:
> 
>> Hi,
>>
>> I've been reading an interesting article which compared different 
>> database systems, focusing on materialized views. I was wondering how 
>> the postgresql developers feel about this feature ... is it planned
>> to implement materialized views any time soon? They would greatly
>> improve both performance and readability (and thus maintainability)
>> of my code.
>>
>> In particular I'm interested in a view which materializes whenever 
>> queried, and is invalidated as soon as underlying data is changed.
> 
>   You can already build materialized views in PostgreSQL, but you
>   end up doing the "heavy lifting" yourself with triggers. You put
>   insert/update/delete triggers on the underlying tables of your
>   view that "do the right thing" in your materialized view table.
> 
>   I wrote a blog entry about this recently,
>   http://revsys.com/blog/archive/9, where I used a very simple
>   materialized view to achieve the performance I needed. It has links
>   to the relevant documentation you'll need however to build triggers
>   for a more complex situation. 
> 
>   Hope this helps! 
> 
>  ---------------------------------
>    Frank Wiles <frank@wiles.org>
>    http://www.wiles.org
>  ---------------------------------
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match
> 

From pgsql-performance-owner@postgresql.org  Mon Jan 16 13:51:57 2006
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To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs 
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Comments: In-reply-to Alessandro Baretta <a.baretta@barettadeit.com>
	message dated "Mon, 16 Jan 2006 11:13:00 +0100"
Date: Mon, 16 Jan 2006 12:51:47 -0500
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
> I am aware that what I am dreaming of is already available through
> cursors, but in a web application, cursors are bad boys, and should be
> avoided. What I would like to be able to do is to plan a query and run
> the plan to retreive a limited number of rows as well as the
> executor's state. This way, the burden of maintaining the cursor "on
> hold", between activations of the web resource which uses it, is
> transferred from the DBMS to the web application server,

This is a pipe dream, I'm afraid, as the state of a cursor does not
consist exclusively of bits that can be sent somewhere else and then
retrieved.  There are also locks to worry about, as well as the open
transaction itself, and these must stay alive inside the DBMS because
they affect the behavior of other transactions.  As an example, once
the cursor's originating transaction closes, there is nothing to stop
other transactions from modifying or removing rows it would have read.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 16 13:55:42 2006
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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alessandro Baretta <a.baretta@barettadeit.com>,
	pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
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Tom Lane wrote:
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
> > I am aware that what I am dreaming of is already available through
> > cursors, but in a web application, cursors are bad boys, and should be
> > avoided. What I would like to be able to do is to plan a query and run
> > the plan to retreive a limited number of rows as well as the
> > executor's state. This way, the burden of maintaining the cursor "on
> > hold", between activations of the web resource which uses it, is
> > transferred from the DBMS to the web application server,
> 
> This is a pipe dream, I'm afraid, as the state of a cursor does not
> consist exclusively of bits that can be sent somewhere else and then
> retrieved.

I wonder if we could have a way to "suspend" a transaction and restart
it later in another backend.  I think we could do something like this
using the 2PC machinery.

Not that I'm up for coding it; just an idea that crossed my mind.

-- 
Alvaro Herrera                           Developer, http://www.PostgreSQL.org
Oh, oh, las chicas galacianas, lo har�n por las perlas,
�Y las de Arrakis por el agua! Pero si buscas damas
Que se consuman como llamas, �Prueba una hija de Caladan! (Gurney Halleck)

From pgsql-performance-owner@postgresql.org  Mon Jan 16 14:10:52 2006
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Subject: Re: Suspending SELECTs 
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Date: Mon, 16 Jan 2006 13:10:38 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> I wonder if we could have a way to "suspend" a transaction and restart
> it later in another backend.  I think we could do something like this
> using the 2PC machinery.
> Not that I'm up for coding it; just an idea that crossed my mind.

It's not impossible, perhaps, but it would require an order-of-magnitude
expansion of the 2PC machinery --- the amount of state associated with
an open execution plan is daunting.  I think there are discussions about
this in the archives.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 16 14:45:19 2006
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Subject: Re: Suspending SELECTs
From: Mark Lewis <mark.lewis@mir3.com>
To: Alessandro Baretta <a.baretta@barettadeit.com>
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On Mon, 2006-01-16 at 11:13 +0100, Alessandro Baretta wrote:
> I am aware that what I am dreaming of is already available through cursors, but 
> in a web application, cursors are bad boys, and should be avoided. What I would 
> like to be able to do is to plan a query and run the plan to retreive a limited 
> number of rows as well as the executor's state. This way, the burden of 
> maintaining the cursor "on hold", between activations of the web resource which 
> uses it, is transferred from the DBMS to the web application server, and, most 
> importantly, the responsibility for garbage-collecting stale cursors is 
> implicitely delegated to the garbage-collector of active user sessions. Without 
> this mechanism, we are left with two equally unpleasant solutions: first, any 
> time a user instantiates a new session, a new cursor would have to be declared 
> for all relevant queries, and an ad-hoc garbage collection daemon would have to 
> be written to periodically scan the database for stale cursors to be closed; 
> otherwise, instead of using cursors, the web application could resort to 
> OFFSET-LIMIT queries--no garbage collection issues but pathetic performance and 
> server-load.
> 
> Do we have any way out?
> 
> Alex

I know that Tom has pretty much ruled out any persistent cursor
implementation in the database, but here's an idea for a workaround in
the app:

Have a pool of connections used for these queries.  When a user runs a
query the first time, create a cursor and remember that this user
session is associated with that particular connection.  When the user
tries to view the next page of results, request that particular
connection from the pool and continue to use the cursor.  Between
requests, this connection could of course be used to service other
users.

This avoids the awfulness of tying up a connection for the entire course
of a user session, but still allows you to use cursors for
performance.  

When a user session is invalidated or times out, you remove the mapping
for this connection and close the cursor.  Whenever there are no more
mappings for a particular connection, you can use the opportunity to
close the current transaction (to prevent eternal transactions).

If the site is at all busy, you will need to implement a pooling policy
such as 'do not open new cursors on the connection with the oldest
transaction', which will ensure that all transactions can be closed in a
finite amount of time, the upper bound on the duration of a transaction
is (longest_session_duration * connections in pool).

Limitations:

1. You shouldn't do anything that acquires write locks on the database
using these connections, because the transactions will be long-running.
To mitigate this, use a separate connection pool.

2. Doesn't work well if some queries take a long time to run, because
other users may need to wait for the connection, and another connection
won't do.

3. If this is a busy web site, you might end up with potentially many
thousands of open cursors.  I don't know if this introduces an
unacceptable performance penalty or other bottleneck in the server?

-- Mark Lewis

From pgsql-performance-owner@postgresql.org  Mon Jan 16 17:23:51 2006
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
>I am aware that what I am dreaming of is already available through
>cursors, but in a web application, cursors are bad boys, and should be
>avoided. What I would like to be able to do is to plan a query and run
>the plan to retreive a limited number of rows as well as the
>executor's state. This way, the burden of maintaining the cursor "on
>hold", between activations of the web resource which uses it, is
>transferred from the DBMS to the web application server,

I think you're trying to do something at the wrong layer of your architecture.  This task normally goes in your middleware layer, not your database layer.

There are several technologies that allow you to keep persistent database sessions open (for example, mod_perl, mod_cgi among others).  If you combine these with what's called "session affinity" (the ability of a load-balancing server to route a particular user back to the same persistent session object every time), then you can create a middleware layer that does exactly what you need.

Basically, you create a session object that holds all of the state (such as your cursor, and anything else you need to maintain between requests), and send back a cookie to the client.  Each time the client reconnects, your server finds the user's session object using the cookie, and you're ready to go.

The main trick is that you have to manage your session objects, primarily to flush the full state to the database, if too much time elapses between requests, and then be able to re-create them on demand.  Enterprise Java Beans has a large fraction of its design devoted to this sort of object management.

There are solutions for this in just about every middleware technology, from Apache/perl to EJB to CORBA.  Search for "session affinity" and you should find a lot of information.

Craig

From pgsql-performance-owner@postgresql.org  Mon Jan 16 17:54:03 2006
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From: "Qingqing Zhou" <zhouqq@cs.toronto.edu>
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Subject: Re: Use of * affect the performance
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"Marcos" <mjs_ops@gmx.net> wrote
>
> I always think that use of * in SELECT affected in the performance,
> becoming the search slowest.
>
> But I read in the a Postgres book's that it increases the speed of
> search.
>
> And now???? What the more fast?
>

If you mean use "*" vs. "explicitely name all columns of a relation", then 
there is almost no difference except the negligible difference in parsing. 
If you mean you just want part of the columns of a relation but you still 
use "*": Yes, you will save one projection operation for each result row but 
you will pay for more network traffic. In the worst case, say your "*" 
involves some toast attributes, you just hurt performance. Considering the 
benefits is so marginal and dangerous, I suggest stay with the idea that 
"only retrive the columns that you are interested in".

Regards,
Qingqing 



From pgsql-performance-owner@postgresql.org  Mon Jan 16 18:07:54 2006
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Date: Mon, 16 Jan 2006 23:07:52 +0100
From: Antoine <melser.anton@gmail.com>
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	:-(
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Hi,
We have a horribly designed postgres 8.1.0 database (not my fault!). I 
am pretty new to database design and management and have really no idea 
how to diagnose performance problems. The db has only 25-30 tables, and 
half of them are only there because our codebase needs them (long story, 
again not my fault!). Basically we have 10 tables that are being 
accessed, and only a couple of queries that join more than 3 tables. 
Most of the action takes place on two tables. One of the devs has done 
some truly atrocious coding and is using the db as his data access 
mechanism (instead of an in-memory array, and he only needs an 
array/collection).
It is running on an p4 3000ish (desktop model) running early linux 2.6 
(mdk 10.1) (512meg of ram) so that shouldn't be an issue, as we are 
talking only about 20000 inserts a day. It probably gets queried about 
20000 times a day too (all vb6 via the pg odbc).
So... seeing as I didn't really do any investigation as to setting 
default sizes for storage and the like - I am wondering whether our 
performance problems (a programme running 1.5x slower than two weeks 
ago) might not be coming from the db (or rather, my maintaining of it). 
I have turned on stats, so as to allow autovacuuming, but have no idea 
whether that could be related. Is it better to schedule a cron job to do 
it x times a day? I just left all the default values in postgres.conf... 
could I do some tweaking?
Does anyone know of any practical resources that might guide me in 
sorting out these sorts of problems? Some stuff with pratical examples 
would be good so I could compare with what we have.
Thanks
Antoine
ps. I had a look with top and it didn't look like it was going much over 
15% cpu, with memory usage negligeable. There are usually about 10 open 
connections. I couldn't find an easy way to check for disk accessings.
pps. The db is just one possible reason for our bottleneck so if you 
tell me it is very unlikely I will be most reassured!

From pgsql-performance-owner@postgresql.org  Mon Jan 16 18:42:53 2006
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On Mon, Jan 16, 2006 at 11:07:52PM +0100, Antoine wrote:

> performance problems (a programme running 1.5x slower than two weeks 
> ago) might not be coming from the db (or rather, my maintaining of it). 
> I have turned on stats, so as to allow autovacuuming, but have no idea 
> whether that could be related. Is it better to schedule a cron job to do 
> it x times a day? I just left all the default values in postgres.conf... 
> could I do some tweaking?

The first thing you need to do is find out where your problem is. 
Are queries running slowly?  You need to do some EXPLAIN ANALYSE
queries to understand that.

A


-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The whole tendency of modern prose is away from concreteness.
		--George Orwell

From pgsql-performance-owner@postgresql.org  Mon Jan 16 18:43:35 2006
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To: Antoine <melser.anton@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: new to postgres (and db management) and performance already a
	problem :-(
In-reply-to: <43CC1938.7020807@gmail.com> 
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Date: Mon, 16 Jan 2006 17:43:30 -0500
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Antoine <melser.anton@gmail.com> writes:
> So... seeing as I didn't really do any investigation as to setting 
> default sizes for storage and the like - I am wondering whether our 
> performance problems (a programme running 1.5x slower than two weeks 
> ago) might not be coming from the db (or rather, my maintaining of it). 

That does sound like a lack-of-vacuuming problem.  If the performance
goes back where it was after VACUUM FULL, then you can be pretty sure
of it.  Note that autovacuum is not designed to fix this for you: it
only ever issues regular vacuum not vacuum full.

> I couldn't find an easy way to check for disk accessings.

Watch the output of "vmstat 1" or "iostat 1" for info about that.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 16 18:48:27 2006
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> That does sound like a lack-of-vacuuming problem.  If the performance
> goes back where it was after VACUUM FULL, then you can be pretty sure
> of it.  Note that autovacuum is not designed to fix this for you: it
> only ever issues regular vacuum not vacuum full.

in our db system (for a website), i notice performance boosts after a vacuum 
full. but then, a VACUUM FULL takes 50min+ during which the db is not really 
accessible to web-users. is there another way to perform maintenance tasks 
AND leaving the db fully operable and accessible?

thanks,
thomas 



From pgsql-performance-owner@postgresql.org  Mon Jan 16 21:09:00 2006
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<me@alternize.com> writes:
> in our db system (for a website), i notice performance boosts after a vacuum 
> full. but then, a VACUUM FULL takes 50min+ during which the db is not really 
> accessible to web-users. is there another way to perform maintenance tasks 
> AND leaving the db fully operable and accessible?

You're not doing regular vacuums often enough.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 16 21:29:56 2006
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>> in our db system (for a website), i notice performance boosts after a 
>> vacuum
>> full. but then, a VACUUM FULL takes 50min+ during which the db is not 
>> really
>> accessible to web-users. is there another way to perform maintenance 
>> tasks
>> AND leaving the db fully operable and accessible?
>
> You're not doing regular vacuums often enough.

well, shouldn't autovacuum take care of "regular" vacuums? in addition to 
autovacuum, tables with data changes are vacuumed and reindexed once a day - 
still performance seems to degrade slowly until a vacuum full is 
initiated... could an additional daily vacuum over the entire db (even on 
tables that only get data added, never changed or removed) help?

- thomas 



From pgsql-performance-owner@postgresql.org  Tue Jan 17 00:02:59 2006
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>>> in our db system (for a website), i notice performance boosts after
>>> a vacuum
>>> full. but then, a VACUUM FULL takes 50min+ during which the db is
>>> not really
>>> accessible to web-users. is there another way to perform
>>> maintenance tasks
>>> AND leaving the db fully operable and accessible?
>>
>> You're not doing regular vacuums often enough.

By the way, you can get that VACUUM FULL to be "less injurious" if you
collect a list of tables:
pubs=# select table_schema, table_name from information_schema.tables
where table_type = 'BASE TABLE';

And then VACUUM FULL table by table.  It'll take the same 50 minutes;
it'll be more sporadically "unusable" which may turn out better.  But
that's just one step better; you want more steps :-).

> well, shouldn't autovacuum take care of "regular" vacuums? in addition
> to autovacuum, tables with data changes are vacuumed and reindexed
> once a day -
> still performance seems to degrade slowly until a vacuum full is
> initiated... could an additional daily vacuum over the entire db (even
> on tables that only get data added, never changed or removed) help?

Tables which never see updates/deletes don't need to get vacuumed very
often.  They should only need to get a periodic ANALYZE so that the
query optimizer gets the right stats.

There are probably many tables where pg_autovacuum is doing a fine
job.  What you need to do is to figure out which tables *aren't*
getting maintained well enough, and see about doing something special
to them.

What you may want to do is to go table by table and, for each one, do
two things:

1) VACUUM VERBOSE, which will report some information about how much
dead space there is on the table.

2) Contrib function pgstattuple(), which reports more detailed info
about space usage (alas, for just the table).

You'll find, between these, that there are some tables that have a LOT
of dead space.  At that point, there may be three answers:

a) PG 8.1 pg_autovacuum allows you to modify how often specific tables
are vacuumed; upping the numbers for the offending tables may clear
things up

b) Schedule cron jobs to periodically (hourly?  several times per
hour?) VACUUM the "offending" tables

c) You may decide to fall back to VACUUM FULL; if you do so just for a
small set of tables, the "time of pain" won't be the 50 minutes you're
living with now...

Try a), b), and c) in order on the "offending" tables as they address
the problem at increasing cost...
-- 
(reverse (concatenate 'string "moc.liamg" "@" "enworbbc"))
http://linuxdatabases.info/info/x.html
"Listen,  strange women, lyin'  in ponds,  distributin' swords,  is no
basis  for a  system of  government. Supreme  executive  power derives
itself from a mandate from  the masses, not from some farcical aquatic
ceremony."  -- Monty Python and the Holy Grail

From pgsql-performance-owner@postgresql.org  Tue Jan 17 00:13:27 2006
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	problem :-(
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> Try a), b), and c) in order on the "offending" tables as they address
> the problem at increasing cost...

thanks alot for the detailed information! the entire concept of vacuum isn't 
yet that clear to me, so your explanations and hints are very much 
appreciated. i'll defenitely try these steps this weekend when the next full 
vacuum was scheduled :-)

best regards,
thomas 



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On 17/01/06, me@alternize.com <me@alternize.com> wrote:
>
> > Try a), b), and c) in order on the "offending" tables as they address
> > the problem at increasing cost...
>
> thanks alot for the detailed information! the entire concept of vacuum
> isn't
> yet that clear to me, so your explanations and hints are very much
> appreciated. i'll defenitely try these steps this weekend when the next
> full
> vacuum was scheduled :-)


Thanks guys, that pretty much answered my question(s) too. I have a sneakin=
g
suspicion that vacuuming won't do too much for us however... now that I
think about it - we do very little removing, pretty much only inserts and
selects. I will give it a vacuum full and see what happens.
Cheers
Antoine




--
This is where I should put some witty comment.

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<br><br><div><span class=3D"gmail_quote">On 17/01/06, <b class=3D"gmail_sen=
dername"><a href=3D"mailto:me@alternize.com">me@alternize.com</a></b> &lt;<=
a href=3D"mailto:me@alternize.com">me@alternize.com</a>&gt; wrote:</span><b=
lockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, 20=
4, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
&gt; Try a), b), and c) in order on the &quot;offending&quot; tables as the=
y address<br>&gt; the problem at increasing cost...<br><br>thanks alot for =
the detailed information! the entire concept of vacuum isn't<br>yet that cl=
ear to me, so your explanations and hints are very much
<br>appreciated. i'll defenitely try these steps this weekend when the next=
 full<br>vacuum was scheduled :-)</blockquote><div><br>Thanks guys, that pr=
etty much answered my question(s) too. I have a sneaking suspicion that vac=
uuming won't do too much for us however... now that I think about it - we d=
o very little removing, pretty much only inserts and selects. I will give i=
t a vacuum full and see what happens.
<br>Cheers<br>Antoine <br></div><br></div><br><br clear=3D"all"><br>-- <br>=
This is where I should put some witty comment.

------=_Part_4473_31931275.1137485667200--

From pgsql-performance-owner@postgresql.org  Tue Jan 17 07:09:32 2006
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Subject: Use of Stored Procedures and
From: Marcos <mjs_ops@gmx.net>
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Hi,

I already read the documentation for to use the SPI_PREPARE and
SPI_EXEC... but sincerely I don't understand how I will use this
resource in my statements.

I looked for examples, but I din't good examples :(..

Somebody can help me?

Thanks.

Marcos.




From pgsql-performance-owner@postgresql.org  Tue Jan 17 06:19:03 2006
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hi,

I'm curious as to why autovacuum is not designed to do full vacuum. I 
know that the necessity of doing full vacuums can be reduced by 
increasing the FSM, but in my opinion that is the wrong decision for 
many applications. My application does not continuously 
insert/update/delete tuples at a constant rate. Basically there are long 
periods of relatively few modifications and short burst of high 
activity. Increasing the FSM so that even during these bursts most space 
  would be reused would mean to reduce the available memory for all 
other database tasks.

So my question is: What's the use of an autovacuum daemon if I still 
have to use a cron job to do full vacuums? wouldn't it just be a minor 
job to enhance autovacuum to be able to perform full vacuums, if one 
really wants it to do that - even if some developers think that it's the 
wrong approach?

Mike

From pgsql-performance-owner@postgresql.org  Tue Jan 17 06:29:40 2006
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Date: Tue, 17 Jan 2006 18:29:37 +0800
From: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
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> So my question is: What's the use of an autovacuum daemon if I still 
> have to use a cron job to do full vacuums? wouldn't it just be a minor 
> job to enhance autovacuum to be able to perform full vacuums, if one 
> really wants it to do that - even if some developers think that it's the 
> wrong approach?

You should never have to do full vacuums...

Chris

From pgsql-performance-owner@postgresql.org  Tue Jan 17 06:33:06 2006
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Hi,

did you read my post? In the first part I explained why I don't want to 
increase the FSM that much.

Mike

>> So my question is: What's the use of an autovacuum daemon if I still 
>> have to use a cron job to do full vacuums? wouldn't it just be a minor 
>> job to enhance autovacuum to be able to perform full vacuums, if one 
>> really wants it to do that - even if some developers think that it's 
>> the wrong approach?
> 
> You should never have to do full vacuums...
> 
> Chris
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
> 

From pgsql-performance-owner@postgresql.org  Tue Jan 17 07:35:23 2006
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Date: Tue, 17 Jan 2006 17:05:20 +0530
From: Pandurangan R S <pandurangan.r.s@gmail.com>
To: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
Subject: Re: Autovacuum / full vacuum
Cc: Michael Riess <mlriess@gmx.de>, pgsql-performance@postgresql.org
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>> You should never have to do full vacuums...

I would rather say, You should never have to do full vacuums by any
periodic means. It may be done on a adhoc basis, when you have figured
out that your table is never going to grow that big again.

On 1/17/06, Christopher Kings-Lynne <chriskl@familyhealth.com.au> wrote:
> > So my question is: What's the use of an autovacuum daemon if I still
> > have to use a cron job to do full vacuums? wouldn't it just be a minor
> > job to enhance autovacuum to be able to perform full vacuums, if one
> > really wants it to do that - even if some developers think that it's th=
e
> > wrong approach?
>
> You should never have to do full vacuums...
>
> Chris
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>

From pgsql-performance-owner@postgresql.org  Tue Jan 17 08:08:09 2006
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On Tue, Jan 17, 2006 at 11:33:02AM +0100, Michael Riess wrote:
>did you read my post? In the first part I explained why I don't want to 
>increase the FSM that much.

Since you didn't quantify it, that wasn't much of a data point. (IOW,
you'd generally have to be seriously resource constrained before the FSM
would be a significant source of memory consumption--in which case more
RAM would probably be a much better solution than screwing with
autovacuum.)

Mike Stone

From pgsql-performance-owner@postgresql.org  Tue Jan 17 09:17:41 2006
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Michael Riess wrote:
> hi,
> 
> I'm curious as to why autovacuum is not designed to do full vacuum.

Because a VACUUM FULL is too invasive.  Lazy vacuum is so light on the
system w.r.t. locks that it's generally not a problem to start one at
any time.  On the contrary, vacuum full could be a disaster on some
situations.

What's more, in general a lazy vacuum is enough to keep the dead space
within manageability, given a good autovacuum configuration and good FSM
configuration, so there's mostly no need for full vacuum.  (This is the
theory at least.)  For the situations where there is a need, we tell you
to issue it manually.

> So my question is: What's the use of an autovacuum daemon if I still 
> have to use a cron job to do full vacuums? wouldn't it just be a minor 
> job to enhance autovacuum to be able to perform full vacuums, if one 
> really wants it to do that - even if some developers think that it's the 
> wrong approach?

Yes, it is a minor job to "enhance" it to perform vacuum full.  The
problem is having a good approach to determining _when_ to issue a full
vacuum, and having a way to completely disallow it.  If you want to do
the development work, be my guest (but let us know your design first).
If you don't, I guess you would have to wait until it comes high enough
on someone's to-do list, maybe because you convinced him (or her, but we
don't have Postgres-ladies at the moment AFAIK) monetarily or something.

You can, of course, produce a patch and use it internally.  This is free
software, remember.

-- 
Alvaro Herrera                           Developer, http://www.PostgreSQL.org
"God is real, unless declared as int"

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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: new to postgres (and db management) and performance already a
	problem :-(
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On Tue, Jan 17, 2006 at 09:14:27AM +0100, Antoine wrote:
> think about it - we do very little removing, pretty much only inserts and
> selects. I will give it a vacuum full and see what happens.

UPDATES?  Remember that, in Postgres, UPDATE is effectively DELETE +
INSERT (from the point of view of storage, not the point of view of
the user).

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The plural of anecdote is not data.
		--Roger Brinner

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Hi, Tom,

Tom Lane wrote:

>>in our db system (for a website), i notice performance boosts after a vacuum 
>>full. but then, a VACUUM FULL takes 50min+ during which the db is not really 
>>accessible to web-users. is there another way to perform maintenance tasks 
>>AND leaving the db fully operable and accessible?
> 
> You're not doing regular vacuums often enough.

It may also help to increase the max_fsm_pages setting, so postmaster
has more memory to remember freed pages between VACUUMs.

HTH,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Tue Jan 17 09:53:00 2006
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Hi, Thomas,

me@alternize.com wrote:
>> Try a), b), and c) in order on the "offending" tables as they address
>> the problem at increasing cost...
> 
> thanks alot for the detailed information! the entire concept of vacuum
> isn't yet that clear to me, so your explanations and hints are very much
> appreciated. i'll defenitely try these steps this weekend when the next
> full vacuum was scheduled :-)

Basically, VACUUM scans the whole table and looks for pages containing
garbage rows (or row versions), deletes the garbage, and adds those
pages to the free space map (if there are free slots). When allocating
new rows / row versions, PostgreSQL first tries to fit them in pages
from the free space maps before allocating new pages. This is why a high
max_fsm_pages setting can help when VACUUM freqency is low.

VACUUM FULL additionally moves rows between pages, trying to concentrate
all the free space at the end of the tables (aka "defragmentation"), so
it can then truncate the files and release the space to the filesystem.

CLUSTER basically rebuilds the tables by copying all rows into a new
table, in index order, and then dropping the old table, which also
reduces fragmentation, but not as strong as VACUUM FULL might.

ANALYZE creates statistics about the distribution of values in a column,
allowing the query optimizer to estimate the selectivity of query criteria.

(This explanation is rather simplified, and ignores indices as well as
the fact that a table can consist of multiple files. Also, I believe
that newer PostgreSQL versions allow VACUUM to truncate files when free
pages happen to appear at the very end of the file.)


HTH,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:02:52 2006
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Subject: Re: Autovacuum / full vacuum
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> I'm curious as to why autovacuum is not designed to do full vacuum. 

Because that's terribly invasive due to the locks it takes out.

Lazy vacuum may chew some I/O, but it does *not* block your
application for the duration.

VACUUM FULL blocks the application.  That is NOT something that anyone
wants to throw into the "activity mix" randomly.
-- 
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From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:37:49 2006
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> did you read my post? In the first part I explained why I don't want
> to increase the FSM that much.

No, you didn't.  You explained *that* you thought you didn't want to
increase the FSM.  You didn't explain why.

FSM expansion comes fairly cheap, and tends to be an effective way of
eliminating the need for VACUUM FULL.  That is generally considered to
be a good tradeoff.  In future versions, there is likely to be more of
this sort of thing; for instance, on the ToDo list is a "Vacuum Space
Map" that would collect page IDs that need vacuuming so that
PostgreSQL could do "quicker" vacuums...
-- 
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From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:05:31 2006
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> VACUUM FULL blocks the application.  That is NOT something that anyone
> wants to throw into the "activity mix" randomly.

There must be a way to implement a daemon which frees up space of a 
relation without blocking it too long. It could abort after a certain 
number of blocks have been freed and then move to the next relation.

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:11:11 2006
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Michael Riess wrote:
> did you read my post? In the first part I explained why I don't want to 
> increase the FSM that much.

I'm sure he did, but just because you don't have enough FSM space to 
capture all everything from your "burst", that doesn't mean that space 
can't be reclaimed.  The next time a regular vacuum is run, it will once 
again try to fill the FSM with any remaining free space it finds in the 
table.  What normally happens is that your table will never bee 100% 
free of dead space, normally it will settle at some steady state size 
that is small percentage bigger than the table will be after a full 
vacuum.  As long as that percentage is small enough, the effect on 
performance is negligible.  Have you measured to see if things are truly 
faster after a VACUUM FULL?

Matt

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:30:20 2006
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To: "Matthew T. O'Connor" <matthew@zeut.net>
Cc: Michael Riess <mlriess@gmx.de>, pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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Hi, Matthew,

Matthew T. O'Connor wrote:

> I'm sure he did, but just because you don't have enough FSM space to
> capture all everything from your "burst", that doesn't mean that space
> can't be reclaimed.  The next time a regular vacuum is run, it will once
> again try to fill the FSM with any remaining free space it finds in the
> table.  What normally happens is that your table will never bee 100%
> free of dead space, normally it will settle at some steady state size
> that is small percentage bigger than the table will be after a full
> vacuum.  As long as that percentage is small enough, the effect on
> performance is negligible.

This will work if you've a steady stream of inserts / updates, but not
if you happen to have update bulks that exhaust the FSM capacity. The
update first fills up all the FSM, and then allocates new pages for the
rest. Then VACUUM comes and refills the FSM, however, the FSM does not
contain enough free space for the next large bulk update. The same is
for deletes and large bulk inserts, btw.

So your table keeps growing steadily, until VACUUM FULL or CLUSTER comes
along to clean up the mess.

Markus
-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:33:20 2006
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From: Michael Riess <mlriess@gmx.de>
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Subject: Re: Autovacuum / full vacuum
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Hi,

yes, some heavily used tables contain approx. 90% free space after a 
week. I'll try to increase FSM even more, but I think that I will still 
have to run a full vacuum every week. Prior to 8.1 I was using 7.4 and 
ran a full vacuum every day, so the autovacuum has helped a lot.

But actually I never understood why the database system slows down at 
all when there is much unused space in the files. Are the unused pages 
cached by the system, or is there another reason for the impact on the 
performance?

Mike


 >  Have you measured to see if things are truly
> faster after a VACUUM FULL?
> 
> Matt
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
> 

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:37:01 2006
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Subject: Re: Autovacuum / full vacuum
Date: Tue, 17 Jan 2006 08:36:53 -0600
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Thread-Topic: [PERFORM] Autovacuum / full vacuum
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From: "Larry Rosenman" <lrosenman@pervasive.com>
To: "Michael Riess" <mlriess@gmx.de>,
	<pgsql-performance@postgresql.org>
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Michael Riess wrote:
> Hi,
>=20
> yes, some heavily used tables contain approx. 90% free space after a
> week. I'll try to increase FSM even more, but I think that I will
> still have to run a full vacuum every week. Prior to 8.1 I was using
> 7.4 and ran a full vacuum every day, so the autovacuum has helped a
> lot.=20
>=20
> But actually I never understood why the database system slows down at
> all when there is much unused space in the files. Are the unused pages
> cached by the system, or is there another reason for the impact on the
> performance?

The reason is that the system needs to LOOK at the pages/tuples to see
if the tuples
are dead or not.=20

So, the number of dead tuples impacts the scans.

LER

>=20
> Mike
--=20
Larry Rosenman	=09
Database Support Engineer

PERVASIVE SOFTWARE. INC.
12365B RIATA TRACE PKWY
3015
AUSTIN TX  78727-6531=20

Tel: 512.231.6173
Fax: 512.231.6597
Email: Larry.Rosenman@pervasive.com
Web: www.pervasive.com=20

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:50:41 2006
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Subject: Re: Autovacuum / full vacuum
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Well,

I think that the documentation is not exactly easy to understand. I 
always wondered why there are no examples for common postgresql 
configurations. All I know is that the default configuration seems to be 
too low for production use. And while running postgres I get no hints as 
to which setting needs to be increased to improve performance. I have no 
chance to see if my FSM settings are too low other than to run vacuum 
full verbose in psql, pipe the result to a text file and grep for some 
words to get a somewhat comprehensive idea of how much unused space 
there is in my system.

Don't get me wrong - I really like PostgreSQL and it works well in my 
application. But somehow I feel that it might run much better ...

about the FSM: You say that increasing the FSM is fairly cheap - how 
should I know that?

>> did you read my post? In the first part I explained why I don't want
>> to increase the FSM that much.
> 
> No, you didn't.  You explained *that* you thought you didn't want to
> increase the FSM.  You didn't explain why.
> 
> FSM expansion comes fairly cheap  ...

From pgsql-performance-owner@postgresql.org  Tue Jan 17 10:56:56 2006
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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 11:18:59AM +0100, Michael Riess wrote:
> hi,
> 
> I'm curious as to why autovacuum is not designed to do full vacuum. I 

Because nothing that runs automatically should ever take an exclusive
lock on the entire database, which is what VACUUM FULL does.

> activity. Increasing the FSM so that even during these bursts most space 
>  would be reused would mean to reduce the available memory for all 
> other database tasks.

I don't believe the hit is enough that you should even notice it. 
You'd have to post some pretty incredible use cases to show that the
tiny loss of memory to FSM is worth (a) an exclusive lock and (b) the
loss of efficiency you get from having some preallocated pages in
tables.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The fact that technology doesn't work is no bar to success in the marketplace.
		--Philip Greenspun

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:04:44 2006
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Hi,

>> hi,
>>
>> I'm curious as to why autovacuum is not designed to do full vacuum. I 
> 
> Because nothing that runs automatically should ever take an exclusive
> lock on the entire database, which is what VACUUM FULL does.

I thought that vacuum full only locks the table which it currently 
operates on? I'm pretty sure that once a table has been vacuumed, it can 
be accessed without any restrictions while the vacuum process works on 
the next table.

> 
>> activity. Increasing the FSM so that even during these bursts most space 
>>  would be reused would mean to reduce the available memory for all 
>> other database tasks.
> 
> I don't believe the hit is enough that you should even notice it. 
> You'd have to post some pretty incredible use cases to show that the
> tiny loss of memory to FSM is worth (a) an exclusive lock and (b) the
> loss of efficiency you get from having some preallocated pages in
> tables.

I have 5000 tables and a workstation with 1 GB RAM which hosts an Apache 
   Web Server, Tomcat Servlet Container and PostgreSQL. RAM is not 
something that I have plenty of ... and the hardware is fixed and cannot 
be changed.



From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:07:34 2006
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Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 03:50:38PM +0100, Michael Riess wrote:
>about the FSM: You say that increasing the FSM is fairly cheap - how 
>should I know that?

Why would you assume otherwise, to the point of not considering changing
the setting? 

The documentation explains how much memory is used for FSM entries. If
you look at vacuum verbose output it will tell you how much memory
you're currently using for the FSM.

Mike Stone

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:08:01 2006
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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 03:50:38PM +0100, Michael Riess wrote:
> always wondered why there are no examples for common postgresql 
> configurations. 

You mean like this one? (for 8.0):

<http://www.powerpostgresql.com/Downloads/annotated_conf_80.html>



> All I know is that the default configuration seems to be 
> too low for production use. 

Define "production use".  It may be too low for you.

> chance to see if my FSM settings are too low other than to run vacuum 
> full verbose in psql, pipe the result to a text file and grep for some 

Not true.  You don't need a FULL on there to figure this out.

> about the FSM: You say that increasing the FSM is fairly cheap - how 
> should I know that?

Do the math.  The docs say this:

--snip---
max_fsm_pages (integer)

    Sets the maximum number of disk pages for which free space will
be tracked in the shared free-space map. Six bytes of shared memory
are consumed for each page slot. This setting must be more than 16 *
max_fsm_relations. The default is 20000. This option can only be set
at server start. 

max_fsm_relations (integer)

    Sets the maximum number of relations (tables and indexes) for
which free space will be tracked in the shared free-space map.
Roughly seventy bytes of shared memory are consumed for each slot.
The default is 1000. This option can only be set at server start. 

---snip---

So by default, you have 6 B * 20,000 = 120,000 bytes for the FSM pages.

By default, you have 70 B * 1,000 = 70,000 bytes for the FSM
relations.

Now, there are two knobs.  One of them tracks the number of
relations.  How many relations do you have?  Count the number of
indexes and tables you have, and give yourself some headroom in case
you add some more, and poof, you have your number for the relations.

Now all you need to do is figure out what your churn rate is on
tables, and count up how many disk pages that's likely to be.  Give
yourself a little headroom, and the number of FSM pages is done, too.

This churn rate is often tough to estimate, though, so you may have
to fiddle with it from time to time. 

A


-- 
Andrew Sullivan  | ajs@crankycanuck.ca
I remember when computers were frustrating because they *did* exactly what 
you told them to.  That actually seems sort of quaint now.
		--J.D. Baldwin

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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 09:09:02AM -0500, Matthew T. O'Connor wrote:
> vacuum.  As long as that percentage is small enough, the effect on 
> performance is negligible.  Have you measured to see if things are truly 

Actually, as long as the percentage is small enough and the pages are
really empty, the performance effect is positive.  If you have VACUUM
FULLed table, inserts have to extend the table before inserting,
whereas in a table with some space reclaimed, the I/O effect of
having to allocate another disk page is already done.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
When my information changes, I alter my conclusions.  What do you do sir?
		--attr. John Maynard Keynes

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:10:38 2006
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Date: Tue, 17 Jan 2006 16:10:34 +0100
From: hubert depesz lubaczewski <depesz@gmail.com>
To: Michael Riess <mlriess@gmx.de>
Subject: Re: Autovacuum / full vacuum
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On 1/17/06, Michael Riess <mlriess@gmx.de> wrote:
>
> about the FSM: You say that increasing the FSM is fairly cheap - how
> should I know that?
>

comment from original postgresql.conf file seems pretty obvious:
#max_fsm_pages =3D 20000          # min max_fsm_relations*16, 6 bytes each
#max_fsm_relations =3D 1000       # min 100, ~70 bytes each

basically setting max_fsm_pages to 1000000 consumes 6 megabytes. and i
definitelly doubt you will ever hit that high.

depesz

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On 1/17/06, <b class=3D"gmail_sendername">Michael Riess</b> &lt;<a href=3D"=
mailto:mlriess@gmx.de">mlriess@gmx.de</a>&gt; wrote:<div><span class=3D"gma=
il_quote"></span><blockquote class=3D"gmail_quote" style=3D"border-left: 1p=
x solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
about the FSM: You say that increasing the FSM is fairly cheap - how<br>sho=
uld I know that?<br></blockquote></div><br>comment from original postgresql=
.conf file seems pretty obvious:<br>#max_fsm_pages =3D 20000&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # min max_fsm_relations*16, 6 bytes=
 each
<br>#max_fsm_relations =3D 1000&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # min 1=
00, ~70 bytes each<br><br>basically setting max_fsm_pages to 1000000 consum=
es 6 megabytes. and i definitelly doubt you will ever hit that high.<br><br=
>depesz<br>

------=_Part_3919_18372093.1137510634749--

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:13:43 2006
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To: Michael Riess <mlriess@gmx.de>
cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum 
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Date: Tue, 17 Jan 2006 10:13:41 -0500
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Michael Riess <mlriess@gmx.de> writes:
> I'm curious as to why autovacuum is not designed to do full vacuum.

Locking considerations.  VACUUM FULL takes an exclusive lock, which
blocks any foreground transactions that want to touch the table ---
so it's really not the sort of thing you want being launched at
unpredictable times.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:13:57 2006
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Date: Tue, 17 Jan 2006 10:13:57 -0500
From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 03:05:29PM +0100, Michael Riess wrote:
> There must be a way to implement a daemon which frees up space of a 
> relation without blocking it too long. 

Define "too long".  If I have a table that needs to respond to a
SELECT in 50ms, I don't have time for you to lock my table.  If this
were such an easy thing to do, don't you think the folks who came up
wit the ingenious lazy vacuum system would have done it?

Remember, a vacuum full must completely lock the table, because it is
physically moving bits around on the disk.  So a SELECT can't happen
at the same time, because the bits might move out from under the
SELECT while it's running.  Concurrency is hard, and race conditions
are easy, to implement.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
A certain description of men are for getting out of debt, yet are
against all taxes for raising money to pay it off.
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From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:19:47 2006
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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 04:04:41PM +0100, Michael Riess wrote:
> 
> I thought that vacuum full only locks the table which it currently 
> operates on? I'm pretty sure that once a table has been vacuumed, it can 
> be accessed without any restrictions while the vacuum process works on 
> the next table.

Yes, I think the way I phrased it was unfortunate.  But if you issue
VACUUM FULL you'll get an exclusive lock on everything, although not
all at the same time.  But of course, if your query load is like
this

BEGIN;
SELECT from t1, t2 where t1.col1 = t2.col2;
[application logic]
UPDATE t3 . . .
COMMIT;

you'll find yourself blocked in the first statement on both t1 and
t2; and then on t3 as well.  You sure don't want that to happen
automagically, in the middle of your business day.  

> I have 5000 tables and a workstation with 1 GB RAM which hosts an Apache 
>   Web Server, Tomcat Servlet Container and PostgreSQL. RAM is not 
> something that I have plenty of ... and the hardware is fixed and cannot 
> be changed.

I see.  Well, I humbly submit that your problem is not the design of
the PostgreSQL server, then.  "The hardware is fixed and cannot be
changed," is the first optimisation I'd make.  Heck, I gave away a
box to charity only two weeks ago that would solve your problem
better than automatically issuing VACUUM FULL.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
Information security isn't a technological problem.  It's an economics
problem.
		--Bruce Schneier

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:36:13 2006
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To: Michael Riess <mlriess@gmx.de>
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Subject: Re: Autovacuum / full vacuum 
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Comments: In-reply-to Michael Riess <mlriess@gmx.de>
	message dated "Tue, 17 Jan 2006 15:33:18 +0100"
Date: Tue, 17 Jan 2006 10:36:11 -0500
Message-ID: <28618.1137512171@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Michael Riess <mlriess@gmx.de> writes:
> But actually I never understood why the database system slows down at 
> all when there is much unused space in the files.

Perhaps some of your common queries are doing sequential scans?  Those
would visit the empty pages as well as the full ones.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 17 11:59:33 2006
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Subject: Re: Autovacuum / full vacuum
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Andrew Sullivan <ajs@crankycanuck.ca>
Cc: pgsql-performance@postgresql.org
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On Tue, 2006-01-17 at 09:08, Andrew Sullivan wrote:
> On Tue, Jan 17, 2006 at 03:50:38PM +0100, Michael Riess wrote:
> > always wondered why there are no examples for common postgresql 
> > configurations. 
> 
> You mean like this one? (for 8.0):
> 
> <http://www.powerpostgresql.com/Downloads/annotated_conf_80.html>

I have to admit, looking at the documentation, that we really don't
explain this all that well in the administration section, and I can see
how easily led astray beginners are.

I think it's time I joined the pgsql-docs mailing list...

From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:04:09 2006
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From: Chris Browne <cbbrowne@acm.org>
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Subject: Re: Autovacuum / full vacuum
Date: Tue, 17 Jan 2006 11:43:14 -0500
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ajs@crankycanuck.ca (Andrew Sullivan) writes:
> On Tue, Jan 17, 2006 at 11:18:59AM +0100, Michael Riess wrote:
>> hi,
>> 
>> I'm curious as to why autovacuum is not designed to do full vacuum. I 
>
> Because nothing that runs automatically should ever take an exclusive
> lock on the entire database, which is what VACUUM FULL does.

That's a bit more than what autovacuum would probably do...
autovacuum does things table by table, so that what would be locked
should just be one table.

Even so, I'd not be keen on having anything that runs automatically
take an exclusive lock on even as much as a table.

>> activity. Increasing the FSM so that even during these bursts most
>> space would be reused would mean to reduce the available memory for
>> all other database tasks.
>
> I don't believe the hit is enough that you should even notice
> it. You'd have to post some pretty incredible use cases to show that
> the tiny loss of memory to FSM is worth (a) an exclusive lock and
> (b) the loss of efficiency you get from having some preallocated
> pages in tables.

There is *a* case for setting up full vacuums of *some* objects.  If
you have a table whose tuples all get modified in the course of some
common query, that will lead to a pretty conspicuous bloating of *that
table.*

Even with a big FSM, the pattern of how updates take place will lead
to that table having ~50% of its space being "dead/free," which is way
higher than the desirable "stable proportion" of 10-15%.

For that sort of table, it may be attractive to run VACUUM FULL on a
regular basis.  Of course, it may also be attractive to try to come up
with an update process that won't kill the whole table's contents at
once ;-).
-- 
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From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:07:56 2006
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Subject: sum of left join greater than its parts
From: Robert Treat <xzilla@users.sourceforge.net>
To: pgsql-performance@postgresql.org
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8.1.1, everything vacuumed/analyzed. basically i have two queries that
when executed individually run quite quickly, but if I try to left join
the second query onto the first, everything gets quite a bit slower. 

rms=# explain analyze
rms-#   SELECT
rms-#     software_download.*
rms-# FROM
rms-#         (
rms(#         SELECT
rms(#             host_id, max(mtime) as mtime
rms(#             FROM
rms(#             software_download
rms(#             WHERE
rms(#             bds_status_id not in (6,17,18)
rms(#             GROUP BY
rms(#             host_id, software_binary_id
rms(#          ) latest_download
rms-#          JOIN software_download using (host_id,mtime)
rms-#          JOIN software_binary b USING (software_binary_id)
rms-# WHERE
rms-#         binary_type_id IN (3,5,6);
                                                               QUERY PLAN                                                                
-----------------------------------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=870.00..992.56 rows=1 width=96) (actual time=90.566..125.782 rows=472 loops=1)
   Hash Cond: (("outer".host_id = "inner".host_id) AND ("outer"."?column2?" = "inner".mtime))
   ->  HashAggregate  (cost=475.88..495.32 rows=1555 width=16) (actual time=51.300..70.761 rows=10870 loops=1)
         ->  Seq Scan on software_download  (cost=0.00..377.78 rows=13080 width=16) (actual time=0.010..23.700 rows=13167 loops=1)
               Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
   ->  Hash  (cost=379.37..379.37 rows=2949 width=96) (actual time=39.167..39.167 rows=639 loops=1)
         ->  Hash Join  (cost=5.64..379.37 rows=2949 width=96) (actual time=0.185..37.808 rows=639 loops=1)
               Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
               ->  Seq Scan on software_download  (cost=0.00..277.16 rows=13416 width=96) (actual time=0.008..19.338 rows=13416 loops=1)
               ->  Hash  (cost=5.59..5.59 rows=20 width=4) (actual time=0.149..0.149 rows=22 loops=1)
                     ->  Seq Scan on software_binary b  (cost=0.00..5.59 rows=20 width=4) (actual time=0.011..0.108 rows=22 loops=1)
                           Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
 Total runtime: 126.704 ms
(13 rows)


rms=# explain analyze 
rms-# SELECT
rms-#                                 entityid, rmsbinaryid, rmsbinaryid as software_binary_id, timestamp as downloaded, ia.host_id
rms-#                         FROM
rms-#                                 (SELECT
rms(#                                         entityid, rmsbinaryid,max(msgid) as msgid
rms(#                                 FROM
rms(#                                         msg306u
rms(#                                 WHERE
rms(#                                         downloadstatus=1
rms(#                                 GROUP BY entityid,rmsbinaryid
rms(#                                 ) a1
rms-#                                 JOIN myapp_app ia on (entityid=myapp_app_id)
rms-#                                 JOIN
rms-#                                         (SELECT *
rms(#                                         FROM msg306u
rms(#                                         WHERE
rms(#                                         downloadstatus != 0
rms(#                                         ) a2 USING(entityid,rmsbinaryid,msgid)
rms-# ;
                                                                    QUERY PLAN                                                                     
---------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=1733.79..4620.38 rows=1 width=20) (actual time=81.160..89.826 rows=238 loops=1)
   ->  Nested Loop  (cost=1733.79..4615.92 rows=1 width=20) (actual time=81.142..86.826 rows=238 loops=1)
         Join Filter: ("outer".rmsbinaryid = "inner".rmsbinaryid)
         ->  HashAggregate  (cost=1733.79..1740.92 rows=570 width=12) (actual time=81.105..81.839 rows=323 loops=1)
               ->  Bitmap Heap Scan on msg306u  (cost=111.75..1540.65 rows=25752 width=12) (actual time=4.490..41.233 rows=25542 loops=1)
                     ->  Bitmap Index Scan on rht3  (cost=0.00..111.75 rows=25752 width=0) (actual time=4.248..4.248 rows=25542 loops=1)
         ->  Index Scan using msg306u_entityid_msgid_idx on msg306u  (cost=0.00..5.02 rows=1 width=20) (actual time=0.008..0.010 rows=1 loops=323)
               Index Cond: (("outer".entityid = msg306u.entityid) AND ("outer"."?column3?" = msg306u.msgid))
               Filter: (downloadstatus <> '0'::text)
   ->  Index Scan using myapp_app_pkey on myapp_app ia  (cost=0.00..4.44 rows=1 width=8) (actual time=0.006..0.007 rows=1 loops=238)
         Index Cond: ("outer".entityid = ia.myapp_app_id)
 Total runtime: 90.270 ms
(12 rows)


and here are the two queries left joined together. 

rms=# explain analyze
rms-# select * from   (
rms(#              SELECT
rms(#     software_download.*
rms(# FROM
rms(#         (
rms(#         SELECT
rms(#             host_id, max(mtime) as mtime
rms(#             FROM
rms(#             software_download
rms(#             WHERE
rms(#             bds_status_id not in (6,17,18)
rms(#             GROUP BY
rms(#             host_id, software_binary_id
rms(#          ) latest_download
rms(#          JOIN software_download using (host_id,mtime)
rms(#          JOIN software_binary b USING (software_binary_id)
rms(# WHERE
rms(#         binary_type_id IN (3,5,6)
rms(# ) ld
rms-#       LEFT JOIN
rms-#                         (SELECT
rms(#                                 entityid, rmsbinaryid, rmsbinaryid as software_binary_id, timestamp as downloaded, ia.host_id
rms(#                         FROM
rms(#                                 (SELECT
rms(#                                         entityid, rmsbinaryid,max(msgid) as msgid
rms(#                                 FROM
rms(#                                         msg306u
rms(#                                 WHERE
rms(#                                         downloadstatus=1
rms(#                                 GROUP BY entityid,rmsbinaryid
rms(#                                 ) a1
rms(#                                 JOIN myapp_app ia on (entityid=myapp_app_id)
rms(#                                 JOIN
rms(#                                         (SELECT *
rms(#                                         FROM msg306u
rms(#                                         WHERE
rms(#                                         downloadstatus != 0
rms(#                                         ) a2 USING(entityid,rmsbinaryid,msgid)
rms(#                         ) aa USING (host_id,software_binary_id);
                                                                         QUERY PLAN                                                                         
------------------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop Left Join  (cost=2603.79..5612.95 rows=1 width=112) (actual time=181.988..4359.330 rows=472 loops=1)
   Join Filter: (("outer".host_id = "inner".host_id) AND ("outer".software_binary_id = "inner".rmsbinaryid))
   ->  Hash Join  (cost=870.00..992.56 rows=1 width=96) (actual time=92.048..131.154 rows=472 loops=1)
         Hash Cond: (("outer".host_id = "inner".host_id) AND ("outer"."?column2?" = "inner".mtime))
         ->  HashAggregate  (cost=475.88..495.32 rows=1555 width=16) (actual time=52.302..73.892 rows=10870 loops=1)
               ->  Seq Scan on software_download  (cost=0.00..377.78 rows=13080 width=16) (actual time=0.010..24.181 rows=13167 loops=1)
                     Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
         ->  Hash  (cost=379.37..379.37 rows=2949 width=96) (actual time=39.645..39.645 rows=639 loops=1)
               ->  Hash Join  (cost=5.64..379.37 rows=2949 width=96) (actual time=0.187..38.265 rows=639 loops=1)
                     Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
                     ->  Seq Scan on software_download  (cost=0.00..277.16 rows=13416 width=96) (actual time=0.008..19.905 rows=13416 loops=1)
                     ->  Hash  (cost=5.59..5.59 rows=20 width=4) (actual time=0.151..0.151 rows=22 loops=1)
                           ->  Seq Scan on software_binary b  (cost=0.00..5.59 rows=20 width=4) (actual time=0.011..0.109 rows=22 loops=1)
                                 Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
   ->  Nested Loop  (cost=1733.79..4620.38 rows=1 width=20) (actual time=0.196..8.620 rows=238 loops=472)
         ->  Nested Loop  (cost=1733.79..4615.92 rows=1 width=16) (actual time=0.186..5.702 rows=238 loops=472)
               Join Filter: ("outer".rmsbinaryid = "inner".rmsbinaryid)
               ->  HashAggregate  (cost=1733.79..1740.92 rows=570 width=12) (actual time=0.173..0.886 rows=323 loops=472)
                     ->  Bitmap Heap Scan on msg306u  (cost=111.75..1540.65 rows=25752 width=12) (actual time=4.372..41.248 rows=25542 loops=1)
                           ->  Bitmap Index Scan on rht3  (cost=0.00..111.75 rows=25752 width=0) (actual time=4.129..4.129 rows=25542 loops=1)
               ->  Index Scan using msg306u_entityid_msgid_idx on msg306u  (cost=0.00..5.02 rows=1 width=20) (actual time=0.008..0.010 rows=1 loops=152456)
                     Index Cond: (("outer".entityid = msg306u.entityid) AND ("outer"."?column3?" = msg306u.msgid))
                     Filter: (downloadstatus <> '0'::text)
         ->  Index Scan using myapp_app_pkey on myapp_app ia  (cost=0.00..4.44 rows=1 width=8) (actual time=0.005..0.007 rows=1 loops=112336)
               Index Cond: ("outer".entityid = ia.myapp_app_id)
 Total runtime: 4360.552 ms
(26 rows)

istm this query should be able to return quite a bit faster, and setting
enable_nestloop = off seems to back up this theory:


rms=# explain analyze
rms-#  select * from   (
rms(#               SELECT
rms(#      software_download.*
rms(#  FROM
rms(#          (
rms(#          SELECT
rms(#              host_id, max(mtime) as mtime
rms(#              FROM
rms(#              software_download
rms(#              WHERE
rms(#              bds_status_id not in (6,17,18)
rms(#              GROUP BY
rms(#              host_id, software_binary_id
rms(#           ) latest_download
rms(#           JOIN software_download using (host_id,mtime)
rms(#           JOIN software_binary b USING (software_binary_id)
rms(#  WHERE
rms(#          binary_type_id IN (3,5,6)
rms(#                  ) ld
rms-#                  LEFT JOIN
rms-#                          (SELECT
rms(#                                  entityid, rmsbinaryid, rmsbinaryid as software_binary_id, timestamp as downloaded, ia.host_id
rms(#                          FROM
rms(#                                  (SELECT
rms(#                                          entityid, rmsbinaryid,max(msgid) as msgid
rms(#                                  FROM
rms(#                                          msg306u
rms(#                                  WHERE
rms(#                                          downloadstatus=1
rms(#                                  GROUP BY entityid,rmsbinaryid
rms(#                                  ) a1
rms(#                                  JOIN myapp_app ia on (entityid=myapp_app_id)
rms(#                                  JOIN
rms(#                                          (SELECT *
rms(#                                          FROM msg306u
rms(#                                          WHERE
rms(#                                          downloadstatus != 0
rms(#                                          ) a2 USING(entityid,rmsbinaryid,msgid)
rms(#                          ) aa USING (host_id,software_binary_id);
                                                                         QUERY PLAN                                                                         
------------------------------------------------------------------------------------------------------------------------------------------------------------
 Hash Left Join  (cost=6976.52..7099.10 rows=1 width=112) (actual time=500.681..537.894 rows=472 loops=1)
   Hash Cond: (("outer".host_id = "inner".host_id) AND ("outer".software_binary_id = "inner".rmsbinaryid))
   ->  Hash Join  (cost=870.00..992.56 rows=1 width=96) (actual time=91.738..127.423 rows=472 loops=1)
         Hash Cond: (("outer".host_id = "inner".host_id) AND ("outer"."?column2?" = "inner".mtime))
         ->  HashAggregate  (cost=475.88..495.32 rows=1555 width=16) (actual time=52.025..71.872 rows=10870 loops=1)
               ->  Seq Scan on software_download  (cost=0.00..377.78 rows=13080 width=16) (actual time=0.009..23.959 rows=13167 loops=1)
                     Filter: ((bds_status_id <> 6) AND (bds_status_id <> 17) AND (bds_status_id <> 18))
         ->  Hash  (cost=379.37..379.37 rows=2949 width=96) (actual time=39.612..39.612 rows=639 loops=1)
               ->  Hash Join  (cost=5.64..379.37 rows=2949 width=96) (actual time=0.183..38.220 rows=639 loops=1)
                     Hash Cond: ("outer".software_binary_id = "inner".software_binary_id)
                     ->  Seq Scan on software_download  (cost=0.00..277.16 rows=13416 width=96) (actual time=0.008..19.511 rows=13416 loops=1)
                     ->  Hash  (cost=5.59..5.59 rows=20 width=4) (actual time=0.147..0.147 rows=22 loops=1)
                           ->  Seq Scan on software_binary b  (cost=0.00..5.59 rows=20 width=4) (actual time=0.011..0.108 rows=22 loops=1)
                                 Filter: ((binary_type_id = 3) OR (binary_type_id = 5) OR (binary_type_id = 6))
   ->  Hash  (cost=6106.52..6106.52 rows=1 width=20) (actual time=408.915..408.915 rows=238 loops=1)
         ->  Merge Join  (cost=5843.29..6106.52 rows=1 width=20) (actual time=338.516..408.477 rows=238 loops=1)
               Merge Cond: (("outer".rmsbinaryid = "inner".rmsbinaryid) AND ("outer".msgid = "inner".msgid) AND ("outer".entityid = "inner".entityid))
               ->  Sort  (cost=1857.37..1858.80 rows=570 width=16) (actual time=88.816..89.179 rows=323 loops=1)
                     Sort Key: a1.rmsbinaryid, a1.msgid, a1.entityid
                     ->  Hash Join  (cost=1793.98..1831.28 rows=570 width=16) (actual time=86.452..88.074 rows=323 loops=1)
                           Hash Cond: ("outer".entityid = "inner".myapp_app_id)
                           ->  HashAggregate  (cost=1733.79..1740.92 rows=570 width=12) (actual time=80.772..81.320 rows=323 loops=1)
                                 ->  Bitmap Heap Scan on msg306u  (cost=111.75..1540.65 rows=25752 width=12) (actual time=4.515..40.984 rows=25542 loops=1)
                                       ->  Bitmap Index Scan on rht3  (cost=0.00..111.75 rows=25752 width=0) (actual time=4.271..4.271 rows=25542 loops=1)
                           ->  Hash  (cost=55.95..55.95 rows=1695 width=8) (actual time=5.663..5.663 rows=1695 loops=1)
                                 ->  Seq Scan on myapp_app ia  (cost=0.00..55.95 rows=1695 width=8) (actual time=0.006..2.888 rows=1695 loops=1)
               ->  Sort  (cost=3985.92..4050.30 rows=25752 width=20) (actual time=249.682..286.295 rows=25542 loops=1)
                     Sort Key: public.msg306u.rmsbinaryid, public.msg306u.msgid, public.msg306u.entityid
                     ->  Seq Scan on msg306u  (cost=0.00..1797.28 rows=25752 width=20) (actual time=0.010..80.572 rows=25542 loops=1)
                           Filter: (downloadstatus <> '0'::text)
 Total runtime: 540.284 ms
(31 rows)

i've been banging on this one off and on for awhile now with little
progress, can someone explain why it is choosing the initial slower plan
and/or how to get it to run something closer to the second faster plan?


Robert Treat
-- 
Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL


From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:17:03 2006
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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 09:59:25AM -0600, Scott Marlowe wrote:
> I have to admit, looking at the documentation, that we really don't
> explain this all that well in the administration section, and I can see
> how easily led astray beginners are.

I understand what you mean, but I suppose my reaction would be that
what we really need is a place to keep these things, with a note in
the docs that the "best practice" settings for these are documented
at <some url>, and evolve over time as people gain expertise with the
new features.

I suspect, for instance, that nobody knows exactly the right settings
for any generic workload yet under 8.1 (although probably people know
them well enough for particular workloads).

A


-- 
Andrew Sullivan  | ajs@crankycanuck.ca
This work was visionary and imaginative, and goes to show that visionary
and imaginative work need not end up well. 
		--Dennis Ritchie

From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:25:14 2006
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Subject: Re: Autovacuum / full vacuum
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Hi, Michael,

Michael Riess wrote:

> But actually I never understood why the database system slows down at
> all when there is much unused space in the files. Are the unused pages
> cached by the system, or is there another reason for the impact on the
> performance?

No, they are not cached as such, but PostgreSQL caches whole pages, and
you don't have only empty pages, but also lots of partially empty pages,
so the signal/noise ratio is worse (means PostgreSQL has to fetch more
pages to get the same data).

Sequential scans etc. are also slower.

And some file systems get slower when files get bigger or there are more
files, but this effect should not really be noticeable here.

HTH,
Markus


-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:28:35 2006
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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Chris Browne <cbbrowne@acm.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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Chris Browne wrote:
> ajs@crankycanuck.ca (Andrew Sullivan) writes:
> > On Tue, Jan 17, 2006 at 11:18:59AM +0100, Michael Riess wrote:
> >> hi,
> >> 
> >> I'm curious as to why autovacuum is not designed to do full vacuum. I 
> >
> > Because nothing that runs automatically should ever take an exclusive
> > lock on the entire database, which is what VACUUM FULL does.
> 
> That's a bit more than what autovacuum would probably do...
> autovacuum does things table by table, so that what would be locked
> should just be one table.

Even a database-wide vacuum does not take locks on more than one table.
The table locks are acquired and released one by one, as the operation
proceeds.  And as you know, autovacuum (both 8.1's and contrib) does
issue database-wide vacuums, if it finds a database close to an xid
wraparound.

-- 
Alvaro Herrera                        http://www.advogato.org/person/alvherre
"Las mujeres son como hondas:  mientras m�s resistencia tienen,
 m�s lejos puedes llegar con ellas"  (Jonas Nightingale, Leap of Faith)

From pgsql-performance-owner@postgresql.org  Tue Jan 17 13:31:47 2006
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Subject: Re: Autovacuum / full vacuum
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Andrew Sullivan <ajs@crankycanuck.ca>
Cc: pgsql-performance@postgresql.org
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On Tue, 2006-01-17 at 11:16, Andrew Sullivan wrote:
> On Tue, Jan 17, 2006 at 09:59:25AM -0600, Scott Marlowe wrote:
> > I have to admit, looking at the documentation, that we really don't
> > explain this all that well in the administration section, and I can see
> > how easily led astray beginners are.
> 
> I understand what you mean, but I suppose my reaction would be that
> what we really need is a place to keep these things, with a note in
> the docs that the "best practice" settings for these are documented
> at <some url>, and evolve over time as people gain expertise with the
> new features.
> 
> I suspect, for instance, that nobody knows exactly the right settings
> for any generic workload yet under 8.1 (although probably people know
> them well enough for particular workloads).

But the problem is bigger than that.  The administrative docs were
obviously evolved over time, and now they kind of jump around and around
covering the same subject from different angles and at different
depths.  Even I find it hard to find what I need, and I know PostgreSQL
administration well enough to be pretty darned good at it.

For the beginner, it must seem much more confusing.  The more I look at
the administration section of the docs, the more I want to reorganize
the whole thing, and rewrite large sections of it as well.

From pgsql-performance-owner@postgresql.org  Tue Jan 17 14:13:54 2006
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From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 11:43:14AM -0500, Chris Browne wrote:
> ajs@crankycanuck.ca (Andrew Sullivan) writes:
> > Because nothing that runs automatically should ever take an exclusive
> > lock on the entire database, 

> That's a bit more than what autovacuum would probably do...

Or even VACUUM FULL, as I tried to make clearer in another message:
the way I phrased it suggests that it's a simultaneous lock on the
entire database (when it is most certainly not).  I didn't intend to
mislead; my apologies.

Note, though, that the actual effect for a user might look worse
than a lock on the entire database, though, if you conider
statement_timeout and certain use patterns.

Suppose you want to issue occasional VACCUM FULLs, but your
application is prepared for this, and depends on statement_timeout to
tell it "sorry, too long, try again".  Now, if the exclusive lock on
any given table takes less than statement_timeout, so that each
statement is able to continue in its time, the application looks like
it's having an outage _even though_ it is actually blocked on
vacuums.  (Yes, it's poor application design.  There's plenty of that
in the world, and you can't always fix it.)

> There is *a* case for setting up full vacuums of *some* objects.  If
> you have a table whose tuples all get modified in the course of some
> common query, that will lead to a pretty conspicuous bloating of *that
> table.*

Sure.  And depending on your use model, that might be good.  In many
cases, though, a "rotor table + view + truncate" approach would be
better, and would allow improved uptime.  If you don't care about
uptime, and can take long outages every day, then the discussion is
sort of moot anyway.  And _all_ of this is moot, as near as I can
tell, given the OP's claim that the hardware is adequate and
immutable, even though the former claim is demonstrably false.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The fact that technology doesn't work is no bar to success in the marketplace.
		--Philip Greenspun

From pgsql-performance-owner@postgresql.org  Tue Jan 17 15:04:11 2006
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alvherre@alvh.no-ip.org (Alvaro Herrera) writes:
> Chris Browne wrote:
>> ajs@crankycanuck.ca (Andrew Sullivan) writes:
>> > On Tue, Jan 17, 2006 at 11:18:59AM +0100, Michael Riess wrote:
>> >> hi,
>> >> 
>> >> I'm curious as to why autovacuum is not designed to do full vacuum. I 
>> >
>> > Because nothing that runs automatically should ever take an exclusive
>> > lock on the entire database, which is what VACUUM FULL does.
>> 
>> That's a bit more than what autovacuum would probably do...
>> autovacuum does things table by table, so that what would be locked
>> should just be one table.
>
> Even a database-wide vacuum does not take locks on more than one table.
> The table locks are acquired and released one by one, as the operation
> proceeds.  And as you know, autovacuum (both 8.1's and contrib) does
> issue database-wide vacuums, if it finds a database close to an xid
> wraparound.

Has that changed recently?  I have always seen "vacuumdb" or SQL
"VACUUM" (without table specifications) running as one long
transaction which doesn't release the locks that it is granted until
the end of the transaction.
-- 
"cbbrowne","@","acm.org"
http://cbbrowne.com/info/spiritual.html
"My nostalgia for Icon makes me forget about any of the bad things.  I
don't have much nostalgia for Perl, so its faults I remember."
-- Scott Gilbert comp.lang.python

From pgsql-performance-owner@postgresql.org  Tue Jan 17 15:32:59 2006
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To: Chris Browne <cbbrowne@acm.org>
cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum 
In-reply-to: <604q42elzl.fsf@dba2.int.libertyrms.com> 
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Date: Tue, 17 Jan 2006 14:32:52 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Chris Browne <cbbrowne@acm.org> writes:
> alvherre@alvh.no-ip.org (Alvaro Herrera) writes:
>> Even a database-wide vacuum does not take locks on more than one table.
>> The table locks are acquired and released one by one, as the operation
>> proceeds.

> Has that changed recently?  I have always seen "vacuumdb" or SQL
> "VACUUM" (without table specifications) running as one long
> transaction which doesn't release the locks that it is granted until
> the end of the transaction.

You sure?  It's not supposed to, and watching a database-wide vacuum
with "select * from pg_locks" doesn't look to me like it ever has locks
on more than one table (plus the table's indexes and toast table).

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 17 15:55:50 2006
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Date: Tue, 17 Jan 2006 20:56:00 +0100
From: Alessandro Baretta <a.baretta@barettadeit.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
References: <43CB71AC.20203@barettadeit.com> <9766.1137433907@sss.pgh.pa.us>
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Tom Lane wrote:
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
> 
>>I am aware that what I am dreaming of is already available through
>>cursors, but in a web application, cursors are bad boys, and should be
>>avoided. What I would like to be able to do is to plan a query and run
>>the plan to retreive a limited number of rows as well as the
>>executor's state. This way, the burden of maintaining the cursor "on
>>hold", between activations of the web resource which uses it, is
>>transferred from the DBMS to the web application server,
> 
> 
> This is a pipe dream, I'm afraid, as the state of a cursor does not
> consist exclusively of bits that can be sent somewhere else and then
> retrieved.  There are also locks to worry about, as well as the open
> transaction itself, and these must stay alive inside the DBMS because
> they affect the behavior of other transactions.  As an example, once
> the cursor's originating transaction closes, there is nothing to stop
> other transactions from modifying or removing rows it would have read.

I understand most of these issues, and expected this kind of reply. Please, 
allow me to insist that we reason on this problem and try to find a solution. My 
reason for doing so is that the future software industry is likely to see more 
and more web applications retrieving data from virtually endless databases, and 
in such contexts, it is sensible to ask the final client--the web client--to 
store the "cursor state", because web interaction is intrinsically asynchronous, 
and you cannot count on users logging out when they're done, releasing resources 
allocated to them. Think of Google.

Let me propose a possible solution strategy for the problem of "client-side 
cursors".
* Let us admit the limitation that a "client-side cursor" can only be declared 
in a transaction where no inserts, updates or deletes are allowed, so that such 
a transaction is virtually non-existent to other transactions. This allows the 
backend to close the transaction and release locks as soon as the cursor is 
declared.
* When the cursor state is pushed back to the backend, no new transaction is 
instantiated, but the XID of the original transaction is reused. In the MVCC 
system, this allows us to achieve a perfectly consistent view of the database at 
the instant the original transaction started, unless a VACUUM command has been 
executed in the meantime, in which case I would lose track of tuples which would 
have been live in the context of the original transaction, but have been updated 
or deleted and later vacuumed; however, this does not bother me at all.

Is this not a viable solution?

Alex

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From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:14:22 2006
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Date: Tue, 17 Jan 2006 15:00:37 -0500
From: Yantao Shi <y.shi@larc.nasa.gov>
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Subject: wildcard search performance with "like"
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Hi,

I have a postges 8.1.1 table with over 29 million rows in it. The colunm 
(file_name) that I need to search on has entries like the following:

 MOD04_L2.A2005311.1400.004.2005312013848.hdf                                                        

 MYD04_L2.A2005311.0700.004.2005312013437.hdf                     

I have an index on this column. But an index search is performance only 
when I give the full file_name for search:

testdbspc=# explain select file_name from catalog where file_name = 
'MOD04_L2.A2005311.1400.004.2005312013848.hdf';
QUERY PLAN
Index Scan using catalog_pk_idx on catalog  (cost=0.00..6.01 rows=1 
width=404)
  Index Cond: (file_name = 
'MOD04_L2.A2005311.1400.004.2005312013848.hdf'::bpchar)
(2 rows)

What I really need to do most of the time is a multi-wildcard search on 
this column, which is now doing a whole table scan without using the 
index at all:

testdbspc=# explain select file_name from catalog where file_name like 
'MOD04_L2.A2005311.%.004.2005312013%.hdf';
QUERY PLAN
Seq Scan on catalog  (cost=0.00..429.00 rows=1 width=404)
  Filter: (file_name ~~ 'MOD04_L2.A2005311.%.004.2005312013%.hdf'::text)
(2 rows)

Obviously, the performance of the table scan on such a large table is 
not acceptable.

I tried full-text indexing and searching. It did NOT work on this column 
because all the letters and numbers are linked together with "." and 
considered one big single word by to_tsvector.

Any solutions for this column to use an index search with multiple wild 
cards?

Thanks a lot,
Yantao Shi




From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:04:46 2006
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From: Michael Stone <mstone+postgres@mathom.us>
Subject: Re: Suspending SELECTs
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On Tue, Jan 17, 2006 at 08:56:00PM +0100, Alessandro Baretta wrote:
>I understand most of these issues, and expected this kind of reply. Please, 
>allow me to insist that we reason on this problem and try to find a 
>solution. My reason for doing so is that the future software industry is 
>likely to see more and more web applications retrieving data from virtually 
>endless databases, and in such contexts, it is sensible to ask the final 
>client--the web client--to store the "cursor state", because web 
>interaction is intrinsically asynchronous, and you cannot count on users 
>logging out when they're done, releasing resources allocated to them. Think 
>of Google.

I don't understand why it is better to rework the db instead of just
having the web middleware keep track of what cursors are associated with
what sessions?

Mike Stone

From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:06:40 2006
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To: "Craig A. James" <cjames@modgraph-usa.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
References: <43CB71AC.20203@barettadeit.com> <9766.1137433907@sss.pgh.pa.us>
	<43CC0DDF.9080904@modgraph-usa.com>
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Craig A. James wrote:
> 
> Alessandro Baretta <a.baretta@barettadeit.com> writes:
>
> I think you're trying to do something at the wrong layer of your 
> architecture.  This task normally goes in your middleware layer, not 
> your database layer.

I am developing my applications in Objective Caml, and I have written the 
middleware layer myself. I could easily implement a cursor-pooling strategy, but 
there is no perfect solution to the problem of guaranteeing that cursors be 
closed. Remember that web applications require the user to "open a session" by 
connecting the appropriate HTTP resource, but users as never required to log 
out. Hence, in order to eventually reclaim all cursors, I must use magical 
"log-out detection" algorithm, which is usually implemented with a simple 
timeout. This guarantees the required property of safety (the population of 
cursors does not diverge) but does not guarantee the required property of 
liveness (a user connecting to the application, who has opened a session but has 
not logged out, and thus possesses a session token, should have access the 
execution context identified by his token).

Alex



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From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:19:39 2006
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To: Alessandro Baretta <a.baretta@barettadeit.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs 
In-reply-to: <43CD4BD0.9090807@barettadeit.com> 
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	<43CD4BD0.9090807@barettadeit.com>
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	message dated "Tue, 17 Jan 2006 20:56:00 +0100"
Date: Tue, 17 Jan 2006 15:19:31 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Alessandro Baretta <a.baretta@barettadeit.com> writes:
> * When the cursor state is pushed back to the backend, no new
> transaction is instantiated, but the XID of the original transaction
> is reused. In the MVCC system, this allows us to achieve a perfectly
> consistent view of the database at the instant the original
> transaction started, unless a VACUUM command has been executed in the
> meantime, in which case I would lose track of tuples which would have
> been live in the context of the original transaction, but have been
> updated or deleted and later vacuumed; however, this does not bother
> me at all.

> Is this not a viable solution?

No.  I'm not interested in "solutions" that can be translated as "you
may or may not get the right answer, and there's no way even to know
whether you did or not".  That might be acceptable for your particular
application but you certainly can't argue that it's of general
usefulness.

Also, I can't accept the concept of pushing the entire execution engine
state out to the client and then back again; that state is large enough
that doing so for every few dozen rows would yield incredibly bad
performance.  (In most scenarios I think it'd be just as efficient for
the client to pull the whole cursor output at the start and page through
it for itself.)  Worse yet: this would represent a security hole large
enough to wheel West Virginia through.  We'd have no reasonable way to
validate the data the client sends back.

Lastly, you underestimate the problems associated with not holding the
locks the cursor is using.  As an example, it's likely that a btree
indexscan wouldn't successfully restart at all, because it couldn't find
where it had been if the index page had been split or deleted meanwhile.
So not running VACUUM is not enough to guarantee the query will still
work.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:36:27 2006
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Subject: Re: big databases & hospitals
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References: <Pine.LNX.4.58.0601141307480.26994@zeus.gau.hu>
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On Sat, Jan 14, 2006 at 01:13:02PM +0100, Tomka Gergely wrote:
> Hi!
> 
> I need to write a few pages about Postgresql, to convince some suits. They
> have a few millions of records, on a few site, but they want to know the
> practical limits of Postgresql. So i need some information about the
> biggest (in storage space, in record number, in field number, and maybe
> table number) postgresql databases.
> 
> Additionally, because this company develops hospital information systems,
> if someone knows about a medical institute, which uses Postgresql, and
> happy, please send me infomation. I only now subscribed to the advocacy
> list, and only started to browse the archives.

We have a customer that has around 5000 tables and hasn't had any
serious issues from that number of tables (other than \d sometimes not
working in psql, but IIRC Tom put a fix in for that already).

As for raw size, 100G databases are pretty common. If you search through
the list archives you can probably find some examples.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:40:46 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Benjamin Arai <barai@cs.ucr.edu>, pgsql-performance@postgresql.org
Subject: Re: Ensuring data integrity with fsync=off
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On Sat, Jan 14, 2006 at 01:41:43PM -0500, Tom Lane wrote:
> "Benjamin Arai" <barai@cs.ucr.edu> writes:
> > Right now I run "sync" afte the updates have finished to ensure that the
> > data is synced to disk but I am concerned about the segment data and
> > anything else I am missing that PostgreSQL explicitly handles.  Is there
> > something I can do in addition to sync to tell PostgreSQL exlplicitly that
> > it is time to ensure everything is stored in its final destionation and etc?
> 
> You need to give PG a CHECKPOINT command to flush stuff out of its
> internal buffers.  After that finishes, a manual "sync" commnd will
> push everything down to disk.
> 
> You realize, of course, that a system failure while the updates are
> running might leave your database corrupt?  As long as you are prepared
> to restore from scratch, this might be a good tradeoff ... but don't
> let yourself get caught without an up-to-date backup ...

Another alternative that may (or may not) be simpler would be to run
everything in one transaction and just let that commit at the end. Also,
there is ongoing work towards allowing certain operations to occur
without generating any log writes. Currently there is code submitted
that allows COPY into a table that was created in the same transaction
to go un-logged, though I think it's only in HEAD. In any case, there
should be some features that could be very useful to you in 8.2.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 17 16:58:29 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Alessandro Baretta <a.baretta@barettadeit.com>
Cc: "Craig A. James" <cjames@modgraph-usa.com>,
	pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
Message-ID: <20060117205828.GE17896@pervasive.com>
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On Tue, Jan 17, 2006 at 09:06:53PM +0100, Alessandro Baretta wrote:
> Craig A. James wrote:
> >
> >Alessandro Baretta <a.baretta@barettadeit.com> writes:
> >
> >I think you're trying to do something at the wrong layer of your 
> >architecture.  This task normally goes in your middleware layer, not 
> >your database layer.
> 
> I am developing my applications in Objective Caml, and I have written the 
> middleware layer myself. I could easily implement a cursor-pooling 
> strategy, but there is no perfect solution to the problem of guaranteeing 
> that cursors be closed. Remember that web applications require the user to 
> "open a session" by connecting the appropriate HTTP resource, but users as 
> never required to log out. Hence, in order to eventually reclaim all 
> cursors, I must use magical "log-out detection" algorithm, which is usually 
> implemented with a simple timeout. This guarantees the required property of 
> safety (the population of cursors does not diverge) but does not guarantee 
> the required property of liveness (a user connecting to the application, 
> who has opened a session but has not logged out, and thus possesses a 
> session token, should have access the execution context identified by his 
> token).

With some "AJAX magic", it would probably be pretty easy to create an
application that let you know very quickly if a user left the
application (ie: browsed to another site, or closed the browser).
Essentially, you should be able to set it up so that it will ping the
application server fairly frequently (like every 10 seconds), so you
could drastically reduce the timeout interval.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 17 17:01:38 2006
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To: Yantao Shi <y.shi@larc.nasa.gov>
cc: pgsql-performance@postgresql.org
Subject: Re: wildcard search performance with "like" 
In-reply-to: <43CD4CE5.3020506@larcb.ecs.nasa.gov> 
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Comments: In-reply-to Yantao Shi <y.shi@larc.nasa.gov>
	message dated "Tue, 17 Jan 2006 15:00:37 -0500"
Date: Tue, 17 Jan 2006 16:01:33 -0500
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Yantao Shi <y.shi@larc.nasa.gov> writes:
> testdbspc=# explain select file_name from catalog where file_name like 
> 'MOD04_L2.A2005311.%.004.2005312013%.hdf';
> QUERY PLAN
> Seq Scan on catalog  (cost=0.00..429.00 rows=1 width=404)
>   Filter: (file_name ~~ 'MOD04_L2.A2005311.%.004.2005312013%.hdf'::text)
> (2 rows)

I'm betting you are using a non-C locale.  You need either to run the
database in C locale, or to create a special index type that is
compatible with LIKE searches.  See
http://www.postgresql.org/docs/8.1/static/indexes-opclass.html

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 17 17:04:06 2006
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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
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To: pgsql-performance@postgresql.org
Subject: Re: sum of left join greater than its parts
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Hmmm, this looks like a planner bug to me:

> Hash
> Join  (cost=870.00..992.56 rows=1 width=96) (actual time=90.566..125.782
> rows=472 loops=1) Hash Cond: (("outer".host_id = "inner".host_id) AND
> ("outer"."?column2?" = "inner".mtime)) ->  HashAggregate 
> (cost=475.88..495.32 rows=1555 width=16) (actual time=51.300..70.761
> rows=10870 loops=1)

>-- Nested Loop  (cost=1733.79..4620.38 rows=1 width=20) (actual
> time=81.160..89.826 rows=238 loops=1) ->  Nested Loop 
> (cost=1733.79..4615.92 rows=1 width=20) (actual time=81.142..86.826
> rows=238 loops=1) Join Filter: ("outer".rmsbinaryid =
> "inner".rmsbinaryid) ->  HashAggregate  (cost=1733.79..1740.92 rows=570
> width=12) (actual time=81.105..81.839 rows=323 loops=1) ->  Bitmap Heap
> Scan on msg306u  (cost=111.75..1540.65 rows=25752 width=12) (actual
> time=4.490..41.233 rows=25542 loops=1)

Notice that for both queries, the estimates are reasonably accurate (within 
+/- 4x) until they get to left joining the subquery, at which point the 
estimate of rows joined becomes exactly "1".   That looks suspicios to 
me ... Tom?  Neil?

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

From pgsql-performance-owner@postgresql.org  Tue Jan 17 17:13:56 2006
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From: mark@mark.mielke.cc
To: Alessandro Baretta <a.baretta@barettadeit.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
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On Tue, Jan 17, 2006 at 08:56:00PM +0100, Alessandro Baretta wrote:
> I understand most of these issues, and expected this kind of reply. Please, 
> allow me to insist that we reason on this problem and try to find a 
> solution. My reason for doing so is that the future software industry is 
> likely to see more and more web applications retrieving data from virtually 
> endless databases, and in such contexts, it is sensible to ask the final 
> client--the web client--to store the "cursor state", because web 
> interaction is intrinsically asynchronous, and you cannot count on users 
> logging out when they're done, releasing resources allocated to them. Think 
> of Google.

What is wrong with LIMIT and OFFSET? I assume your results are ordered
in some manner.

Especially with web users, who become bored if the page doesn't flicker
in a way that appeals to them, how could one have any expectation that
the cursor would ever be useful at all?

As a 'general' solution, I think optimizing the case where the same
query is executed multiple times, with only the LIMIT and OFFSET
parameters changing, would be a better bang for the buck. I'm thinking
along the lines of materialized views, for queries executed more than
a dozen times in a short length of time... :-)

In the mean time, I successfully use LIMIT and OFFSET without such an
optimization, and things have been fine for me.

Cheers,
mark

-- 
mark@mielke.cc / markm@ncf.ca / markm@nortel.com     __________________________
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From pgsql-performance-owner@postgresql.org  Tue Jan 17 17:40:52 2006
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Subject: Re: Suspending SELECTs
From: Mark Lewis <mark.lewis@mir3.com>
To: Alessandro Baretta <a.baretta@barettadeit.com>
Cc: pgsql-performance@postgresql.org
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> I am developing my applications in Objective Caml, and I have written the 
> middleware layer myself. I could easily implement a cursor-pooling strategy, but 
> there is no perfect solution to the problem of guaranteeing that cursors be 
> closed. Remember that web applications require the user to "open a session" by 
> connecting the appropriate HTTP resource, but users as never required to log 
> out. Hence, in order to eventually reclaim all cursors, I must use magical 
> "log-out detection" algorithm, which is usually implemented with a simple 
> timeout. This guarantees the required property of safety (the population of 
> cursors does not diverge) but does not guarantee the required property of 
> liveness (a user connecting to the application, who has opened a session but has 
> not logged out, and thus possesses a session token, should have access the 
> execution context identified by his token).

I fail to see the problem here.  Why should "liveness" be a required
property?  If is it simply that you can't promptly detect when a user is
finished with their web session so you can free resources, then remember
that there is no requirement that you dedicate a connection to their
session in the first place.  Even if you're using your own custom
middleware, it isn't a very complicated or conceptually difficult thing
to implement (see my previous post).  Certainly it's simpler than
allowing clients to pass around runtime state.

As far as implementing this sort of thing in the back-end, it would be
really hard with the PostgreSQL versioning model.  Oracle can more
easily (and kind of does) support cursors like you've described because
they implement MVCC differently than PostgreSQL, and in their
implementation you're guaranteed that you always have access to the most
recent x megabytes of historical rows, so even without an open
transaction to keep the required rows around you can still be relatively
sure they'll be around for "long enough".  In PostgreSQL, historical
rows are kept in the tables themselves and periodically vacuumed, so
there is no such guarantee, which means that you would need to either
implement a lot of complex locking for little material gain, or just
hold the cursors in moderately long-running transactions, which leads
back to the solution suggested earlier.

-- Mark Lewis



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From: J@Planeti.Biz
Message-ID: <05c301c61bb1$d88c6a00$681e140a@fatchubby>
To: <pgsql-performance@postgresql.org>
Subject: Multiple Order By Criteria
Date: Tue, 17 Jan 2006 17:03:27 -0500
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I'm trying to query a table with 250,000+ rows. My query requires I =
provide 5 colums in my "order by" clause:

select
   column
from table=20
where=20
 column >=3D '2004-3-22 0:0:0'
order by=20
    ds.receipt desc,
    ds.carrier_id asc,
    ds.batchnum asc,
    encounternum asc,
    ds.encounter_id ASC
limit 100 offset 0

I have an index built for each of these columns in my order by clause. =
This query takes an unacceptable amount of time to execute. Here are the =
results of the explain:

Limit  (cost=3D229610.78..229611.03 rows=3D100 width=3D717)
  ->  Sort  (cost=3D229610.78..230132.37 rows=3D208636 width=3D717)
        Sort Key: receipt, carrier_id, batchnum, encounternum, =
encounter_id
        ->  Seq Scan on detail_summary ds  (cost=3D0.00..22647.13 =
rows=3D208636 width=3D717)
              Filter: (receipt >=3D '2004-03-22'::date)


When I have the order by just have 1 criteria, it's fine (just =
ds.receipt DESC)

Limit  (cost=3D0.00..177.71 rows=3D100 width=3D717)
  ->  Index Scan Backward using detail_summary_receipt_id_idx on =
detail_summary ds  (cost=3D0.00..370756.84 rows=3D208636 width=3D717)
        Index Cond: (receipt >=3D '2004-03-22'::date)

I've increased my work_mem to up to 256meg with no speed increase. I =
think there's something here I just don't understand.

How do I make this go fast ?






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	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>I'm trying to query a table with =
250,000+ rows. My=20
query requires I provide 5 colums in my "order by" clause:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial =
size=3D2>select<BR>&nbsp;&nbsp;&nbsp;column</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>from&nbsp;table </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>where </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;column &gt;=3D '2004-3-22 =
0:0:0'<BR>order by=20
</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; ds.receipt =
desc,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; ds.carrier_id =
asc,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; ds.batchnum =
asc,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; encounternum =
asc,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; ds.encounter_id =
ASC</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>limit 100 offset 0</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>I have an index built for each of these =
columns in=20
my order by clause. This query takes an unacceptable amount of time to =
execute.=20
Here are the results of the explain:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Limit&nbsp; =
(cost=3D229610.78..229611.03 rows=3D100=20
width=3D717)<BR>&nbsp; -&gt;&nbsp; Sort&nbsp; =
(cost=3D229610.78..230132.37=20
rows=3D208636 width=3D717)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
Sort Key:=20
receipt, carrier_id, batchnum, encounternum,=20
encounter_id<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&gt;&nbsp; =
Seq Scan=20
on detail_summary ds&nbsp; (cost=3D0.00..22647.13 rows=3D208636=20
width=3D717)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;=20
Filter: (receipt &gt;=3D '2004-03-22'::date)<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>When I have the order by just have 1 =
criteria, it's=20
fine (just ds.receipt DESC)</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Limit&nbsp; (cost=3D0.00..177.71 =
rows=3D100=20
width=3D717)<BR>&nbsp; -&gt;&nbsp; Index Scan Backward using=20
detail_summary_receipt_id_idx on detail_summary ds&nbsp; =
(cost=3D0.00..370756.84=20
rows=3D208636 width=3D717)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
Index Cond:=20
(receipt &gt;=3D '2004-03-22'::date)</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>I've increased my work_mem to up to =
256meg with no=20
speed increase. I think there's something here I just don't=20
understand.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>How do I make this go fast ?</DIV>
<DIV><BR></DIV></FONT>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:19:55 2006
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From: Josh Berkus <josh@agliodbs.com>
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Organization: Aglio Database Solutions
To: pgsql-performance@postgresql.org
Subject: Re: Multiple Order By Criteria
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J,

> I have an index built for each of these columns in my order by clause.
> This query takes an unacceptable amount of time to execute. Here are the
> results of the explain:

You need a single index which has all five columns, in order.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:49:03 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Michael Riess <mlriess@gmx.de>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Tue, Jan 17, 2006 at 03:50:38PM +0100, Michael Riess wrote:
> Well,
> 
> I think that the documentation is not exactly easy to understand. I 
> always wondered why there are no examples for common postgresql 
> configurations. All I know is that the default configuration seems to be 
> too low for production use. And while running postgres I get no hints as 
> to which setting needs to be increased to improve performance. I have no 

There's a number of sites that have lots of info on postgresql.conf
tuning. Google for 'postgresql.conf tuning' or 'annotated
postgresql.conf'.

> chance to see if my FSM settings are too low other than to run vacuum 
> full verbose in psql, pipe the result to a text file and grep for some 
> words to get a somewhat comprehensive idea of how much unused space 
> there is in my system.
> 
> Don't get me wrong - I really like PostgreSQL and it works well in my 
> application. But somehow I feel that it might run much better ...
> 
> about the FSM: You say that increasing the FSM is fairly cheap - how 
> should I know that?

decibel@phonebook.1[16:26]/opt/local/share/postgresql8:3%grep fsm \
postgresql.conf.sample 
#max_fsm_pages = 20000                  # min max_fsm_relations*16, 6 bytes each
#max_fsm_relations = 1000               # min 100, ~70 bytes each
decibel@phonebook.1[16:26]/opt/local/share/postgresql8:4%
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:29:17 2006
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	<200601171425.38772.josh@agliodbs.com>
Subject: Re: Multiple Order By Criteria
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I created the index, in order. Did a vacuum analyze on the table and my 
explain still says:

Limit  (cost=229610.78..229611.03 rows=100 width=717)
  ->  Sort  (cost=229610.78..230132.37 rows=208636 width=717)
        Sort Key: receipt, carrier_id, batchnum, encounternum, encounter_id
        ->  Seq Scan on detail_summary ds  (cost=0.00..22647.13 rows=208636 
width=717)
              Filter: (receipt >= '2004-03-22'::date)


So, for fun I did
set enable_seqscan to off

But that didn't help. For some reason, the sort wants to do a seq scan and 
not use my super new index.

Am I doing something wrong ?

----- Original Message ----- 
From: "Josh Berkus" <josh@agliodbs.com>
To: <pgsql-performance@postgresql.org>
Cc: <J@planeti.biz>
Sent: Tuesday, January 17, 2006 5:25 PM
Subject: Re: [PERFORM] Multiple Order By Criteria


> J,
>
>> I have an index built for each of these columns in my order by clause.
>> This query takes an unacceptable amount of time to execute. Here are the
>> results of the explain:
>
> You need a single index which has all five columns, in order.
>

> -- 
> --Josh
>
> Josh Berkus
> Aglio Database Solutions
> San Francisco
>
> ---------------------------(end of broadcast)---------------------------
> TIP 1: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly
> 


From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:40:37 2006
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On Tue, 17 Jan 2006, Josh Berkus wrote:

> J,
>
> > I have an index built for each of these columns in my order by clause.
> > This query takes an unacceptable amount of time to execute. Here are the
> > results of the explain:
>
> You need a single index which has all five columns, in order.

I think he'll also need a reverse opclass for the first column in the
index or for the others since he's doing desc, asc, asc, asc, asc.

From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:50:45 2006
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On Tue, 17 Jan 2006 16:12:59 -0500
mark@mark.mielke.cc wrote:

> In the mean time, I successfully use LIMIT and OFFSET without such an
> optimization, and things have been fine for me.

  Same here. 

 ---------------------------------
   Frank Wiles <frank@wiles.org>
   http://www.wiles.org
 ---------------------------------


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From: Fredrick O Jackson <fred@arkansaswebs.com>
To: pgsql-performance@postgresql.org
Subject: Re: Multiple Order By Criteria
Date: Tue, 17 Jan 2006 16:57:06 -0600
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try adding the keyword 'date' before the date in your query.
I ran into this quite a while back, but I'm not sure I remember the solution.


 > In Reply to: Tuesday January 17 2006 04:29 pm, J@planeti.biz J@planeti.biz 
wrote:
> I created the index, in order. Did a vacuum analyze on the table and my
> explain still says:
>
> Limit  (cost=229610.78..229611.03 rows=100 width=717)
>   ->  Sort  (cost=229610.78..230132.37 rows=208636 width=717)
>         Sort Key: receipt, carrier_id, batchnum, encounternum, encounter_id
>         ->  Seq Scan on detail_summary ds  (cost=0.00..22647.13 rows=208636
> width=717)
>               Filter: (receipt >= '2004-03-22'::date)
>
>
> So, for fun I did
> set enable_seqscan to off
>
> But that didn't help. For some reason, the sort wants to do a seq scan and
> not use my super new index.
>
> Am I doing something wrong ?
>
> ----- Original Message -----
> From: "Josh Berkus" <josh@agliodbs.com>
> To: <pgsql-performance@postgresql.org>
> Cc: <J@planeti.biz>
> Sent: Tuesday, January 17, 2006 5:25 PM
> Subject: Re: [PERFORM] Multiple Order By Criteria
>
> > J,
> >
> >> I have an index built for each of these columns in my order by clause.
> >> This query takes an unacceptable amount of time to execute. Here are the
> >> results of the explain:
> >
> > You need a single index which has all five columns, in order.
> >
> >
> > --
> > --Josh
> >
> > Josh Berkus
> > Aglio Database Solutions
> > San Francisco
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 1: if posting/reading through Usenet, please send an appropriate
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> >       message can get through to the mailing list cleanly
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Have you searched our list archives?
>
>                http://archives.postgresql.org

From pgsql-performance-owner@postgresql.org  Tue Jan 17 18:53:15 2006
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Alessandro,

> I understand most of these issues, and expected this kind of reply.
> Please, allow me to insist that we reason on this problem and try to
> find a solution. My reason for doing so is that the future software
> industry is likely to see more and more web applications retrieving data
> from virtually endless databases, and in such contexts, it is sensible
> to ask the final client--the web client--to store the "cursor state",
> because web interaction is intrinsically asynchronous, and you cannot
> count on users logging out when they're done, releasing resources
> allocated to them. Think of Google.

I think you're trying to use an unreasonable difficult method to solve a 
problem that's already been solved multiple times.  What you want is 
called "query caching."   There are about 800 different ways to do this on 
the middleware or application layer which are 1000% easier than what 
you're proposing.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

From pgsql-performance-owner@postgresql.org  Tue Jan 17 19:03:20 2006
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From: J@Planeti.Biz
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Subject: Re: Multiple Order By Criteria
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I created the index like this:

CREATE INDEX rcbee_idx
  ON detail_summary
  USING btree
  (receipt, carrier_id, batchnum, encounternum, encounter_id);

Is this correct ?

How do I make a reverse opclass ?

----- Original Message ----- 
From: "Stephan Szabo" <sszabo@megazone.bigpanda.com>
To: "Josh Berkus" <josh@agliodbs.com>
Cc: <pgsql-performance@postgresql.org>; <J@planeti.biz>
Sent: Tuesday, January 17, 2006 5:40 PM
Subject: Re: [PERFORM] Multiple Order By Criteria


>
> On Tue, 17 Jan 2006, Josh Berkus wrote:
>
>> J,
>>
>> > I have an index built for each of these columns in my order by clause.
>> > This query takes an unacceptable amount of time to execute. Here are 
>> > the
>> > results of the explain:
>>
>> You need a single index which has all five columns, in order.
>
> I think he'll also need a reverse opclass for the first column in the
> index or for the others since he's doing desc, asc, asc, asc, asc.
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>       choose an index scan if your joining column's datatypes do not
>       match
> 


From pgsql-performance-owner@postgresql.org  Tue Jan 17 19:12:20 2006
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People:

To follow up further, what Alessandro is talking about is known as a 
"keyset cursor".   Sybase and SQL Server used to support them; I beleive 
that they were strictly read-only and had weird issues with record 
visibility.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

From pgsql-performance-owner@postgresql.org  Tue Jan 17 19:39:03 2006
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Subject: Re: Multiple Order By Criteria
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On Tue, 17 Jan 2006 J@Planeti.Biz wrote:

> I created the index like this:
>
> CREATE INDEX rcbee_idx
>   ON detail_summary
>   USING btree
>   (receipt, carrier_id, batchnum, encounternum, encounter_id);
>
> Is this correct ?

That would work if you were asking for all the columns ascending or
descending, but we don't currently use it for mixed orders.

> How do I make a reverse opclass ?

There's some information at the following:
http://archives.postgresql.org/pgsql-novice/2005-10/msg00254.php
http://archives.postgresql.org/pgsql-general/2005-01/msg00121.php
http://archives.postgresql.org/pgsql-general/2004-06/msg00565.php

From pgsql-performance-owner@postgresql.org  Tue Jan 17 20:23:34 2006
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I've read all of this info, closely. I wish when I was searching for an
answer for my problem these pages came up. Oh well.

I am getting an idea of what I need to do to make this work well. I was
wondering if there is more information to read on how to implement this
solution in a more simple way. Much of what's written seems to be towards an
audience that should understand certain things automatically.
----- Original Message ----- 
From: "Stephan Szabo" <sszabo@megazone.bigpanda.com>
To: <J@planeti.biz>
Cc: "Josh Berkus" <josh@agliodbs.com>; <pgsql-performance@postgresql.org>
Sent: Tuesday, January 17, 2006 6:39 PM
Subject: Re: [PERFORM] Multiple Order By Criteria


>
> On Tue, 17 Jan 2006 J@Planeti.Biz wrote:
>
>> I created the index like this:
>>
>> CREATE INDEX rcbee_idx
>>   ON detail_summary
>>   USING btree
>>   (receipt, carrier_id, batchnum, encounternum, encounter_id);
>>
>> Is this correct ?
>
> That would work if you were asking for all the columns ascending or
> descending, but we don't currently use it for mixed orders.
>
>> How do I make a reverse opclass ?
>
> There's some information at the following:
> http://archives.postgresql.org/pgsql-novice/2005-10/msg00254.php
> http://archives.postgresql.org/pgsql-general/2005-01/msg00121.php
> http://archives.postgresql.org/pgsql-general/2004-06/msg00565.php
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
> 


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Date: Wed, 18 Jan 2006 13:26:45 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Suspending SELECTs
In-reply-to: <20060117211259.GA13926@mark.mielke.cc>
To: mark@mark.mielke.cc
Cc: Alessandro Baretta <a.baretta@barettadeit.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
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mark@mark.mielke.cc wrote:
> On Tue, Jan 17, 2006 at 08:56:00PM +0100, Alessandro Baretta wrote:
> 
> 
> What is wrong with LIMIT and OFFSET? I assume your results are ordered
> in some manner.
> 
> Especially with web users, who become bored if the page doesn't flicker
> in a way that appeals to them, how could one have any expectation that
> the cursor would ever be useful at all?
> 
> As a 'general' solution, I think optimizing the case where the same
> query is executed multiple times, with only the LIMIT and OFFSET
> parameters changing, would be a better bang for the buck. I'm thinking
> along the lines of materialized views, for queries executed more than
> a dozen times in a short length of time... :-)
> 
> In the mean time, I successfully use LIMIT and OFFSET without such an
> optimization, and things have been fine for me.
> 

Second that.

I do seem to recall a case where I used a different variant of this 
method (possibly a database product that didn't have OFFSET, or maybe 
because OFFSET was expensive for the case in point), where the ORDER BY 
key for the last record on the page was saved and the query amended to 
use it filter for the "next' screen - e.g:

1st time in:

SELECT ... FROM table WHERE ... ORDER BY id LIMIT 20;

Suppose this displays records for id 10000 -> 10020.
When the user hits next, and page saves id=10020 in the session state 
and executes:

SELECT ... FROM table WHERE ... AND id > 10020 ORDER BY id LIMIT 20;

Clearly you have to be a little careful about whether to use '>' or '>=' 
depending on whether 'id' is unique or not (to continue using '>' in the 
non unique case, you can just save and use all the members of the 
primary key too).

Cheers

Mark

From pgsql-performance-owner@postgresql.org  Tue Jan 17 23:29:57 2006
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Date: Tue, 17 Jan 2006 19:29:44 -0800
From: Hari Warrier <hbhaskaran@gmail.com>
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Subject: Getting pg to use index on an inherited table (8.1.1)
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Hi,

I have two tables foobar and foobar2 (which inherits from foobar, no 
extra columns).
foobar2 has all the data (574,576 rows), foobar is empty.
Both foobar and foobar2 have an index on the only column 'id'.  Now I 
have a list of ids in a tmp_ids tables.
A query on foobar2 (child table) uses the index, whereas the same query 
via foobar (parent) doesn't.
Even if I set seq_scan off, it still doesn't use the index on the child 
table while queried via the parent table.

Details are given below. Any help is appreciated.

# analyze foobar;
ANALYZE
# analyze foobar2;
ANALYZE
# explain analyze select * from foobar2 join tmp_ids using (id);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=0.00..3013.69 rows=85856 width=4) (actual 
time=0.038..234.864 rows=44097 loops=1)
   ->  Seq Scan on tmp_ids  (cost=0.00..1.52 rows=52 width=4) (actual 
time=0.008..0.102 rows=52 loops=1)
   ->  Index Scan using foobar2_idx1 on foobar2  (cost=0.00..37.29 
rows=1651 width=4) (actual time=0.007..1.785 rows=848 loops=52)
         Index Cond: (foobar2.id = "outer".id)
 Total runtime: 302.963 ms
(5 rows)

# explain analyze select * from foobar join tmp_ids using (id);
                                                             QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=1.65..13267.85 rows=149946 width=4) (actual 
time=7.338..3837.060 rows=44097 loops=1)
   Hash Cond: ("outer".id = "inner".id)
   ->  Append  (cost=0.00..8883.16 rows=576716 width=4) (actual 
time=0.012..2797.555 rows=574576 loops=1)
         ->  Seq Scan on foobar  (cost=0.00..31.40 rows=2140 width=4) 
(actual time=0.002..0.002 rows=0 loops=1)
         ->  Seq Scan on foobar2 foobar  (cost=0.00..8851.76 rows=574576 
width=4) (actual time=0.004..1027.422 rows=574576 loops=1)
   ->  Hash  (cost=1.52..1.52 rows=52 width=4) (actual time=0.194..0.194 
rows=52 loops=1)
         ->  Seq Scan on tmp_ids  (cost=0.00..1.52 rows=52 width=4) 
(actual time=0.003..0.094 rows=52 loops=1)
 Total runtime: 3905.074 ms
(8 rows)

# select version();
                                          version
--------------------------------------------------------------------------------------------
 PostgreSQL 8.1.1 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 
3.3.3 (SuSE Linux)
(1 row)

# \d foobar
    Table "public.foobar"
 Column |  Type   | Modifiers
--------+---------+-----------
 id     | integer |
Indexes:
    "foobar_idx1" btree (id)

# \d foobar2
   Table "public.foobar2"
 Column |  Type   | Modifiers
--------+---------+-----------
 id     | integer |
Indexes:
    "foobar2_idx1" btree (id)
Inherits: foobar

# \d tmp_ids
   Table "public.tmp_ids"
 Column |  Type   | Modifiers
--------+---------+-----------
 id     | integer |


# set enable_seqscan=off;
SET
# explain analyze select * from foobar join tmp_ids using (id);
                                                                   QUERY 
PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=200000001.65..300013267.85 rows=149946 width=4) 
(actual time=7.352..3841.221 rows=44097 loops=1)
   Hash Cond: ("outer".id = "inner".id)
   ->  Append  (cost=100000000.00..200008883.16 rows=576716 width=4) 
(actual time=0.012..2803.547 rows=574576 loops=1)
         ->  Seq Scan on foobar  (cost=100000000.00..100000031.40 
rows=2140 width=4) (actual time=0.003..0.003 rows=0 loops=1)
         ->  Seq Scan on foobar2 foobar  
(cost=100000000.00..100008851.76 rows=574576 width=4) (actual 
time=0.005..1032.148 rows=574576 loops=1)
   ->  Hash  (cost=100000001.52..100000001.52 rows=52 width=4) (actual 
time=0.194..0.194 rows=52 loops=1)
         ->  Seq Scan on tmp_ids  (cost=100000000.00..100000001.52 
rows=52 width=4) (actual time=0.004..0.098 rows=52 loops=1)
 Total runtime: 3909.332 ms
(8 rows)

Output of  "show all" (remember I just turned off seq_scan above)

 enable_bitmapscan               | 
on                                        | Enables the planner's use of 
bitmap-scan plans.
 enable_hashagg                  | 
on                                        | Enables the planner's use of 
hashed aggregation plans.
 enable_hashjoin                 | 
on                                        | Enables the planner's use of 
hash join plans.
 enable_indexscan                | 
on                                        | Enables the planner's use of 
index-scan plans.
 enable_mergejoin                | 
on                                        | Enables the planner's use of 
merge join plans.
 enable_nestloop                 | 
on                                        | Enables the planner's use of 
nested-loop join plans.
 enable_seqscan                  | 
off                                       | Enables the planner's use of 
sequential-scan plans.
 enable_sort                     | 
on                                        | Enables the planner's use of 
explicit sort steps.
 enable_tidscan                  | 
on                                        | Enables the planner's use of 
TID scan plans.


From pgsql-performance-owner@postgresql.org  Tue Jan 17 23:48:15 2006
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Date: Tue, 17 Jan 2006 19:43:54 -0800
From: "Craig A. James" <cjames@modgraph-usa.com>
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CC: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
References: <43CB71AC.20203@barettadeit.com> <9766.1137433907@sss.pgh.pa.us>
	<43CC0DDF.9080904@modgraph-usa.com>
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Alessandro Baretta wrote:
>> I think you're trying to do something at the wrong layer of your 
>> architecture.  This task normally goes in your middleware layer, not 
>> your database layer.
> 
> I am developing my applications in Objective Caml, and I have written 
> the middleware layer myself. I could easily implement a cursor-pooling 
> strategy...

You're trying to solve a very hard problem, and you're rewriting a lot of stuff that's been worked on for years by teams of people.  If there's any way you switch use something like JBOSS, it might save you a lot of grief and hard work.

I eliminated this problem a different way, using what we call a "hitlist".  Basically, every query becomes a "select into", something like this:

  insert into hitlist_xxxx (select id from ...)

where "xxxx" is your user's id.  Once you do this, it's trivial to return each page to the user almost instantly using offset/limit, or by adding a "ROW_NUM" column of some sort.  We manage very large hitlists -- millions of rows.  Going from page 1 to page 100,000 takes a fraction of a second.

It also has the advantage that the user can come back in a week or a month and the results are still there.

The drawback are:

1. Before the user gets the first page, the entire query must complete.
2. You need a way to clean up old hitlists.
3. If you have tens of thousands of users, you'll have a large number of hitlists, and you have to use tablespaces to ensure that Linux filesystem directories don't get too large.
4. It takes space to store everyone's data.  (But disk space is so cheap this isn't much of an issue.)

You can eliminate #3 by a single shared hitlist with a column of UserID's.  But experience shows that a big shared hitlist doesn't work very well:  Inserts get slower because the UserID column must be indexed, and you can truncate individual hitlists but you have to delete from a shared hitlist.

Craig

From pgsql-performance-owner@postgresql.org  Wed Jan 18 00:02:30 2006
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To: Mark Kirkwood <markir@paradise.net.nz>
cc: mark@mark.mielke.cc, Alessandro Baretta <a.baretta@barettadeit.com>,
	pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs 
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	<43CD4BD0.9090807@barettadeit.com>
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	<43CD8B45.4090907@paradise.net.nz>
Comments: In-reply-to Mark Kirkwood <markir@paradise.net.nz>
	message dated "Wed, 18 Jan 2006 13:26:45 +1300"
Date: Tue, 17 Jan 2006 23:02:21 -0500
Message-ID: <4245.1137556941@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Mark Kirkwood <markir@paradise.net.nz> writes:
> SELECT ... FROM table WHERE ... ORDER BY id LIMIT 20;

> Suppose this displays records for id 10000 -> 10020.
> When the user hits next, and page saves id=10020 in the session state 
> and executes:

> SELECT ... FROM table WHERE ... AND id > 10020 ORDER BY id LIMIT 20;

> Clearly you have to be a little careful about whether to use '>' or '>=' 
> depending on whether 'id' is unique or not (to continue using '>' in the 
> non unique case, you can just save and use all the members of the 
> primary key too).

This is actually fairly painful to get right for a multi-column key
at the moment.  It'll be much easier once I finish up the
SQL-spec-row-comparison project.  See this thread for background:
http://archives.postgresql.org/pgsql-performance/2004-07/msg00188.php

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 18 00:07:10 2006
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To: Hari Warrier <hbhaskaran@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Getting pg to use index on an inherited table (8.1.1) 
In-reply-to: <43CDB628.3030007@gmail.com> 
References: <43CDB628.3030007@gmail.com>
Comments: In-reply-to Hari Warrier <hbhaskaran@gmail.com>
	message dated "Tue, 17 Jan 2006 19:29:44 -0800"
Date: Tue, 17 Jan 2006 23:07:05 -0500
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Hari Warrier <hbhaskaran@gmail.com> writes:
> A query on foobar2 (child table) uses the index, whereas the same query 
> via foobar (parent) doesn't.

A query just on foobar should be able to use the index AFAIR.  The
problem here is that you have a join, and we are not very good about
situations involving joins against inheritance sets (nor joins against
UNION ALL subqueries, which is really about the same thing).

I'm hoping to get a chance to look into improving this during the 8.2
development cycle.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 18 01:52:07 2006
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Date: Wed, 18 Jan 2006 18:51:58 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Suspending SELECTs
In-reply-to: <4245.1137556941@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: mark@mark.mielke.cc, Alessandro Baretta <a.baretta@barettadeit.com>,
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Tom Lane wrote:
> Mark Kirkwood <markir@paradise.net.nz> writes:
> 
>>SELECT ... FROM table WHERE ... ORDER BY id LIMIT 20;
> 
> 
>>Suppose this displays records for id 10000 -> 10020.
>>When the user hits next, and page saves id=10020 in the session state 
>>and executes:
> 
> 
>>SELECT ... FROM table WHERE ... AND id > 10020 ORDER BY id LIMIT 20;
> 
> 
>>Clearly you have to be a little careful about whether to use '>' or '>=' 
>>depending on whether 'id' is unique or not (to continue using '>' in the 
>>non unique case, you can just save and use all the members of the 
>>primary key too).
> 
> 
> This is actually fairly painful to get right for a multi-column key
> at the moment.  It'll be much easier once I finish up the
> SQL-spec-row-comparison project. 

Right, I think it was actually an Oracle 7.3 based web app (err... 
showing age here...) that I used this technique on.

Cheers

Mark

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Subject: Re: Multiple Order By Criteria
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-----Original Message-----
From: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org] On Behalf Of J@Planeti.Biz
Sent: Rabu, 18 Januari 2006 07:23
To: Stephan Szabo
Cc: Josh Berkus; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Multiple Order By Criteria

I've read all of this info, closely. I wish when I was searching for an
answer for my problem these pages came up. Oh well.
Well, I think you have to know about btree index. Btree is good enough,
although it's not better. It will perform best, if it doesn't index
too many multiple column.
In your case, you have to consentrate on 2 or 3 fields that will
use frequently. Put the most duplicate value on the front and others
are behind.
Eq: 
receipt, carrier_id, batchnum is the most frequently use, 
but the most duplicate value are: carrier_id, receipt, and batchnum
so make btree index (carrier_id, receipt, batchnum).
Btree will not suffer, and we also will advantage if the table
have relationship with other table with the same fields order. We have
not to make another index for that relation.

Best regards,
ahmad fajar.


> I am getting an idea of what I need to do to make this work well. I was
> wondering if there is more information to read on how to implement this
> solution in a more simple way. Much of what's written seems to be towards
> audience that should understand certain things automatically.
----- Original Message ----- 
From: "Stephan Szabo" <sszabo@megazone.bigpanda.com>
To: <J@planeti.biz>
Cc: "Josh Berkus" <josh@agliodbs.com>; <pgsql-performance@postgresql.org>
Sent: Tuesday, January 17, 2006 6:39 PM
Subject: Re: [PERFORM] Multiple Order By Criteria


>
> On Tue, 17 Jan 2006 J@Planeti.Biz wrote:
>
>> I created the index like this:
>>
>> CREATE INDEX rcbee_idx
>>   ON detail_summary
>>   USING btree
>>   (receipt, carrier_id, batchnum, encounternum, encounter_id);
>>
>> Is this correct ?
>
> That would work if you were asking for all the columns ascending or
> descending, but we don't currently use it for mixed orders.
>
>> How do I make a reverse opclass ?
>
> There's some information at the following:
> http://archives.postgresql.org/pgsql-novice/2005-10/msg00254.php
> http://archives.postgresql.org/pgsql-general/2005-01/msg00121.php
> http://archives.postgresql.org/pgsql-general/2004-06/msg00565.php
>


From pgsql-performance-owner@postgresql.org  Wed Jan 18 04:57:40 2006
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Subject: Re: Suspending SELECTs
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mark@mark.mielke.cc wrote:
> On Tue, Jan 17, 2006 at 08:56:00PM +0100, Alessandro Baretta wrote:
> 
>>I understand most of these issues, and expected this kind of reply. Please, 
>>allow me to insist that we reason on this problem and try to find a 
>>solution. My reason for doing so is that the future software industry is 
>>likely to see more and more web applications retrieving data from virtually 
>>endless databases, and in such contexts, it is sensible to ask the final 
>>client--the web client--to store the "cursor state", because web 
>>interaction is intrinsically asynchronous, and you cannot count on users 
>>logging out when they're done, releasing resources allocated to them. Think 
>>of Google.
> 
> 
> What is wrong with LIMIT and OFFSET? I assume your results are ordered
> in some manner.

It looks like this is the only possible solution at present--and in the future, 
too--but it has a tremendouse performance impact on queries returning thousands 
of rows.

Alex

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From pgsql-performance-owner@postgresql.org  Wed Jan 18 05:08:35 2006
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Alessandro Baretta schrieb:
> mark@mark.mielke.cc wrote:
> 
...
> 
> It looks like this is the only possible solution at present--and in the 
> future, too--but it has a tremendouse performance impact on queries 
> returning thousands of rows.
> 
Well actually one of the better solutions would be persistent cursors
(and therefore connection pooling). I bet this is easier then
fiddling with the problems of offset/limit and inventing even more
compex caching in the application.

Just my 0.02c
++Tino

From pgsql-performance-owner@postgresql.org  Wed Jan 18 07:15:32 2006
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Subject: Simple Question of Performance ILIKE or Lower
From: Marcos <mjs_ops@gmx.net>
To: pgsql-performance@postgresql.org
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Hi,

I have a simple question about performance using two resources.

What's have the best performance?

lower( col1 ) LIKE lower( 'myquestion%' )

OR

col1 ILIKE 'myquestion%'

Thanks.



From pgsql-performance-owner@postgresql.org  Wed Jan 18 05:14:38 2006
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Date: Wed, 18 Jan 2006 10:14:49 +0100
From: Alessandro Baretta <a.baretta@barettadeit.com>
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Subject: Re: Suspending SELECTs
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Josh Berkus wrote:
> People:
> 
> To follow up further, what Alessandro is talking about is known as a 
> "keyset cursor".   Sybase and SQL Server used to support them; I beleive 
> that they were strictly read-only and had weird issues with record 
> visibility.

I would like to thank everyone for sharing their ideas with me. I democratically 
accept the idea that my middleware will have to support the functionality I 
would have liked to delegate to PostgreSQL. If I have to implement anything of 
this sort--just like Tom--I don't want to spend time on a solution lacking 
generality or imposing unacceptable resource requirements under high load. The 
keyset-cursor idea is probably the best bet--and BTW, let me specifically thank 
Josh for mentioning them.

What I could do relatively easily is instantiate a thread to iteratively scan a 
traditional cursor N rows at a time, retrieving only record keys, and finally 
send them to the query-cache-manager. The application thread would then scan 
through the cursor results by fetching the rows associated to a given "page" of 
keys. I would have to keep the full cursor keyset in the application server's 
session state, but, hopefully, this is not nearly as bad as storing the entire 
recordset.

Alex



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From pgsql-performance-owner@postgresql.org  Wed Jan 18 10:06:10 2006
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I have the answer I've been looking for and I'd like to share with all. 
After help from you guys, it appeared that the real issue was using an index 
for my order by X DESC clauses. For some reason that doesn't make good 
sense, postgres doesn't support this, when it kinda should automatically.

Take the following end of an SQL statement.

order by
    col1 DESC
    col2 ASC
    col3 ASC

The first thing I learned is that you need an index that contains all these 
columns in it, in this order. If one of them has DESC then you have to 
create a function / operator class for each data type, in this case let's 
assume it's an int4. So, first thing you do is create a function that you're 
going to use in your operator:

create function
    int4_revcmp(int4,int4)  // --> cal the function whatever you want
    returns int4
    as 'select $2 - $1'
language sql;

Then you make your operator class.
CREATE OPERATOR CLASS int4_revop
      FOR TYPE int4 USING btree AS
          OPERATOR        1       > ,
          OPERATOR        2       >= ,
          OPERATOR        3       = ,
          OPERATOR        4       <= ,
          OPERATOR        5       < ,
          FUNCTION        1       int4_revcmp(int4, int4); // --> must be 
the name of your function you created.

Then when you make your index

create index rev_idx on table
    using btree(
        col1 int4_revop,    // --> must be name of operator class you 
defined.
        col2,
        col3
);

What I don't understand is how to make this function / operator class work 
with a text datatype. I tried interchanging the int4 with char and text and 
postgres didn't like the (as 'select $2 - $1') in the function, which I can 
kinda understand. Since I'm slighlty above my head at this point, I don't 
really know how to do it. Does any smart people here know how ?


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> There's a number of sites that have lots of info on postgresql.conf
> tuning. Google for 'postgresql.conf tuning' or 'annotated
> postgresql.conf'.

I know some of these sites, but who should I know if the information on 
those pages is correct? The information on those pages should be 
published as part of the postgres documentation. Doesn't have to be too 
much, maybe like this page:

http://www.powerpostgresql.com/Downloads/annotated_conf_80.html

But it should be part of the documentation to show newbies that not only 
the information is correct, but also approved of and recommended by the 
postgres team.

From pgsql-performance-owner@postgresql.org  Wed Jan 18 10:31:20 2006
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From: mark@mark.mielke.cc
To: Alessandro Baretta <a.baretta@barettadeit.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
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On Wed, Jan 18, 2006 at 09:57:50AM +0100, Alessandro Baretta wrote:
> mark@mark.mielke.cc wrote:
> >On Tue, Jan 17, 2006 at 08:56:00PM +0100, Alessandro Baretta wrote:
> >>I understand most of these issues, and expected this kind of reply. 
> >>Please, allow me to insist that we reason on this problem and try to find 
> >>a solution. My reason for doing so is that the future software industry 
> >>is likely to see more and more web applications retrieving data from 
> >>virtually endless databases, and in such contexts, it is sensible to ask 
> >>the final client--the web client--to store the "cursor state", because 
> >>web interaction is intrinsically asynchronous, and you cannot count on 
> >>users logging out when they're done, releasing resources allocated to 
> >>them. Think of Google.
> >What is wrong with LIMIT and OFFSET? I assume your results are ordered
> >in some manner.
> It looks like this is the only possible solution at present--and in the 
> future, too--but it has a tremendouse performance impact on queries 
> returning thousands of rows.

In the case of one web user generating one query, I don't see how it would
have a tremendous performance impact on large queries.

You mentioned google. I don't know how you use google - but most of the
people I know, rarely ever search through the pages. Generally the answer
we want is on the first page. If the ratio of users who search through
multiple pages of results, and users who always stop on the first page,
is anything significant (better than 2:1?) LIMIT and OFFSET are the
desired approach. Why have complicated magic in an application, for a
subset of the users?

I there is to be a change to PostgreSQL to optimize for this case, I
suggest it involve the caching of query plans, executor plans, query
results (materialized views?), LIMIT and OFFSET. If we had all of
this, you would have exactly what you want, while benefitting many
more people than just you. No ugly 'persistent state cursors' or
'import/export cursor state' implementation. People would automatically
benefit, without changing their applications.

Cheers,
mark

-- 
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From pgsql-performance-owner@postgresql.org  Wed Jan 18 11:06:17 2006
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Subject: Re: wildcard search performance with "like"
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As far as I know the index is only used when you do a prefix search, for 
example

col like 'xyz%'

I think that if you are looking for expressions such as 'A%B', you could 
rephrase them like this:

col like 'A%' AND col like 'A%B'

So the database could use the index to narrow down the result and then 
do a sequential search for the second condition.

Mike


Yantao Shi schrieb:
> Hi,
> 
> I have a postges 8.1.1 table with over 29 million rows in it. The colunm 
> (file_name) that I need to search on has entries like the following:
> 
> MOD04_L2.A2005311.1400.004.2005312013848.hdf                                                        
> 
> MYD04_L2.A2005311.0700.004.2005312013437.hdf                    
> I have an index on this column. But an index search is performance only 
> when I give the full file_name for search:
> 
> testdbspc=# explain select file_name from catalog where file_name = 
> 'MOD04_L2.A2005311.1400.004.2005312013848.hdf';
> QUERY PLAN
> Index Scan using catalog_pk_idx on catalog  (cost=0.00..6.01 rows=1 
> width=404)
>  Index Cond: (file_name = 
> 'MOD04_L2.A2005311.1400.004.2005312013848.hdf'::bpchar)
> (2 rows)
> 
> What I really need to do most of the time is a multi-wildcard search on 
> this column, which is now doing a whole table scan without using the 
> index at all:
> 
> testdbspc=# explain select file_name from catalog where file_name like 
> 'MOD04_L2.A2005311.%.004.2005312013%.hdf';
> QUERY PLAN
> Seq Scan on catalog  (cost=0.00..429.00 rows=1 width=404)
>  Filter: (file_name ~~ 'MOD04_L2.A2005311.%.004.2005312013%.hdf'::text)
> (2 rows)
> 
> Obviously, the performance of the table scan on such a large table is 
> not acceptable.
> 
> I tried full-text indexing and searching. It did NOT work on this column 
> because all the letters and numbers are linked together with "." and 
> considered one big single word by to_tsvector.
> 
> Any solutions for this column to use an index search with multiple wild 
> cards?
> 
> Thanks a lot,
> Yantao Shi
> 
> 
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 3: Have you checked our extensive FAQ?
> 
>               http://www.postgresql.org/docs/faq
> 

From pgsql-performance-owner@postgresql.org  Wed Jan 18 11:10:28 2006
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From: Stephan Szabo <sszabo@megazone.bigpanda.com>
To: J@Planeti.Biz
Cc: pgsql-performance@postgresql.org
Subject: Re: Multiple Order By Criteria
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On Wed, 18 Jan 2006 J@Planeti.Biz wrote:

> I have the answer I've been looking for and I'd like to share with all.
> After help from you guys, it appeared that the real issue was using an index
> for my order by X DESC clauses. For some reason that doesn't make good
> sense, postgres doesn't support this, when it kinda should automatically.

Well, the problem is that we do order with the index simply by through
following index order.  Standard index order is going to give you a sorted
order only in some particular order and its inverse.  IIRC, there are ways
to use an index in all ascending order to do mixed orders, but I think
those may involve traversing parts of the index multiple times and hasn't
been implemented.

> The first thing I learned is that you need an index that contains all these
> columns in it, in this order. If one of them has DESC then you have to
> create a function / operator class for each data type, in this case let's
> assume it's an int4. So, first thing you do is create a function that you're
> going to use in your operator:
>
> create function
>     int4_revcmp(int4,int4)  // --> cal the function whatever you want
>     returns int4
>     as 'select $2 - $1'
> language sql;
>
> Then you make your operator class.
> CREATE OPERATOR CLASS int4_revop
>       FOR TYPE int4 USING btree AS
>           OPERATOR        1       > ,
>           OPERATOR        2       >= ,
>           OPERATOR        3       = ,
>           OPERATOR        4       <= ,
>           OPERATOR        5       < ,
>           FUNCTION        1       int4_revcmp(int4, int4); // --> must be
> the name of your function you created.
>
> Then when you make your index
>
> create index rev_idx on table
>     using btree(
>         col1 int4_revop,    // --> must be name of operator class you
> defined.
>         col2,
>         col3
> );
>
> What I don't understand is how to make this function / operator class work
> with a text datatype. I tried interchanging the int4 with char and text and
> postgres didn't like the (as 'select $2 - $1') in the function, which I can
> kinda understand. Since I'm slighlty above my head at this point, I don't
> really know how to do it. Does any smart people here know how ?

I think having the function call the helper function for the normal
operator class for the type function with the arguments in reverse order
may work (or negating its output).

If you have any interest, there's an outstanding call for C versions of
the helper functions that we could then package up in contrib with the
operator class definitions.

From pgsql-performance-owner@postgresql.org  Wed Jan 18 11:11:54 2006
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mark@mark.mielke.cc wrote:
> On Wed, Jan 18, 2006 at 09:57:50AM +0100, Alessandro Baretta wrote:
> 
> I there is to be a change to PostgreSQL to optimize for this case, I
> suggest it involve the caching of query plans, executor plans, query
> results (materialized views?), LIMIT and OFFSET. If we had all of
> this, you would have exactly what you want, while benefitting many
> more people than just you. No ugly 'persistent state cursors' or
> 'import/export cursor state' implementation. People would automatically
> benefit, without changing their applications.

Actually, many of the features you mention (caching executor plans--that is 
imposing the use of prepared queries, caching query results and materializing 
views) I have already implemented in my "middleware". Somehow, apparently, my 
intuition on the problem of determining what ought to be delegated to the DBMS 
and what to the "middleware" is the opposites of most people on this list. As I 
mentioned earlier, I democratically accept the position of the majority--and 
monarchically I accept Tom's. And, scientifically, I have taken resposibility 
for proving myself wrong: I have stated my assumptions, I have formulated the 
hypothesis, I have designed an experiment capable of disproving it, and I have 
collected the data. Here are the steps and the results of the experiment.

Assumptions: Google defines the "best current practices" in web applications.

Hypothesis: The "best practice" for returning large data sets is to devise an 
algorithm (say, persistent cursors, for example) allowing subdivision of 
recordset is pages of a fixed maximum size, in such a way that sequentially 
fetching pages of records requires the system to compute each record only once.

Experiment: Given the stated assumption, record the time taken by Google to 
retrieve a sequence of pages of results, relative to the same query string. 
Repeat the experiment with different settings. Notice that Google actually 
displays on the results page the time taken to process the request.

Results: I'll omit the numerical data, which everyone can easily obtain in only 
a few minutes, repeating the experiment. I used several query strings containing 
very common words ("linux debian", "linux kernel", "linux tux"), each yielding 
millions of results. I set Google to retrieve 100 results per page. Then I ran 
the query and paged through the data set. The obvious result is that execution 
time is a monotonously growing function of the page number. This clearly 
indicates that Google does not use any algorithm of the proposed kind, but 
rather an OFFSET/LIMIT strategy, thus disproving the hypothesis.

It must also be noted that Google refuses to return more than 1000 results per 
query, thus indicating that the strategy the adopted quite apparently cannot 
scale indefinitely, for on a query returning a potentially flooding dataset, a 
user paging through the data would experience a linear slowdown on the number of 
pages already fetched, and the DBMS workload would also be linear on the number 
of fetched pages.

I do not like this approach, but the fact that Google came up with no better 
solution is a clear indication that Tome et al. are more than correct.

Alex

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From pgsql-performance-owner@postgresql.org  Wed Jan 18 11:50:51 2006
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Message-ID: <034701c61c46$f427df20$f20214ac@bite.lt>
From: "Mindaugas" <mind@bi.lt>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: <pgsql-performance@postgresql.org>
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Subject: Re: Autovacuum / full vacuum 
Date: Wed, 18 Jan 2006 17:50:49 +0200
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> >> Even a database-wide vacuum does not take locks on more than one table.
> >> The table locks are acquired and released one by one, as the operation
> >> proceeds.
> 
> > Has that changed recently?  I have always seen "vacuumdb" or SQL
> > "VACUUM" (without table specifications) running as one long
> > transaction which doesn't release the locks that it is granted until
> > the end of the transaction.
> 
> You sure?  It's not supposed to, and watching a database-wide vacuum
> with "select * from pg_locks" doesn't look to me like it ever has locks
> on more than one table (plus the table's indexes and toast table).

  Are there some plans to remove vacuum altogether?

  Mindaugas


From pgsql-performance-owner@postgresql.org  Wed Jan 18 12:51:18 2006
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From: mark@mark.mielke.cc
To: Harry Jackson <harryjackson@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Suspending SELECTs
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On Wed, Jan 18, 2006 at 03:41:57PM +0000, Harry Jackson wrote:
> There are various reason why google might  want to limit the search
> result returned ie to encourage people to narrow their search. Prevent
> screen scrapers from hitting them really hard blah blah. Perhaps less
> than 0.00000001% of real users (not scrapers) actually dig down to the
> 10th page so whats the point.

I recall a day when google crashed, apparently due to a Windows virus
that would use google to obtain email addresses.

As an unsubstantiated theory - this may have involved many, many clients,
all accessing search page results beyond the first page.

I don't see google optimizing for the multiple page scenario. Most
people (as I think you agree above), are happy with the first or
second page, and they are gone. Keeping a cursor for these people as
anything more than an offset into search criteria, would not be
useful.

Cheers,

-- 
mark@mielke.cc / markm@ncf.ca / markm@nortel.com     __________________________
.  .  _  ._  . .   .__    .  . ._. .__ .   . . .__  | Neighbourhood Coder
|\/| |_| |_| |/    |_     |\/|  |  |_  |   |/  |_   | 
|  | | | | \ | \   |__ .  |  | .|. |__ |__ | \ |__  | Ottawa, Ontario, Canada

  One ring to rule them all, one ring to find them, one ring to bring them all
                       and in the darkness bind them...

                           http://mark.mielke.cc/


From pgsql-performance-owner@postgresql.org  Wed Jan 18 13:04:13 2006
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Subject: Re: Autovacuum / full vacuum
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mind@bi.lt ("Mindaugas") writes:
>> >> Even a database-wide vacuum does not take locks on more than one
>> >> table.  The table locks are acquired and released one by one, as
>> >> the operation proceeds.
>> 
>> > Has that changed recently?  I have always seen "vacuumdb" or SQL
>> > "VACUUM" (without table specifications) running as one long
>> > transaction which doesn't release the locks that it is granted
>> > until the end of the transaction.
>> 
>> You sure?  It's not supposed to, and watching a database-wide
>> vacuum with "select * from pg_locks" doesn't look to me like it
>> ever has locks on more than one table (plus the table's indexes and
>> toast table).
>
>   Are there some plans to remove vacuum altogether?

I don't see that on the TODO list...

http://www.postgresql.org/docs/faqs.TODO.html

To the contrary, there is a whole section on what functionality to
*ADD* to VACUUM.
-- 
let name="cbbrowne" and tld="acm.org" in String.concat "@" [name;tld];;
http://www.ntlug.org/~cbbrowne/finances.html
"There are two types of hackers working on Linux: those who can spell,
and those who can't.  There  is a constant, pitched battle between the
two  camps."  
--Russ Nelson (Linux Kernel Summary, Ver. 1.1.75 -> 1.1.76)

From pgsql-performance-owner@postgresql.org  Wed Jan 18 12:53:04 2006
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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Mindaugas <mind@bi.lt>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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Mindaugas wrote:
> > >> Even a database-wide vacuum does not take locks on more than one table.
> > >> The table locks are acquired and released one by one, as the operation
> > >> proceeds.
> > 
> > > Has that changed recently?  I have always seen "vacuumdb" or SQL
> > > "VACUUM" (without table specifications) running as one long
> > > transaction which doesn't release the locks that it is granted until
> > > the end of the transaction.
> > 
> > You sure?  It's not supposed to, and watching a database-wide vacuum
> > with "select * from pg_locks" doesn't look to me like it ever has locks
> > on more than one table (plus the table's indexes and toast table).
> 
>   Are there some plans to remove vacuum altogether?

No, but there are plans to make it as automatic and unintrusive as
possible.  (User configuration will probably always be needed.)

-- 
Alvaro Herrera                           Developer, http://www.PostgreSQL.org
FOO MANE PADME HUM

From pgsql-performance-owner@postgresql.org  Wed Jan 18 14:10:00 2006
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From: "Benjamin Arai" <barai@cs.ucr.edu>
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Hi,
 
I am currently doing large weekly updates with fsync=off.  My updates
involves SELECT, UPDATE, DELETE and etc.  Setting fsync=off works for me
since I take a complete backup before the weekly update and run a "sync" and
"CHECKPOINT" after each weekly update has completed to ensure the data is
all written to disk.  
 
Obviously, I have done this to improve write performance for the update each
week.  My question is if I install a 3ware or similar card to replace my
current software RAID 1 configuration, am I going to see a very large
improvement?  If so, what would be a ball park figure?
 
Benjamin Arai
barai@cs.ucr.edu
http://www.benjaminarai.com <http://www.benjaminarai.com/> 
 

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<BODY>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
size=3D2>Hi,</FONT></SPAN></DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial size=3D2>I am =
currently doing=20
large weekly updates with fsync=3Doff.&nbsp; My updates involves SELECT, =
UPDATE,=20
DELETE and etc.&nbsp; Setting fsync=3Doff works for me since I take a =
complete=20
backup before the weekly update and run a "sync" and "CHECKPOINT" after =
each=20
weekly update has completed to ensure the data is all written to =
disk.&nbsp;=20
</FONT></SPAN></DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial =
size=3D2>Obviously, I have=20
done this to improve write performance for the&nbsp;update each =
week.&nbsp; My=20
question is if&nbsp;I install a 3ware or similar card to replace my =
current=20
software RAID 1 configuration, am I going to see a very large =
improvement?&nbsp;=20
If so, what would be a ball park figure?</FONT></SPAN></DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D661250518-18012006><FONT face=3DArial size=3D2>
<DIV align=3Dleft><FONT face=3DArial><STRONG>Benjamin =
Arai</STRONG></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"mailto:barai@cs.ucr.edu">barai@cs.ucr.edu</A></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"http://www.benjaminarai.com/">http://www.benjaminarai.com</A></FO=
NT></DIV>
<DIV align=3Dleft><FONT face=3DArial=20
size=3D2></FONT>&nbsp;</DIV></FONT></SPAN></DIV></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Wed Jan 18 14:21:31 2006
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From: "Joshua D. Drake" <jd@commandprompt.com>
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To: Benjamin Arai <barai@cs.ucr.edu>
CC: pgsql-performance@postgresql.org
Subject: Re: 3WARE Card performance boost?
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> Obviously, I have done this to improve write performance for the update 
> each week.  My question is if I install a 3ware or similar card to 
> replace my current software RAID 1 configuration, am I going to see a 
> very large improvement?  If so, what would be a ball park figure?

Well that entirely depends on what level...

1. I would suggest LSI 150-6 not 3ware

   Why?

Because 3ware does not make a midrange card that has a battery backed 
cache :). That is the only reason. 3ware makes good stuff.

So anyway... LSI150-6 with Battery Backed cache option. Put 6 drives
on it with a RAID 10 array, turn on write cache and you should have
a hauling drive.

Joshua D. Drake



>  
> *Benjamin Arai*
> barai@cs.ucr.edu <mailto:barai@cs.ucr.edu>
> http://www.benjaminarai.com <http://www.benjaminarai.com/>
>  


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From pgsql-performance-owner@postgresql.org  Wed Jan 18 14:26:45 2006
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From: "Benjamin Arai" <barai@cs.ucr.edu>
To: <pgsql-performance@postgresql.org>
Subject: Re: 3WARE Card performance boost?
Date: Wed, 18 Jan 2006 10:26:37 -0800
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My original plan was to buy a 3WARE card and put a 1GB of memory on it to
improve writes but I am not sure if that is actually going to help the issue
if fsync=off.
 
Benjamin Arai
barai@cs.ucr.edu
http://www.benjaminarai.com <http://www.benjaminarai.com/> 
 


  _____  

From: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org] On Behalf Of Benjamin Arai
Sent: Wednesday, January 18, 2006 10:10 AM
To: pgsql-performance@postgresql.org
Subject: [PERFORM] 3WARE Card performance boost?


Hi,
 
I am currently doing large weekly updates with fsync=off.  My updates
involves SELECT, UPDATE, DELETE and etc.  Setting fsync=off works for me
since I take a complete backup before the weekly update and run a "sync" and
"CHECKPOINT" after each weekly update has completed to ensure the data is
all written to disk.  
 
Obviously, I have done this to improve write performance for the update each
week.  My question is if I install a 3ware or similar card to replace my
current software RAID 1 configuration, am I going to see a very large
improvement?  If so, what would be a ball park figure?
 

Benjamin Arai
barai@cs.ucr.edu
http://www.benjaminarai.com <http://www.benjaminarai.com/> 
 


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<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Dus-ascii">
<META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR></HEAD>
<BODY>
<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff size=3D2>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D708192518-18012006><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>My original plan was to buy a 3WARE card and =
put a 1GB of=20
memory on it to improve writes but I am not sure if that is actually =
going to=20
help the issue if fsync=3Doff.</FONT></SPAN></DIV>
<DIV>&nbsp;</DIV>
<DIV align=3Dleft><FONT face=3DArial><STRONG>
<DIV align=3Dleft><FONT face=3DArial><STRONG>Benjamin =
Arai</STRONG></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"mailto:barai@cs.ucr.edu">barai@cs.ucr.edu</A></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"http://www.benjaminarai.com/">http://www.benjaminarai.com</A></FO=
NT></DIV>
<DIV align=3Dleft><FONT face=3DArial=20
size=3D2></FONT>&nbsp;</DIV></STRONG></FONT></FONT></DIV></DIV><BR>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid; MARGIN-RIGHT: 0px">
  <DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
  <HR tabIndex=3D-1>
  <FONT face=3DTahoma size=3D2><B>From:</B> =
pgsql-performance-owner@postgresql.org=20
  [mailto:pgsql-performance-owner@postgresql.org] <B>On Behalf Of =
</B>Benjamin=20
  Arai<BR><B>Sent:</B> Wednesday, January 18, 2006 10:10 =
AM<BR><B>To:</B>=20
  pgsql-performance@postgresql.org<BR><B>Subject:</B> [PERFORM] 3WARE =
Card=20
  performance boost?<BR></FONT><BR></DIV>
  <DIV></DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
  size=3D2>Hi,</FONT></SPAN></DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
  size=3D2></FONT></SPAN>&nbsp;</DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial size=3D2>I am =
currently=20
  doing large weekly updates with fsync=3Doff.&nbsp; My updates involves =
SELECT,=20
  UPDATE, DELETE and etc.&nbsp; Setting fsync=3Doff works for me since I =
take a=20
  complete backup before the weekly update and run a "sync" and =
"CHECKPOINT"=20
  after each weekly update has completed to ensure the data is all =
written to=20
  disk.&nbsp; </FONT></SPAN></DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
  size=3D2></FONT></SPAN>&nbsp;</DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial =
size=3D2>Obviously, I have=20
  done this to improve write performance for the&nbsp;update each =
week.&nbsp; My=20
  question is if&nbsp;I install a 3ware or similar card to replace my =
current=20
  software RAID 1 configuration, am I going to see a very large=20
  improvement?&nbsp; If so, what would be a ball park=20
figure?</FONT></SPAN></DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial=20
  size=3D2></FONT></SPAN>&nbsp;</DIV>
  <DIV><SPAN class=3D661250518-18012006><FONT face=3DArial size=3D2>
  <DIV align=3Dleft><FONT face=3DArial><STRONG>Benjamin =
Arai</STRONG></FONT></DIV>
  <DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
  href=3D"mailto:barai@cs.ucr.edu">barai@cs.ucr.edu</A></FONT></DIV>
  <DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
  =
href=3D"http://www.benjaminarai.com/">http://www.benjaminarai.com</A></FO=
NT></DIV>
  <DIV align=3Dleft><FONT face=3DArial=20
size=3D2></FONT>&nbsp;</DIV></FONT></SPAN></DIV></BLOCKQUOTE></BODY></HTM=
L>

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From pgsql-performance-owner@postgresql.org  Wed Jan 18 14:54:22 2006
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Date: Wed, 18 Jan 2006 13:54:16 -0500
From: Michael Adler <adler@pobox.com>
To: Charles Sprickman <spork@bway.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: SAN/NAS options
Message-ID: <20060118185415.GF24298@pobox.com>
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On Sat, Jan 14, 2006 at 09:37:01PM -0500, Charles Sprickman wrote:
> Following up to myself again...
> 
> On Wed, 14 Dec 2005, Charles Sprickman wrote:
> 
> >Hello all,
> >
> >Supermicro 1U w/SCA backplane and 4 bays
> >2x2.8 GHz Xeons
> >Adaptec 2015S "zero channel" RAID card
> 
> I don't want to throw away the four machines like that that we have.  I do 
> want to throw away the ZCR cards... :)  If I ditch those I still have a 1U 
> box with a U320 scsi plug on the back.
> 
> I'm vaguely considering pairing these two devices:
> 
> http://www.areca.us/products/html/products.htm
> 
> That's an Areca 16 channel SATA II (I haven't even read up on what's new 
> in SATA II) RAID controller with an optional U320 SCSI daughter card to 
> connect to the host(s).
> 
> http://www.chenbro.com.tw/Chenbro_Special/RM321.php

Not sure how significant, but the RM321 backplane claims to support
SATA 150 (aka SATA I) only.

 -Mike

From pgsql-performance-owner@postgresql.org  Wed Jan 18 15:12:49 2006
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Date: Wed, 18 Jan 2006 14:12:43 -0500
From: Alex Turner <armtuk@gmail.com>
To: "Joshua D. Drake" <jd@commandprompt.com>
Subject: Re: 3WARE Card performance boost?
Cc: Benjamin Arai <barai@cs.ucr.edu>, pgsql-performance@postgresql.org
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http://www.3ware.com/products/serial_ata2-9000.asp

Check their data sheet - the cards are BBU ready - all you have to do
is order a BBU
which you can from here:
http://www.newegg.com/Product/Product.asp?Item=3DN82E16815999601


Alex.

On 1/18/06, Joshua D. Drake <jd@commandprompt.com> wrote:
>
> > Obviously, I have done this to improve write performance for the update
> > each week.  My question is if I install a 3ware or similar card to
> > replace my current software RAID 1 configuration, am I going to see a
> > very large improvement?  If so, what would be a ball park figure?
>
> Well that entirely depends on what level...
>
> 1. I would suggest LSI 150-6 not 3ware
>
>    Why?
>
> Because 3ware does not make a midrange card that has a battery backed
> cache :). That is the only reason. 3ware makes good stuff.
>
> So anyway... LSI150-6 with Battery Backed cache option. Put 6 drives
> on it with a RAID 10 array, turn on write cache and you should have
> a hauling drive.
>
> Joshua D. Drake
>
>
>
> >
> > *Benjamin Arai*
> > barai@cs.ucr.edu <mailto:barai@cs.ucr.edu>
> > http://www.benjaminarai.com <http://www.benjaminarai.com/>
> >
>
>
> --
> The PostgreSQL Company - Command Prompt, Inc. 1.503.667.4564
> PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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From pgsql-performance-owner@postgresql.org  Wed Jan 18 15:15:56 2006
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From: Michael Crozier <crozierm@conducivetech.com>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
Date: Wed, 18 Jan 2006 11:15:51 -0800
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On Wednesday 18 January 2006 08:54 am, Chris Browne wrote:
> To the contrary, there is a whole section on what functionality to
> *ADD* to VACUUM.

Near but not quite off the topic of VACUUM and new features...

I've been thinking about parsing the vacuum output and storing it in 
Postgresql.  All the tuple, page, cpu time, etc... information would be 
inserted into a reasonably flat set of tables.

The benefits I would expect from this are:

* monitoring ability - I could routinely monitor the values in the table to 
warn when vacuum's are failing or reclaimed space has risen dramatically.  I 
find it easier to write and maintain monitoring agents that perform SQL 
queries than ones that need to routinely parse log files and coordinate with 
cron.

* historical perspective on tuple use - which a relatively small amount of 
storage, I could use the vacuum output to get an idea of usage levels over 
time, which is beneficial for planning additional capacity

* historical information could theoretically inform the autovacuum, though I 
assume there are better alternatives planned.

* it could cut down on traffic on this list if admin could see routine 
maintenance in a historical context.

Assuming this isn't a fundamentally horrible idea, it would be nice if there 
were ways to do this without parsing the pretty-printed vacuum text (ie, 
callbacks, triggers, guc variable).

I'd like to know if anybody does this already, thinks its a bad idea, or can 
knock me on the noggin with the pg manual and say, "it's already there!".

Regards,

 Michael


From pgsql-performance-owner@postgresql.org  Wed Jan 18 15:17:10 2006
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Date: Wed, 18 Jan 2006 14:17:04 -0500
From: Alex Turner <armtuk@gmail.com>
To: Benjamin Arai <barai@cs.ucr.edu>
Subject: Re: 3WARE Card performance boost?
Cc: pgsql-performance@postgresql.org
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A 3ware card will re-order your writes to put them more in disk order,
which will probably improve performance a bit, but just going from a
software RAID 1 to a hardware RAID 1, I would not imagine that you
will see much of a performance boost.  Really to get better
performance you will need to add more drives, or faster drives.  If
you are currently running 7200 RPM consumer drives, going to a
10000RPM WD Raptor drive will probably increase performance by about
30%, again not all that much.

Alex

On 1/18/06, Benjamin Arai <barai@cs.ucr.edu> wrote:
>
> Hi,
>
> I am currently doing large weekly updates with fsync=3Doff.  My updates
> involves SELECT, UPDATE, DELETE and etc.  Setting fsync=3Doff works for m=
e
> since I take a complete backup before the weekly update and run a "sync" =
and
> "CHECKPOINT" after each weekly update has completed to ensure the data is
> all written to disk.
>
> Obviously, I have done this to improve write performance for the update e=
ach
> week.  My question is if I install a 3ware or similar card to replace my
> current software RAID 1 configuration, am I going to see a very large
> improvement?  If so, what would be a ball park figure?
>
>
> Benjamin Arai
> barai@cs.ucr.edu
> http://www.benjaminarai.com
>

From pgsql-performance-owner@postgresql.org  Wed Jan 18 15:23:32 2006
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	18 Jan 2006 20:23:25 +0100
Subject: Re: 3WARE Card performance boost?
From: Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>
To: Benjamin Arai <barai@cs.ucr.edu>
Cc: pgsql-performance@postgresql.org
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On Wed, 2006-01-18 at 10:26 -0800, Benjamin Arai wrote:
> My original plan was to buy a 3WARE card and put a 1GB of memory on it
> to improve writes but I am not sure if that is actually going to help
> the issue if fsync=off.
My experience with a 3Ware 9500S-8 card are rather disappointing,
especially the write performance of the card, which is extremely poor.
Reading is OK.


-- 
Groeten,

Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J.Kraaijeveld@Askesis.nl
web: www.askesis.nl 



From pgsql-performance-owner@postgresql.org  Wed Jan 18 15:37:45 2006
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From: J@Planeti.Biz
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To: "Stephan Szabo" <sszabo@megazone.bigpanda.com>
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Subject: Re: Multiple Order By Criteria
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Here's some C to use to create the operator classes, seems to work ok.
---

#include "postgres.h"
#include <string.h>
#include "fmgr.h"
#include "utils/date.h"

/* For date sorts */

PG_FUNCTION_INFO_V1(ddd_date_revcmp);

Datum   ddd_date_revcmp(PG_FUNCTION_ARGS){
        DateADT         arg1=PG_GETARG_DATEADT(0);
        DateADT         arg2=PG_GETARG_DATEADT(1);

        PG_RETURN_INT32(arg2 - arg1);
}

/* For integer sorts */

PG_FUNCTION_INFO_V1(ddd_int_revcmp);

Datum   ddd_int_revcmp(PG_FUNCTION_ARGS){
        int32           arg1=PG_GETARG_INT32(0);
        int32           arg2=PG_GETARG_INT32(1);

        PG_RETURN_INT32(arg2 - arg1);
}

/* For string sorts */

PG_FUNCTION_INFO_V1(ddd_text_revcmp);

Datum   ddd_text_revcmp(PG_FUNCTION_ARGS){
        text*           arg1=PG_GETARG_TEXT_P(0);
        text*           arg2=PG_GETARG_TEXT_P(1);

        PG_RETURN_INT32(strcmp((char*)VARDATA(arg2),(char*)VARDATA(arg1)));
}


/*
create function ddd_date_revcmp(date,date) returns int4 as 
'/data/postgres/contrib/cmplib.so', 'ddd_date_revcmp' LANGUAGE C STRICT;
create function ddd_int_revcmp(int4,int4) returns int4 as 
'/data/postgres/contrib/cmplib.so', 'ddd_int_revcmp' LANGUAGE C STRICT;
create function ddd_text_revcmp(text,text) returns int4 as 
'/data/postgres/contrib/cmplib.so', 'ddd_text_revcmp' LANGUAGE C STRICT;
 */

----- Original Message ----- 
From: "Stephan Szabo" <sszabo@megazone.bigpanda.com>
To: <J@Planeti.Biz>
Sent: Wednesday, January 18, 2006 2:24 PM
Subject: Re: [PERFORM] Multiple Order By Criteria


> On Wed, 18 Jan 2006 J@Planeti.Biz wrote:
>
>> Could you explain to me how do create this operator class for a text data
>> type ? I think it will give me more of an understanding of what's going 
>> on
>> if I could see this example.
>
> Using an SQL function (mostly because I'm too lazy to look up the C call
> syntax) I think it'd be something like:
>
> create function bttextrevcmp(text, text) returns int4 as
> 'select bttextcmp($2, $1)' language 'sql';
>
> CREATE OPERATOR CLASS text_revop
>      FOR TYPE text USING btree AS
>          OPERATOR        1       > ,
>          OPERATOR        2       >= ,
>          OPERATOR        3       = ,
>          OPERATOR        4       <= ,
>          OPERATOR        5       < ,
>          FUNCTION        1       bttextrevcmp(text,text);
>
> I believe bttextcmp is the standard text btree operator class helper
> function, so we call it with reverse arguments to try to flip its results
> (I think -bttextcmp($1,$2) would also work).
> 


From pgsql-performance-owner@postgresql.org  Wed Jan 18 16:28:40 2006
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Date: Wed, 18 Jan 2006 13:28:25 -0700
From: Michael Fuhr <mike@fuhr.org>
To: Marcos <mjs_ops@gmx.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Use of Stored Procedures and
Message-ID: <20060118202825.GA94306@winnie.fuhr.org>
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On Tue, Jan 17, 2006 at 09:04:53AM +0000, Marcos wrote:
> I already read the documentation for to use the SPI_PREPARE and
> SPI_EXEC... but sincerely I don't understand how I will use this
> resource in my statements.

What statements?  What problem are you trying to solve?

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Wed Jan 18 17:58:19 2006
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Subject: Re: 3WARE Card performance boost?
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Benjamin Arai wrote:
> Obviously, I have done this to improve write performance for the update 
> each week.  My question is if I install a 3ware or similar card to 
> replace my current software RAID 1 configuration, am I going to see a 
> very large improvement?  If so, what would be a ball park figure?

The key is getting a card with the ability to upgrade the onboard ram.

Our previous setup was a LSI MegaRAID 320-1 (128MB), 4xRAID10, 
fsync=off. Replaced it with a ARC-1170 (1GB) w/ 24x7200RPM SATA2 drives 
(split into 3 8-drive RAID6 arrays) and performance for us is through 
the ceiling.

For OLTP type updates, we've gotten about +80% increase. For massive 
1-statement updates, performance increase is in the +triple digits.

From pgsql-performance-owner@postgresql.org  Wed Jan 18 18:02:30 2006
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Date: Wed, 18 Jan 2006 23:02:32 +0100
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: 3WARE Card performance boost?
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On Wed, Jan 18, 2006 at 01:58:09PM -0800, William Yu wrote:
> The key is getting a card with the ability to upgrade the onboard ram.
> 
> Our previous setup was a LSI MegaRAID 320-1 (128MB), 4xRAID10, 
> fsync=off. Replaced it with a ARC-1170 (1GB) w/ 24x7200RPM SATA2 drives 
> (split into 3 8-drive RAID6 arrays) and performance for us is through 
> the ceiling.

Well, the fact that you went from four to 24 disks would perhaps be a bigger
factor than the amount of RAM...

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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crozierm@conducivetech.com (Michael Crozier) writes:

> On Wednesday 18 January 2006 08:54 am, Chris Browne wrote:
>> To the contrary, there is a whole section on what functionality to
>> *ADD* to VACUUM.
>
> Near but not quite off the topic of VACUUM and new features...
>
> I've been thinking about parsing the vacuum output and storing it in
> Postgresql.  All the tuple, page, cpu time, etc... information would
> be inserted into a reasonably flat set of tables.
>
> The benefits I would expect from this are:
>
> * monitoring ability - I could routinely monitor the values in the
> table to warn when vacuum's are failing or reclaimed space has risen
> dramatically.  I find it easier to write and maintain monitoring
> agents that perform SQL queries than ones that need to routinely
> parse log files and coordinate with cron.
>
> * historical perspective on tuple use - which a relatively small
> amount of storage, I could use the vacuum output to get an idea of
> usage levels over time, which is beneficial for planning additional
> capacity
>
> * historical information could theoretically inform the autovacuum,
> though I assume there are better alternatives planned.
>
> * it could cut down on traffic on this list if admin could see
> routine maintenance in a historical context.
>
> Assuming this isn't a fundamentally horrible idea, it would be nice
> if there were ways to do this without parsing the pretty-printed
> vacuum text (ie, callbacks, triggers, guc variable).
>
> I'd like to know if anybody does this already, thinks its a bad
> idea, or can knock me on the noggin with the pg manual and say,
> "it's already there!".

We had someone working on that for a while; I don't think it got to
the point of being something ready to unleash on the world.

I certainly agree that it would be plenty useful to have this sort of
information available.  Having a body of historical information could
lead to having some "more informed" suggestions for heuristics.
-- 
(reverse (concatenate 'string "gro.mca" "@" "enworbbc"))
http://cbbrowne.com/info/unix.html
Bad command. Bad, bad command! Sit! Stay! Staaay... 

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From: William Yu <wyu@talisys.com>
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Subject: Re: 3WARE Card performance boost?
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Steinar H. Gunderson wrote:
> On Wed, Jan 18, 2006 at 01:58:09PM -0800, William Yu wrote:
>> The key is getting a card with the ability to upgrade the onboard ram.
>>
>> Our previous setup was a LSI MegaRAID 320-1 (128MB), 4xRAID10, 
>> fsync=off. Replaced it with a ARC-1170 (1GB) w/ 24x7200RPM SATA2 drives 
>> (split into 3 8-drive RAID6 arrays) and performance for us is through 
>> the ceiling.
> 
> Well, the fact that you went from four to 24 disks would perhaps be a bigger
> factor than the amount of RAM...
> 
> /* Steinar */

Actually no. Our 2xOpteron 244 server is NOT fast enough to drive an 
array this large. That's why we had to split it up into 3 different 
arrays. I tried all different RAID configs and once past about 8 drives, 
I got the same performance no matter what because the CPU was pegged at 
100%. Right now, 2 of the arrays are just mirroring each other because 
we can't seem utilize the performance right now. (Also protects against 
cabling/power supply issues as we're using 3 seperate external enclosures.)

The 1GB RAM is much bigger because it almost completely hides the write 
activity. Looking at iostat while all our jobs are running, there's 
almost no disk activity. If I manually type "sync", I see 1 big 
250MB-500MB write storm for 2 seconds but otherwise, writes just slowly 
dribble out to disk.

From pgsql-performance-owner@postgresql.org  Wed Jan 18 18:48:56 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Michael Riess <mlriess@gmx.de>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum
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On Wed, Jan 18, 2006 at 03:09:42PM +0100, Michael Riess wrote:
> >There's a number of sites that have lots of info on postgresql.conf
> >tuning. Google for 'postgresql.conf tuning' or 'annotated
> >postgresql.conf'.
> 
> I know some of these sites, but who should I know if the information on 
> those pages is correct? The information on those pages should be 
> published as part of the postgres documentation. Doesn't have to be too 
> much, maybe like this page:
> 
> http://www.powerpostgresql.com/Downloads/annotated_conf_80.html
> 
> But it should be part of the documentation to show newbies that not only 
> the information is correct, but also approved of and recommended by the 
> postgres team.

Actually, most of what you find there is probably also found in
techdocs. But of course it would be better if the docs did a better job
of explaining things...
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 18 18:52:58 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Michael Crozier <crozierm@conducivetech.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
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On Wed, Jan 18, 2006 at 11:15:51AM -0800, Michael Crozier wrote:
> I've been thinking about parsing the vacuum output and storing it in 
> Postgresql.  All the tuple, page, cpu time, etc... information would be 
> inserted into a reasonably flat set of tables.
<snip>
> Assuming this isn't a fundamentally horrible idea, it would be nice if there 
> were ways to do this without parsing the pretty-printed vacuum text (ie, 
> callbacks, triggers, guc variable).

The best way to do this would be to modify the vacuum code itself, but
the issue is that vacuum (or at least lazyvacuum) doesn't handle
transactions like the rest of the backend does, so I suspect that there
would be some issues with trying to log the information from the same
backend that was running the vacuum.

> I'd like to know if anybody does this already, thinks its a bad idea, or can 
> knock me on the noggin with the pg manual and say, "it's already there!".

I think it's a good idea, but you should take a look at the recently
added functionality that allows you to investigate the contests of the
FSM via a user function (this is either in 8.1 or in HEAD; I can't
remember which).
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 18 19:02:30 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Marcos <mjs_ops@gmx.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Simple Question of Performance ILIKE or Lower
Message-ID: <20060118230230.GZ17896@pervasive.com>
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On Wed, Jan 18, 2006 at 09:10:30AM +0000, Marcos wrote:
> Hi,
> 
> I have a simple question about performance using two resources.
> 
> What's have the best performance?
> 
> lower( col1 ) LIKE lower( 'myquestion%' )
> 
> OR
> 
> col1 ILIKE 'myquestion%'

If you index lower( col1 ), then the former would likely perform better
(if the optimizer knows it could use the index in that case). Otherwise
I suspect they'd be the same.

Try it and find out.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 18 19:05:32 2006
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To: "Joshua D. Drake" <jd@commandprompt.com>
Cc: Benjamin Arai <barai@cs.ucr.edu>, pgsql-performance@postgresql.org
Subject: Re: 3WARE Card performance boost?
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On Wed, Jan 18, 2006 at 10:24:17AM -0800, Joshua D. Drake wrote:
> Because 3ware does not make a midrange card that has a battery backed 
> cache :). That is the only reason. 3ware makes good stuff.

Why worry about battery-backup if he's running with fsync off?
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Wed Jan 18 19:36:06 2006
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From: Michael Crozier <crozierm@conducivetech.com>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
Date: Wed, 18 Jan 2006 15:36:04 -0800
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On Wednesday 18 January 2006 14:52 pm, Jim C. Nasby wrote:
> I think it's a good idea, but you should take a look at the recently
> added functionality that allows you to investigate the contests of the
> FSM via a user function (this is either in 8.1 or in HEAD; I can't
> remember which).

I will look at this when time allows.  Perhaps there is a combination of 
triggers on stat tables and asynchronous notifications that would provide 
this functionality without getting too deep into the vacuum's transaction 
logic?

Were it too integrated with the vacuum, it would likely be too much for 
contrib/, I assume.


thanks,

  Michael


From pgsql-performance-owner@postgresql.org  Wed Jan 18 19:41:32 2006
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From: Michael Crozier <crozierm@conducivetech.com>
To: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
Date: Wed, 18 Jan 2006 15:41:33 -0800
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> We had someone working on that for a while; I don't think it got to
> the point of being something ready to unleash on the world.

Interesting.  I will dig around the mailing list archives too see how they 
went about it... for my own curiosity if nothing else.   If you happen to 
know offhand, I'd appreciate a link.

Regards,

 Michael

From pgsql-performance-owner@postgresql.org  Wed Jan 18 19:44:40 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Michael Crozier <crozierm@conducivetech.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
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On Wed, Jan 18, 2006 at 03:36:04PM -0800, Michael Crozier wrote:
> 
> On Wednesday 18 January 2006 14:52 pm, Jim C. Nasby wrote:
> > I think it's a good idea, but you should take a look at the recently
> > added functionality that allows you to investigate the contests of the
> > FSM via a user function (this is either in 8.1 or in HEAD; I can't
> > remember which).
> 
> I will look at this when time allows.  Perhaps there is a combination of 
> triggers on stat tables and asynchronous notifications that would provide 
> this functionality without getting too deep into the vacuum's transaction 
> logic?

You can't put triggers on system tables, at least not ones that will be
triggered by system operations themselves, because the backend bypasses
normal access methods. Also, most of the really interesting info isn't
logged anywhere in a system table; stuff like the amount of dead space,
tuples removed, etc.

> Were it too integrated with the vacuum, it would likely be too much for 
> contrib/, I assume.

Probably.

A good alternative might be allowing vacuum to output some
machine-friendly information (maybe into a backend-writable file?) and
then have code that could load that into a table (though presumably that
could should be as simple as just a COPY).
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Thu Jan 19 06:49:04 2006
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Subject: Re: Use of Stored Procedures and
From: Marcos <mjs_ops@gmx.net>
To: Michael Fuhr <mike@fuhr.org>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <20060118202825.GA94306@winnie.fuhr.org>
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	<20060118202825.GA94306@winnie.fuhr.org>
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> What statements?  

Sorry. Statements is my code.

> What problem are you trying to solve?

I want know how I make to use a prepared plan
( http://www.postgresql.org/docs/8.1/static/sql-prepare.html ). I read
that I need to use the SPI_PREPARE and SPI_EXEC in my code, but I didn't
understand how make it.

Thanks


From pgsql-performance-owner@postgresql.org  Thu Jan 19 07:48:07 2006
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Subject: Re: Use of Stored Procedures and
From: Marcos <mjs_ops@gmx.net>
To: Markus Schaber <schabi@logix-tt.com>
Cc: Michael Fuhr <mike@fuhr.org>, pgsql-performance@postgresql.org
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> Which interface are you using to connect to PostgreSQL? libpq, libpqxx,
> pgjdbc, python-popy?
> 
> E. G. PGJDBC handles prepared plans transparently by using the
> PreparedStatement class.
> 
> If you use command line PSQL, you can use the PREPARE commands.

I'm using the adodb to call the stored procedure (plpgsql).

Thanks..


From pgsql-performance-owner@postgresql.org  Thu Jan 19 07:15:12 2006
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Subject: Re: Use of Stored Procedures and
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Hi, Marcos,

Marcos wrote:

>>What problem are you trying to solve?
> 
> I want know how I make to use a prepared plan
> ( http://www.postgresql.org/docs/8.1/static/sql-prepare.html ). I read
> that I need to use the SPI_PREPARE and SPI_EXEC in my code, but I didn't
> understand how make it.

Which interface are you using to connect to PostgreSQL? libpq, libpqxx,
pgjdbc, python-popy?

E. G. PGJDBC handles prepared plans transparently by using the
PreparedStatement class.

If you use command line PSQL, you can use the PREPARE commands.

Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Thu Jan 19 08:20:59 2006
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To: Marcos <mjs_ops@gmx.net>, pgsql-performance@postgresql.org
Subject: Re: Use of Stored Procedures and
References: <1137488693.971.23.camel@servidor>	
	<20060118202825.GA94306@winnie.fuhr.org>
	<1137660256.930.7.camel@servidor>	 <43CF74BD.7000100@logix-tt.com>
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Hi, Marcos,

Marcos wrote:
>>Which interface are you using to connect to PostgreSQL? libpq, libpqxx,
>>pgjdbc, python-popy?
>>
>>E. G. PGJDBC handles prepared plans transparently by using the
>>PreparedStatement class.
>>
>>If you use command line PSQL, you can use the PREPARE commands.
> 
> I'm using the adodb to call the stored procedure (plpgsql).

So your statements are inside a plpgsql stored procedure, important to
know that.

AFAIK, plpgsql uses prepared statements internally, so it should not be
necessary to use them explicitly.

Markus
-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Thu Jan 19 13:38:20 2006
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From: "Benjamin Arai" <barai@cs.ucr.edu>
To: <pgsql-performance@postgresql.org>
Subject: Stored Procedures
Date: Thu, 19 Jan 2006 09:38:01 -0800
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Hi,
 
Will simple queries such as "SELECT * FROM blah_table WHERE tag='x'; work
any faster by putting them into a stored procedure?
 
Benjamin Arai
barai@cs.ucr.edu
http://www.benjaminarai.com <http://www.benjaminarai.com/> 
 

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<BODY>
<DIV><SPAN class=3D856473617-19012006><FONT face=3DArial=20
size=3D2>Hi,</FONT></SPAN></DIV>
<DIV><SPAN class=3D856473617-19012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D856473617-19012006><FONT face=3DArial size=3D2>Will =
simple queries=20
such as "SELECT * FROM blah_table WHERE tag=3D'x'; work any faster by =
putting them=20
into a stored procedure?</FONT></SPAN></DIV>
<DIV><SPAN class=3D856473617-19012006><FONT face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D856473617-19012006><FONT face=3DArial size=3D2>
<DIV align=3Dleft><FONT face=3DArial><STRONG>Benjamin =
Arai</STRONG></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"mailto:barai@cs.ucr.edu">barai@cs.ucr.edu</A></FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2><A=20
href=3D"http://www.benjaminarai.com/">http://www.benjaminarai.com</A></FO=
NT></DIV>
<DIV align=3Dleft><FONT face=3DArial=20
size=3D2></FONT>&nbsp;</DIV></FONT></SPAN></DIV></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Thu Jan 19 16:04:39 2006
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Date: Thu, 19 Jan 2006 20:34:26 +0100
From: Andreas Kretschmer <akretschmer@spamfence.net>
To: pgsql-performance@postgresql.org
Subject: Re: Stored Procedures
Message-ID: <20060119193426.GA5403@kaufbach.delug.de>
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Benjamin Arai <barai@cs.ucr.edu> schrieb:

> Hi,
>  
> Will simple queries such as "SELECT * FROM blah_table WHERE tag='x'; work any
> faster by putting them into a stored procedure?

IMHO no, why do you think so? You can use PREPARE instead, if you have many
selects like this.


HTH, Andreas
-- 
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect.                              (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly."    (unknow)
Kaufbach, Saxony, Germany, Europe.              N 51.05082�, E 13.56889�

From pgsql-performance-owner@postgresql.org  Thu Jan 19 17:38:36 2006
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From: Vivek Khera <vivek@khera.org>
Subject: Re: 3WARE Card performance boost?
Date: Thu, 19 Jan 2006 16:38:33 -0500
To: Postgresql Performance <pgsql-performance@postgresql.org>
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On Jan 18, 2006, at 1:09 PM, Benjamin Arai wrote:

> Obviously, I have done this to improve write performance for the  
> update each
> week.  My question is if I install a 3ware or similar card to  
> replace my

I'll bet that if you increase your checkpoint_segments (and  
corresponding timeout value) to something in the 10's or higher it  
will help you a lot.


From pgsql-performance-owner@postgresql.org  Thu Jan 19 18:20:27 2006
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Subject: query plans different for 8.1 on windows and aix
Date: Thu, 19 Jan 2006 17:20:22 -0500
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From: "Tim Jones" <TJones@optio.com>
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Hi,
=20
  I am trying to perform the following type of query  'select
patientname ... from patient were patientname LIKE 'JONES%, %' order by
patientname asc limit 100'. There about 1.4 million rows in the table.
On my windows machine (2GB Ram ,3Ghz, Windows XP, 120GB Hard Drive,
postgres 8.1beta4) it takes about 150 millisecs and the query plan is=20
=20
    'Limit  (cost=3D18381.90..18384.40 rows=3D100 width=3D404)'
'  ->  Unique  (cost=3D18381.90..18418.62 rows=3D1469 width=3D404)'
'        ->  Sort  (cost=3D18381.90..18385.57 rows=3D1469 width=3D404)'
'              Sort Key: patientname, patientidentifier,
patientvipindicator, patientconfidentiality, patientmrn,
patientfacility, patientssn, patientsex, patientbirthdate'
'              ->  Bitmap Heap Scan on patient  (cost=3D81.08..18304.62
rows=3D1469 width=3D404)'
'                    Filter: ((patientname)::text ~~ ''BILL%,
%''::text)'
'                    ->  Bitmap Index Scan on ix_patientname
(cost=3D0.00..81.08 rows=3D7347 width=3D0)'
'                          Index Cond: (((patientname)::text >=3D
''BILL''::character varying) AND ((patientname)::text <
''BILM''::character varying))'

However the same query on AIX (4 1.5Ghz processors, 60GB filesystem, 4GB
Ram, postgres 8.1.2) it takes like 5 secs because the query plan just
uses sequentials scans
=20
Limit  (cost=3D100054251.96..100054253.41 rows=3D58 width=3D161)
   ->  Unique  (cost=3D100054251.96..100054253.41 rows=3D58 width=3D161)
         ->  Sort  (cost=3D100054251.96..100054252.11 rows=3D58 =
width=3D161)
               Sort Key: patientname, patientidentifier,
patientvipindicator, patientconfidentiality, patientmrn,
patientfacility, patientssn, patientsex, patientbirthdate
               ->  Seq Scan on patient  =
(cost=3D100000000.00..100054250.26
rows=3D58 width=3D161)
                     Filter: ((patientname)::text ~~ 'SMITH%,
NA%'::text)

Why is postgres using a sequential scan and not the index what
parameters do I need to adjust
=20
thanks
Tim Jones
Optio Software

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<BODY>
<DIV><FONT face=3DArial size=3D2>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006>Hi,</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D052055021-19012006>&nbsp; =
I am trying=20
to perform the following type of&nbsp;query&nbsp; 'select patientname =
... from=20
patient were patientname LIKE 'JONES%, %' order by patientname asc limit =
100'.=20
There about 1.4 million rows in the table. On my windows machine (2GB =
Ram ,3Ghz,=20
Windows XP, 120GB Hard Drive, postgres 8.1beta4) it takes about 150 =
millisecs=20
and the query plan is </SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN =
class=3D052055021-19012006>&nbsp;&nbsp;&nbsp;=20
'Limit&nbsp; (cost=3D18381.90..18384.40 rows=3D100 =
width=3D404)'<BR>'&nbsp;=20
-&gt;&nbsp; Unique&nbsp; (cost=3D18381.90..18418.62 rows=3D1469=20
width=3D404)'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&gt;&nbsp; =

Sort&nbsp; (cost=3D18381.90..18385.57 rows=3D1469=20
width=3D404)'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;=20
Sort Key: patientname, patientidentifier, patientvipindicator,=20
patientconfidentiality, patientmrn, patientfacility, patientssn, =
patientsex,=20
patientbirthdate'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Bitmap Heap Scan on patient&nbsp; (cost=3D81.08..18304.62 =
rows=3D1469=20
width=3D404)'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Filter: ((patientname)::text ~~ ''BILL%,=20
%''::text)'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Bitmap Index Scan on ix_patientname&nbsp; =
(cost=3D0.00..81.08=20
rows=3D7347=20
width=3D0)'<BR>'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
p;&nbsp;&nbsp;&nbsp;=20
Index Cond: (((patientname)::text &gt;=3D ''BILL''::character varying) =
AND=20
((patientname)::text &lt; ''BILM''::character =
varying))'<BR></SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN =
class=3D052055021-19012006>However the same=20
query on AIX (4 1.5Ghz processors, 60GB filesystem, 4GB Ram, postgres =
8.1.2) it=20
takes like 5 secs because the query plan just uses sequentials=20
scans</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN =
class=3D052055021-19012006>Limit&nbsp;=20
(cost=3D100054251.96..100054253.41 rows=3D58 =
width=3D161)<BR>&nbsp;&nbsp; -&gt;&nbsp;=20
Unique&nbsp; (cost=3D100054251.96..100054253.41 rows=3D58=20
width=3D161)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
-&gt;&nbsp;=20
Sort&nbsp; (cost=3D100054251.96..100054252.11 rows=3D58=20
width=3D161)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Sort Key: patientname, patientidentifier, patientvipindicator,=20
patientconfidentiality, patientmrn, patientfacility, patientssn, =
patientsex,=20
patientbirthdate<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
-&gt;&nbsp; Seq Scan on patient&nbsp; (cost=3D100000000.00..100054250.26 =
rows=3D58=20
width=3D161)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
Filter: ((patientname)::text ~~ 'SMITH%, =
NA%'::text)<BR></SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D052055021-19012006>Why is =
postgres=20
using a sequential scan and not the index what parameters do I need to=20
adjust</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D052055021-19012006>thanks</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D052055021-19012006>Tim=20
Jones</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D052055021-19012006>Optio=20
Software</DIV></SPAN></FONT></FONT></DIV></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Thu Jan 19 18:27:36 2006
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To: "Tim Jones" <TJones@optio.com>
cc: pgsql-performance@postgresql.org
Subject: Re: query plans different for 8.1 on windows and aix 
In-reply-to: <47668A1334CDBF46927C1A0DFEB223D3033ACE@mail.optiosoftware.com> 
References: <47668A1334CDBF46927C1A0DFEB223D3033ACE@mail.optiosoftware.com>
Comments: In-reply-to "Tim Jones" <TJones@optio.com>
	message dated "Thu, 19 Jan 2006 17:20:22 -0500"
Date: Thu, 19 Jan 2006 17:27:35 -0500
Message-ID: <9909.1137709655@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Tim Jones" <TJones@optio.com> writes:
> Why is postgres using a sequential scan and not the index what
> parameters do I need to adjust

You probably initialized the AIX database in a non-C locale.
See the manual concerning LIKE index optimizations.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Thu Jan 19 18:52:55 2006
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Subject: Re: Stable function being evaluated more than once in a single
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To: "Jim C. Nasby" <jnasby@pervasive.com>
Date: Thu, 19 Jan 2006 17:52:14 -0500 (EST)
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Here is updated documentation for STABLE.  I just changed a few words
for clarification.

---------------------------------------------------------------------------

Jim C. Nasby wrote:
> Adding -docs...
> 
> On Fri, Jan 13, 2006 at 07:27:28PM -0500, Tom Lane wrote:
> > "Jim C. Nasby" <jnasby@pervasive.com> writes:
> > > Is the issue that the optimizer won't combine two function calls (ie:
> > > SELECT foo(..) ... WHERE foo(..)), or is it that sometimes it won't make
> > > the optimization (maybe depending on the query plan, for example)?
> > 
> > What the STABLE category actually does is give the planner permission to
> > use the function within an indexscan qualification, eg,
> > 	WHERE indexed_column = f(42)
> > Since an indexscan involves evaluating the comparison expression just
> > once and using its value to search the index, this would be incorrect
> > if the expression's value might change from row to row.  (For VOLATILE
> > functions, we assume that the correct behavior is the naive SQL
> > semantics of actually computing the WHERE clause at each candidate row.)
> > 
> > There is no function cache and no checking for duplicate expressions.
> > I think we do check for duplicate aggregate expressions, but not
> > anything else.
>  
> In that case I'd say that the sSTABLE section of 32.6 should be changed
> to read:
> 
> A STABLE function cannot modify the database and is guaranteed to
> return the same results given the same arguments for all calls within a
> single surrounding query. This category gives the planner permission to
> use the function within an indexscan qualification. (Since an indexscan
> involves evaluating the comparison expression just once and using its
> value to search the index, this would be incorrect if the expression's
> value might change from row to row.) There is no function cache and no
> checking for duplicate expressions.
> 
> I can provide a patch to that effect if it's easier...
> 
> On a related note, would it be difficult to recognize multiple calls of
> the same function in one query? ISTM that would be a win for all but the
> most trivial of functions...
> -- 
> Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
> Pervasive Software      http://pervasive.com    work: 512-231-6117
> vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 1: if posting/reading through Usenet, please send an appropriate
>        subscribe-nomail command to majordomo@postgresql.org so that your
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> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

--ELM1137711134-28690-0_
Content-Transfer-Encoding: 7bit
Content-Type: text/plain
Content-Disposition: inline; filename="/bjm/diff"

Index: doc/src/sgml/xfunc.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v
retrieving revision 1.109
diff -c -c -r1.109 xfunc.sgml
*** doc/src/sgml/xfunc.sgml	29 Nov 2005 01:46:54 -0000	1.109
--- doc/src/sgml/xfunc.sgml	19 Jan 2006 22:43:58 -0000
***************
*** 899,911 ****
       <para>
        A <literal>STABLE</> function cannot modify the database and is
        guaranteed to return the same results given the same arguments
!       for all calls within a single surrounding query.  This category
!       allows the optimizer to optimize away multiple calls of the function
!       within a single query.  In particular, it is safe to use an expression
!       containing such a function in an index scan condition.  (Since an
!       index scan will evaluate the comparison value only once, not once at
!       each row, it is not valid to use a <literal>VOLATILE</> function in
!       an index scan condition.)
       </para>
      </listitem>
      <listitem>
--- 899,911 ----
       <para>
        A <literal>STABLE</> function cannot modify the database and is
        guaranteed to return the same results given the same arguments
!       for all rows within a single statement. This category allows the
!       optimizer to optimize multiple calls of the function to a single
!       call. In particular, it is safe to use an expression containing
!       such a function in an index scan condition. (Since an index scan
!       will evaluate the comparison value only once, not once at each
!       row, it is not valid to use a <literal>VOLATILE</> function in an
!       index scan condition.)
       </para>
      </listitem>
      <listitem>

--ELM1137711134-28690-0_--

From pgsql-performance-owner@postgresql.org  Thu Jan 19 18:54:35 2006
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Date: Thu, 19 Jan 2006 17:54:32 -0500
From: Alex Turner <armtuk@gmail.com>
To: William Yu <wyu@talisys.com>
Subject: Re: 3WARE Card performance boost?
Cc: pgsql-performance@postgresql.org
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He's talking about RAID 1 here, not a gargantuan RAID 6.  Onboard RAM
on the controller card is going to make very little difference.  All
it will do is allow the card to re-order writes to a point (not all
cards even do this).

Alex.

On 1/18/06, William Yu <wyu@talisys.com> wrote:
> Benjamin Arai wrote:
> > Obviously, I have done this to improve write performance for the update
> > each week.  My question is if I install a 3ware or similar card to
> > replace my current software RAID 1 configuration, am I going to see a
> > very large improvement?  If so, what would be a ball park figure?
>
> The key is getting a card with the ability to upgrade the onboard ram.
>
> Our previous setup was a LSI MegaRAID 320-1 (128MB), 4xRAID10,
> fsync=3Doff. Replaced it with a ARC-1170 (1GB) w/ 24x7200RPM SATA2 drives
> (split into 3 8-drive RAID6 arrays) and performance for us is through
> the ceiling.
>
> For OLTP type updates, we've gotten about +80% increase. For massive
> 1-statement updates, performance increase is in the +triple digits.
>
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From pgsql-performance-owner@postgresql.org  Thu Jan 19 19:10:43 2006
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Date: Fri, 20 Jan 2006 12:10:32 +1300
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Autovacuum / full vacuum (off-topic?)
In-reply-to: <20060118225257.GY17896@pervasive.com>
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Jim C. Nasby wrote:

> 
> I think it's a good idea, but you should take a look at the recently
> added functionality that allows you to investigate the contests of the
> FSM via a user function (this is either in 8.1 or in HEAD; I can't
> remember which).

AFAICS it is still in the patch queue for 8.2.

It's called 'pg_freespacemap' and is available for 8.1/8.0 from the 
Pgfoundry 'backports' project:

http://pgfoundry.org/projects/backports

Cheers

Mark


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Verified.  I am working toward getting all those patches applied.

---------------------------------------------------------------------------

Mark Kirkwood wrote:
> Jim C. Nasby wrote:
> 
> > 
> > I think it's a good idea, but you should take a look at the recently
> > added functionality that allows you to investigate the contests of the
> > FSM via a user function (this is either in 8.1 or in HEAD; I can't
> > remember which).
> 
> AFAICS it is still in the patch queue for 8.2.
> 
> It's called 'pg_freespacemap' and is available for 8.1/8.0 from the 
> Pgfoundry 'backports' project:
> 
> http://pgfoundry.org/projects/backports
> 
> Cheers
> 
> Mark
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 1: if posting/reading through Usenet, please send an appropriate
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> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-performance-owner@postgresql.org  Fri Jan 20 00:39:27 2006
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Date: Fri, 20 Jan 2006 12:35:36 +0800
To: pgsql-performance@postgresql.org
From: K C Lau <kclau60@netvigator.com>
Subject: SELECT MIN, MAX took longer time than SELECT COUNT, MIN, MAX
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The following query took 17 seconds:
select count(LogSN), min(LogSN), max(LogSN) from Log where create_time < 
'2005/10/19';

Figuring that getting the count will involve scanning the database, I took 
it out, but the new query took 200 seconds:
select min(LogSN), max(LogSN) from Log where create_time < '2005/10/19';

Is it because the planner is using index pk_log instead of idx_logtime? 
Anyway to avoid that?

I can get instant replies with 2 separate queries for min(LogSN) and 
max(LogSN) using order by create_time limit 1, but I can't get both values 
within 1 query using the limit 1 construct. Any suggestions?

I am running pg 8.1.2 on Windows 2000. The queries are done immediately 
after a vacuum analyze.

Best regards,
KC.

----------------------

esdt=> \d log;
  create_time | character varying(23)   | default 
'1970/01/01~00:00:00.000'::char
acter varying
  logsn       | integer                 | not null
  ...
Indexes:
     "pk_log" PRIMARY KEY, btree (logsn)
     "idx_logtime" btree (create_time, logsn)
     ...

esdt=> vacuum analyze log;
VACUUM

esdt=> explain analyze select count(LogSN), min(LogSN), max(LogSN) from Log 
where create_time < '2005/10/19';

  Aggregate  (cost=57817.74..57817.75 rows=1 width=4) (actual 
time=17403.381..17403.384 rows=1 loops=1)
    ->  Bitmap Heap Scan on log  (cost=1458.31..57172.06 rows=86089 
width=4) (actual time=180.368..17039.262 rows=106708 loops=1)
          Recheck Cond: ((create_time)::text < '2005/10/19'::text)
          ->  Bitmap Index Scan on idx_logtime  (cost=0.00..1458.31 
rows=86089 width=0) (actual time=168.777..168.777 rows=106708 loops=1)
                Index Cond: ((create_time)::text < '2005/10/19'::text)
  Total runtime: 17403.787 ms

esdt=> explain analyze select min(LogSN), max(LogSN) from Log where 
create_time < '2005/10/19';

  Result  (cost=2.51..2.52 rows=1 width=0) (actual 
time=200051.507..200051.510 rows=1 loops=1)
    InitPlan
      ->  Limit  (cost=0.00..1.26 rows=1 width=4) (actual 
time=18.541..18.544 rows=1 loops=1)
            ->  Index Scan using pk_log on log  (cost=0.00..108047.11 
rows=86089
width=4) (actual time=18.533..18.533 rows=1 loops=1)
                  Filter: (((create_time)::text < '2005/10/19'::text) AND 
(logsn IS NOT NULL))
      ->  Limit  (cost=0.00..1.26 rows=1 width=4) (actual 
time=200032.928..200032.931 rows=1 loops=1)
            ->  Index Scan Backward using pk_log on 
log  (cost=0.00..108047.11 rows=86089 width=4) (actual 
time=200032.920..200032.920 rows=1 loops=1)
                  Filter: (((create_time)::text < '2005/10/19'::text) AND 
(logsn IS NOT NULL))
  Total runtime: 200051.701 ms

esdt=> explain analyze select LogSN from Log where create_time < 
'2005/10/19' order by create_time limit 1;

  Limit  (cost=0.00..0.98 rows=1 width=31) (actual time=0.071..0.073 rows=1 
loops=1)
    ->  Index Scan using idx_logtime on log  (cost=0.00..84649.94 
rows=86089 width=31) (actual time=0.063..0.063 rows=1 loops=1)
          Index Cond: ((create_time)::text < '2005/10/19'::text)
  Total runtime: 0.182 ms

esdt=> explain analyze select LogSN from Log where create_time < 
'2005/10/19' order by create_time desc limit 1;
  Limit  (cost=0.00..0.98 rows=1 width=31) (actual time=0.058..0.061 rows=1 
loops=1)
    ->  Index Scan Backward using idx_logtime on log  (cost=0.00..84649.94 
rows=86089 width=31) (actual time=0.051..0.051 rows=1 loops=1)
          Index Cond: ((create_time)::text < '2005/10/19'::text)
  Total runtime: 0.186 ms


From pgsql-performance-owner@postgresql.org  Fri Jan 20 05:14:17 2006
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To: pgsql-performance@postgresql.org
Subject: Retaining execution plans between connections?
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Hi there,

I am running a website where each page connects to the DB to retrieve and
write information. Each page load uses a separate connection (rather than
just sharing one as is the common case) because I use a lot of transactions=
.

I am looking to speed up performance, and since each page executes a static
set of queries where only the parameters change, I was hoping to take
advantage of stored procedures since I read that PostgreSQL's caches the
execution plans used inside stored procedures.

However, the documentation states that this execution plan caching is done
on a per-connection basis. If each page uses a separate connection, I can
get no performance benefit between pages.

In other words, there's no benefit to me in putting a one-shot query that i=
s
basically the same for every page (e.g. "SELECT * FROM users WHERE
user_name=3D'<username>'") inside a stored proc, since the generated execut=
ion
plan will be thrown away once the connection is dropped.

Has anyone found a way around this limitation? As I said, I can't share the
DB connection between pages (unless someone knows of a way to do this and
still retain a level of separation between pages that use the same DB
connection).

Many thanks,

James

------=_Part_2395_31688086.1137748455547
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

Hi there,<br>
<br>
I am running a website where each page connects to the DB to retrieve
and write information. Each page load uses a separate connection
(rather than just sharing one as is the common case) because I use a
lot of transactions.<br>
<br>
I am looking to speed up performance, and since each page executes a
static set of queries where only the parameters change, I was hoping to
take advantage of stored procedures since I read that PostgreSQL's
caches the execution plans used inside stored procedures.<br>
<br>
However, the documentation states that this execution plan caching is
done on a per-connection basis. If each page uses a separate
connection, I can get no performance benefit between pages.<br>
<br>
In other words, there's no benefit to me in putting a one-shot query
that is basically the same for every page (e.g. &quot;SELECT * FROM users
WHERE user_name=3D'&lt;username&gt;'&quot;) inside a stored proc, since the
generated execution plan will be thrown away once the connection is
dropped.<br>
<br>
Has anyone found a way around this limitation? As I said, I can't share
the DB connection between pages (unless someone knows of a way to do
this and still retain a level of separation between pages that use the
same DB connection).<br>
<br>
Many thanks,<br>
<br>
James<br>

------=_Part_2395_31688086.1137748455547--

From pgsql-performance-owner@postgresql.org  Fri Jan 20 05:35:50 2006
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Date: Fri, 20 Jan 2006 15:05:49 +0530
From: Pandurangan R S <pandurangan.r.s@gmail.com>
To: James Russell <internationalhobo@gmail.com>
Subject: Re: Retaining execution plans between connections?
Cc: pgsql-performance@postgresql.org
In-Reply-To: <3a3a16930601200114p27ccb3fdn750286898f39c405@mail.gmail.com>
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you could use pgpool

http://pgpool.projects.postgresql.org/


On 1/20/06, James Russell <internationalhobo@gmail.com> wrote:
> Hi there,
>
>  I am running a website where each page connects to the DB to retrieve an=
d
> write information. Each page load uses a separate connection (rather than
> just sharing one as is the common case) because I use a lot of transactio=
ns.
>
>  I am looking to speed up performance, and since each page executes a sta=
tic
> set of queries where only the parameters change, I was hoping to take
> advantage of stored procedures since I read that PostgreSQL's caches the
> execution plans used inside stored procedures.
>
>  However, the documentation states that this execution plan caching is do=
ne
> on a per-connection basis. If each page uses a separate connection, I can
> get no performance benefit between pages.
>
>  In other words, there's no benefit to me in putting a one-shot query tha=
t
> is basically the same for every page (e.g. "SELECT * FROM users WHERE
> user_name=3D'<username>'") inside a stored proc, since the generated exec=
ution
> plan will be thrown away once the connection is dropped.
>
>  Has anyone found a way around this limitation? As I said, I can't share =
the
> DB connection between pages (unless someone knows of a way to do this and
> still retain a level of separation between pages that use the same DB
> connection).
>
>  Many thanks,
>
>  James
>

From pgsql-general-owner@postgresql.org  Fri Jan 20 10:07:41 2006
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From: Stephan Vollmer <svollmer@gmx.de>
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Subject: Creation of tsearch2 index is very slow
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Hello!

I noticed that the creation of a GIST index for tsearch2 takes very
long - about 20 minutes. CPU utilization is 100 %, the resulting
index file size is ~25 MB. Is this behaviour normal?

Full text columns:   title          author_list
tsearch2 word lists: fti_title      fti_author_list
tsearch2 indexes:    idx_fti_title  idx_fti_author_list

The table has 700,000 records. When I create a normal B-Tree index
on the same column for testing purposes, it works quite fast
(approx. 30 seconds).

The columns that should be indexed are small, only about 10 words on
average.

System specs:
Athlon64 X2 3800+, 2 GB RAM
PostgreSQL 8.1.2, Windows XP SP2

I've never noticed this problem before, so could it probably be
related to v8.1.2? Or is something in my configuration or table
definition that causes this sluggishness?

Thanks very much in advance for your help!

- Stephan



This is the table definition:
-----------------------------------------------------------------
CREATE TABLE publications
(
  id int4 NOT NULL DEFAULT nextval('publications_id_seq'::regclass),
  publication_type_id int4 NOT NULL DEFAULT 0,
  keyword text NOT NULL,
  mdate date,
  "year" date,
  title text,
  fti_title tsvector,
  author_list text,
  fti_author_list tsvector,
  overview_timestamp timestamp,
  overview_xml text,
  CONSTRAINT publications_pkey PRIMARY KEY (keyword) USING INDEX
      TABLESPACE dblp_index,
  CONSTRAINT publications_publication_type_id_fkey FOREIGN KEY
     (publication_type_id)
      REFERENCES publication_types (id) MATCH SIMPLE
      ON UPDATE RESTRICT ON DELETE RESTRICT,
  CONSTRAINT publications_year_check CHECK (date_part('month'::text,
"year") =3D 1::double precision AND date_part('day'::text, "year") =3D
1::double precision)
)
WITHOUT OIDS;

CREATE INDEX fki_publications_publication_type_id
  ON publications
  USING btree
  (publication_type_id)
  TABLESPACE dblp_index;

CREATE INDEX idx_fti_author_list
  ON publications
  USING gist
  (fti_author_list)
  TABLESPACE dblp_index;

CREATE INDEX idx_fti_title
  ON publications
  USING gist
  (fti_title)
  TABLESPACE dblp_index;

CREATE INDEX idx_publications_year
  ON publications
  USING btree
  ("year")
  TABLESPACE dblp_index;

CREATE INDEX idx_publications_year_part
  ON publications
  USING btree
  (date_part('year'::text, "year"))
  TABLESPACE dblp_index;


CREATE TRIGGER tsvectorupdate_all
  BEFORE INSERT OR UPDATE
  ON publications
  FOR EACH ROW
  EXECUTE PROCEDURE multi_tsearch2();



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PS:

What I forgot to mention was that inserting records into the table
is also about 2-3 times slower than before (most likely due to the
slow index update operations).

I dropped the whole database and restored the dumpfile, but the
result it the same. When the index is recreated after COPYing the
data, it takes more than 20 minutes for _each_ of both tsearch2
indexes. So the total time to restore this table is more than 45
minutes!

- Stephan


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From pgsql-performance-owner@postgresql.org  Fri Jan 20 11:14:54 2006
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Subject: Re: Retaining execution plans between connections?
From: Neil Conway <neilc@samurai.com>
To: James Russell <internationalhobo@gmail.com>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <3a3a16930601200114p27ccb3fdn750286898f39c405@mail.gmail.com>
References: <3a3a16930601200114p27ccb3fdn750286898f39c405@mail.gmail.com>
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Date: Fri, 20 Jan 2006 10:14:59 -0500
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On Fri, 2006-01-20 at 18:14 +0900, James Russell wrote:
> I am looking to speed up performance, and since each page executes a
> static set of queries where only the parameters change, I was hoping
> to take advantage of stored procedures since I read that PostgreSQL's
> caches the execution plans used inside stored procedures.

Note that you can also take advantage of plan caching by using prepared
statements (PREPARE, EXECUTE and DEALLOCATE). These are also session
local, however (i.e. you can't share prepared statements between
connections).

> As I said, I can't share the DB connection between pages (unless
> someone knows of a way to do this and still retain a level of
> separation between pages that use the same DB connection).

You can't share plans among different sessions at the moment. Can you
elaborate on why you can't use persistent or pooled database
connections?

-Neil



From pgsql-general-owner@postgresql.org  Fri Jan 20 11:35:21 2006
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To: Stephan Vollmer <svollmer@gmx.de>
cc: pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow 
In-reply-to: <43D0ED57.1020608@gmx.de> 
References: <43D0ED57.1020608@gmx.de>
Comments: In-reply-to Stephan Vollmer <svollmer@gmx.de>
	message dated "Fri, 20 Jan 2006 15:01:59 +0100"
Date: Fri, 20 Jan 2006 10:35:21 -0500
Message-ID: <17454.1137771321@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Stephan Vollmer <svollmer@gmx.de> writes:
> I noticed that the creation of a GIST index for tsearch2 takes very
> long - about 20 minutes. CPU utilization is 100 %, the resulting
> index file size is ~25 MB. Is this behaviour normal?

This has been complained of before.  GIST is always going to be slower
at index-building than btree; in the btree case there's a simple optimal
strategy for making an index (ie, sort the keys) but for GIST we don't
know anything better to do than insert the keys one at a time.

However, I'm not sure that anyone's tried to do any performance
optimization on the GIST insert code ... there might be some low-hanging
fruit there.  It'd be interesting to look at a gprof profile of what the
backend is doing during the index build.  Do you have the ability to do
that, or would you be willing to give your data to someone else to
investigate with?  (The behavior is very possibly data-dependent, which
is why I want to see a profile with your specific data and not just some
random dataset or other.)

			regards, tom lane

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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200601201619.k0KGJWE19919@candle.pha.pa.us>
Subject: Re: Extremely irregular query performance
In-Reply-To: <1137059321.3180.34.camel@localhost.localdomain>
To: Simon Riggs <simon@2ndquadrant.com>
Date: Fri, 20 Jan 2006 11:19:32 -0500 (EST)
CC: Tom Lane <tgl@sss.pgh.pa.us>, =?ISO-8859-1?Q?Jean-Philippe_C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>, pgsql-performance@postgresql.org
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Simon Riggs wrote:
> On Wed, 2006-01-11 at 22:23 -0500, Tom Lane wrote:
> > =?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> > > Thanks a lot for this info, I was indeed exceeding the genetic
> > > optimizer's threshold.  Now that it is turned off, I get
> > > a very stable response time of 435ms (more or less 5ms) for
> > > the same query. It is about three times slower than the best
> > > I got with the genetic optimizer on, but the overall average
> > > is much lower.
> > 
> > Hmm.  It would be interesting to use EXPLAIN ANALYZE to confirm that the
> > plan found this way is the same as the best plan found by GEQO, and
> > the extra couple hundred msec is the price you pay for the exhaustive
> > plan search.  If GEQO is managing to find a plan better than the regular
> > planner then we need to look into why ...
> 
> It seems worth noting in the EXPLAIN whether GEQO has been used to find
> the plan, possibly along with other factors influencing the plan such as
> enable_* settings.

I thought the best solution would be to replace "QUERY PLAN" with "GEQO
QUERY PLAN" when GEQO was in use.  However, looking at the code, I see
no way to do that cleanly.

Instead, I added documentation to EXPLAIN to highlight the fact the
execution plan will change when GEQO is in use.

(I also removed a documentation mention of the pre-7.3 EXPLAIN output
behavior.)

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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Index: doc/src/sgml/ref/explain.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/ref/explain.sgml,v
retrieving revision 1.35
diff -c -c -r1.35 explain.sgml
*** doc/src/sgml/ref/explain.sgml	4 Jan 2005 00:39:53 -0000	1.35
--- doc/src/sgml/ref/explain.sgml	20 Jan 2006 16:18:53 -0000
***************
*** 151,161 ****
    </para>
  
    <para>
!    Prior to <productname>PostgreSQL</productname> 7.3, the plan was
!    emitted in the form of a <literal>NOTICE</literal> message.  Now it
!    appears as a query result (formatted like a table with a single
!    text column).
    </para>
   </refsect1>
  
   <refsect1>
--- 151,162 ----
    </para>
  
    <para>
!    Genetic query optimization (<acronym>GEQO</acronym>) randomly 
!    tests execution plans.  Therefore, when the number of tables 
!    exceeds <varname>geqo</> and genetic query optimization is in use,
!    the execution plan will change each time the statement is executed.
    </para>
+ 
   </refsect1>
  
   <refsect1>

--ELM1137773972-28690-2_--

From pgsql-performance-owner@postgresql.org  Fri Jan 20 12:35:01 2006
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Simon Riggs <simon@2ndquadrant.com>,
	=?ISO-8859-1?Q?Jean-Philippe_C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>, pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance 
In-reply-to: <200601201619.k0KGJWE19919@candle.pha.pa.us> 
References: <200601201619.k0KGJWE19919@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Fri, 20 Jan 2006 11:19:32 -0500"
Date: Fri, 20 Jan 2006 11:34:49 -0500
Message-ID: <18684.1137774889@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
>     <para>
> !    Genetic query optimization (<acronym>GEQO</acronym>) randomly 
> !    tests execution plans.  Therefore, when the number of tables 
> !    exceeds <varname>geqo</> and genetic query optimization is in use,
> !    the execution plan will change each time the statement is executed.
>     </para>

geqo_threshold, please --- geqo is a boolean.

Possibly better wording:  Therefore, when the number of tables exceeds
geqo_threshold causing genetic query optimization to be used, the
execution plan is likely to change each time the statement is executed.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 12:42:16 2006
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200601201642.k0KGgBS23410@candle.pha.pa.us>
Subject: Re: Extremely irregular query performance
In-Reply-To: <18684.1137774889@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 20 Jan 2006 11:42:11 -0500 (EST)
CC: Simon Riggs <simon@2ndquadrant.com>,
	=?ISO-8859-1?Q?Jean-Philippe_C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>, pgsql-performance@postgresql.org
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Done, and paragraph added to 8.1.X.  (7.3 mention retained for 8.1.X.)

---------------------------------------------------------------------------

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >     <para>
> > !    Genetic query optimization (<acronym>GEQO</acronym>) randomly 
> > !    tests execution plans.  Therefore, when the number of tables 
> > !    exceeds <varname>geqo</> and genetic query optimization is in use,
> > !    the execution plan will change each time the statement is executed.
> >     </para>
> 
> geqo_threshold, please --- geqo is a boolean.
> 
> Possibly better wording:  Therefore, when the number of tables exceeds
> geqo_threshold causing genetic query optimization to be used, the
> execution plan is likely to change each time the statement is executed.
> 
> 			regards, tom lane
> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Fri Jan 20 12:48:52 2006
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Date: Fri, 20 Jan 2006 17:49:53 +0100
From: Stephan Vollmer <svollmer@gmx.de>
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To: pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow
References: <43D0ED57.1020608@gmx.de> <17454.1137771321@sss.pgh.pa.us>
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Tom Lane wrote:
> Stephan Vollmer <svollmer@gmx.de> writes:
>> I noticed that the creation of a GIST index for tsearch2 takes very
>> long - about 20 minutes. CPU utilization is 100 %, the resulting
>> index file size is ~25 MB. Is this behaviour normal?
>=20
> This has been complained of before.  GIST is always going to be slower
> at index-building than btree; in the btree case there's a simple optima=
l
> strategy for making an index (ie, sort the keys) but for GIST we don't
> know anything better to do than insert the keys one at a time.

Ah, ok. That explains a lot, although I wonder why it is so much slower.


> However, I'm not sure that anyone's tried to do any performance
> optimization on the GIST insert code ... there might be some low-hangin=
g
> fruit there.  It'd be interesting to look at a gprof profile of what th=
e
> backend is doing during the index build.  Do you have the ability to do=

> that, or would you be willing to give your data to someone else to
> investigate with?

Unfortunately, I'm not able to investigate it further myself as I'm
quite a Postgres newbie. But I could provide someone else with the
example table. Maybe someone else could find out why it is so slow.

I dropped all unnecessary columns and trimmed the table down to
235,000 rows. The dumped table (compressed with RAR) is 7,1 MB. I
don't have a website to upload it but I could send it to someone via
e-mail.

With this 235,000 row table, index creation times are:
- GIST    347063 ms
- B-Tree    2515 ms


Thanks for your help!

- Stephan



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From pgsql-general-owner@postgresql.org  Fri Jan 20 13:05:04 2006
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From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 10:35:21AM -0500, Tom Lane wrote:
> However, I'm not sure that anyone's tried to do any performance
> optimization on the GIST insert code ... there might be some low-hanging
> fruit there.  It'd be interesting to look at a gprof profile of what the
> backend is doing during the index build.  Do you have the ability to do
> that, or would you be willing to give your data to someone else to
> investigate with?  (The behavior is very possibly data-dependent, which
> is why I want to see a profile with your specific data and not just some
> random dataset or other.)

The cost on inserting would generally go to either penalty, or
picksplit. Certainly if you're inserting lots of values in a short
interval, I can imagine picksplit being nasty, since the algorithms for
a lot of datatypes are not really reknown for their speed.

I'm wondering if you could possibly improve the process by grouping
into larger blocks. For example, pull out enough tuples to cover 4
pages and then call picksplit three times to split it into the four
pages. This gives you 4 entries for the level above the leaves. Keep
reading tuples and splitting until you get enough for the next level
and call picksplit on those. etc etc.

The thing is, you never call penalty here so it's questionable whether
the tree will be as efficient as just inserting. For example, if have a
data type representing ranges (a,b), straight inserting can produce the
perfect tree order like a b-tree (assuming non-overlapping entries).
The above process will produce something close, but not quite...

Should probably get out a pen-and-paper to model this. After all, if
the speed of the picksplit increases superlinearly to the number of
elements, calling it will larger sets may prove to be a loss overall...

Perhaps the easiest would be to allow datatypes to provide a bulkinsert
function, like b-tree does? The question is, what should be its input
and output?

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From pgsql-general-owner@postgresql.org  Fri Jan 20 13:09:18 2006
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To: Stephan Vollmer <svollmer@gmx.de>
cc: pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow 
In-reply-to: <43D114B1.5030802@gmx.de> 
References: <43D0ED57.1020608@gmx.de> <17454.1137771321@sss.pgh.pa.us>
	<43D114B1.5030802@gmx.de>
Comments: In-reply-to Stephan Vollmer <svollmer@gmx.de>
	message dated "Fri, 20 Jan 2006 17:49:53 +0100"
Date: Fri, 20 Jan 2006 12:09:13 -0500
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Stephan Vollmer <svollmer@gmx.de> writes:
> Unfortunately, I'm not able to investigate it further myself as I'm
> quite a Postgres newbie. But I could provide someone else with the
> example table. Maybe someone else could find out why it is so slow.

I'd be willing to take a look, if you'll send me the dump file off-list.

> I dropped all unnecessary columns and trimmed the table down to
> 235,000 rows. The dumped table (compressed with RAR) is 7,1 MB. I
> don't have a website to upload it but I could send it to someone via
> e-mail.

Don't have RAR --- gzip or bzip2 is fine ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 13:12:17 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Mark Kirkwood <markir@paradise.net.nz>
Cc: Michael Crozier <crozierm@conducivetech.com>,
	pgsql-performance@postgresql.org
Subject: Re: Autovacuum / full vacuum (off-topic?)
Message-ID: <20060120171214.GE20182@pervasive.com>
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	<034701c61c46$f427df20$f20214ac@bite.lt>
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BTW, given all the recent discussion about vacuuming and our MVCC,
http://www.pervasive-postgres.com/lp/newsletters/2006/Insights_Postgres_Jan.asp#3
should prove interesting. :)
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-general-owner@postgresql.org  Fri Jan 20 13:14:40 2006
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To: Martijn van Oosterhout <kleptog@svana.org>
cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow 
In-reply-to: <20060120170452.GC31908@svana.org> 
References: <43D0ED57.1020608@gmx.de> <17454.1137771321@sss.pgh.pa.us>
	<20060120170452.GC31908@svana.org>
Comments: In-reply-to Martijn van Oosterhout <kleptog@svana.org>
	message dated "Fri, 20 Jan 2006 18:04:52 +0100"
Date: Fri, 20 Jan 2006 12:14:35 -0500
Message-ID: <25127.1137777275@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Martijn van Oosterhout <kleptog@svana.org> writes:
> The cost on inserting would generally go to either penalty, or
> picksplit. Certainly if you're inserting lots of values in a short
> interval, I can imagine picksplit being nasty, since the algorithms for
> a lot of datatypes are not really reknown for their speed.

Tut tut ... in the words of the sage, it is a capital mistake to
theorize in advance of the data.  You may well be right, but on the
other hand it could easily be something dumb like an O(N^2) loop over
a list structure.

I'll post some gprof numbers after Stephan sends me the dump.  We
should probably move the thread to someplace like pgsql-perform, too.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 13:20:30 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: K C Lau <kclau60@netvigator.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: SELECT MIN, MAX took longer time than SELECT COUNT, MIN, MAX
Message-ID: <20060120172026.GF20182@pervasive.com>
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On Fri, Jan 20, 2006 at 12:35:36PM +0800, K C Lau wrote:

Here's the problem... the estimate for the backwards index scan is *way*
off:

>      ->  Limit  (cost=0.00..1.26 rows=1 width=4) (actual 
> time=200032.928..200032.931 rows=1 loops=1)
>            ->  Index Scan Backward using pk_log on 
> log  (cost=0.00..108047.11 rows=86089 width=4) (actual 
> time=200032.920..200032.920 rows=1 loops=1)
>                  Filter: (((create_time)::text < '2005/10/19'::text) AND 
> (logsn IS NOT NULL))
>  Total runtime: 200051.701 ms

BTW, these queries below are meaningless; they are not equivalent to
min(logsn).

> esdt=> explain analyze select LogSN from Log where create_time < 
> '2005/10/19' order by create_time limit 1;
> 
>  Limit  (cost=0.00..0.98 rows=1 width=31) (actual time=0.071..0.073 rows=1 
> loops=1)
>    ->  Index Scan using idx_logtime on log  (cost=0.00..84649.94 
> rows=86089 width=31) (actual time=0.063..0.063 rows=1 loops=1)
>          Index Cond: ((create_time)::text < '2005/10/19'::text)
>  Total runtime: 0.182 ms
> 
> esdt=> explain analyze select LogSN from Log where create_time < 
> '2005/10/19' order by create_time desc limit 1;
>  Limit  (cost=0.00..0.98 rows=1 width=31) (actual time=0.058..0.061 rows=1 
> loops=1)
>    ->  Index Scan Backward using idx_logtime on log  (cost=0.00..84649.94 
> rows=86089 width=31) (actual time=0.051..0.051 rows=1 loops=1)
>          Index Cond: ((create_time)::text < '2005/10/19'::text)
>  Total runtime: 0.186 ms
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
> 

-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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Jim C. Nasby wrote:
> BTW, given all the recent discussion about vacuuming and our MVCC,
> http://www.pervasive-postgres.com/lp/newsletters/2006/Insights_Postgres_Jan.asp#3
> should prove interesting. :)
>   
Please explain... what is the .asp extension. I have yet to see it 
reliable in production ;)




-- 
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From pgsql-performance-owner@postgresql.org  Fri Jan 20 13:34:09 2006
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On Fri, Jan 20, 2006 at 09:31:14AM -0800, Joshua D. Drake wrote:
> Jim C. Nasby wrote:
> >BTW, given all the recent discussion about vacuuming and our MVCC,
> >http://www.pervasive-postgres.com/lp/newsletters/2006/Insights_Postgres_Jan.asp#3
> >should prove interesting. :)
> >  
> Please explain... what is the .asp extension. I have yet to see it 
> reliable in production ;)

I lay no claim to our infrastructure. :)
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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> I lay no claim to our infrastructure. :)
>   
Can I quote the: Pervasive Senior Engineering Consultant on that?

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From pgsql-performance-owner@postgresql.org  Fri Jan 20 13:44:20 2006
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On Fri, Jan 20, 2006 at 09:37:50AM -0800, Joshua D. Drake wrote:
> 
> >I lay no claim to our infrastructure. :)
> >  
> Can I quote the: Pervasive Senior Engineering Consultant on that?

Sure... I've never been asked to consult on our stuff, and in any case,
I don't do web front-ends (one of the nice things about working with a
team of other consultants). AFAIK IIS will happily talk to PostgreSQL
(though maybe I'm wrong there...)

I *have* asked what database is being used on the backend though, and
depending on the answer to that some folks might have some explaining to
do. :)

*grabs big can of dog food*
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 20 13:47:05 2006
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Subject: Re: Autovacuum / full vacuum (off-topic?)
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> Sure... I've never been asked to consult on our stuff, and in any case,
> I don't do web front-ends (one of the nice things about working with a
> team of other consultants). AFAIK IIS will happily talk to PostgreSQL
> (though maybe I'm wrong there...)

iis (yeah, asp in a successfull productive environement hehe) & postgresql 
works even better for us than iis & mssql :-)

- thomas 



From pgsql-performance-owner@postgresql.org  Fri Jan 20 14:32:40 2006
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Date: Fri, 20 Jan 2006 19:32:34 +0100
From: Antoine <melser.anton@gmail.com>
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Subject: query stopped working after tables > 50000 records
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Hi,
I have a query that does a left outer join. The query gets some text 
from a reference table where one of the query's main tables may or may 
not have the text's tables id. It wasn't super fast, but now it simply 
won't execute. It won't complete either through odbc or via pgadmin 
(haven't yet tried via psql). A week ago (with considerably fewer 
records in the main table) it executed fine, not particularly quickly, 
but not that slowly either. Now it locks up postgres completely (if 
nothing else needs anything it takes 100% cpu), and even after an hour 
gives me nothing. I have come up with a solution that gets the text via 
another query (possibly even a better solution), but this seems very 
strange.
Can anyone shed some light on the subject? I tried a full vacuum on the 
tables that needed it, and a postgres restart, all to no avail.
Cheers
Antoine
ps. I can send the query if that will help...
pps. running a home-compiled 8.1.1 with tables in the query having 70000 
records, 30000 records and 10 for the outer join. Without the left outer 
join it runs in ~ 1 second.

From pgsql-performance-owner@postgresql.org  Fri Jan 20 14:51:25 2006
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Date: Fri, 20 Jan 2006 19:50:23 +0100
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Subject: Re: [PERFORMANCE] Stored Procedures
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>>Hi,
>>  
>> Will simple queries such as "SELECT * FROM blah_table WHERE tag='x'; work any
>> faster by putting them into a stored procedure?

>
>IMHO no, why do you think so? You can use PREPARE instead, if you have many
>selects like this.


I tought that creating stored procedures in database means
storing it's execution plan (well, actually storing it like a
compiled object). Well, that's what I've learned couple a years
ago in colledge ;)

What are the advantages of parsing SP functions every time it's called?

My position is that preparing stored procedures for execution solves
more problems, that it creates.
And the most important one to be optimizing access to queries from 
multiple connections (which is one of the most important reasons 
for using stored procedures in the first place).

Best regards,
	Rikard


From pgsql-performance-owner@postgresql.org  Fri Jan 20 14:51:29 2006
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To: "Jim C. Nasby" <jnasby@pervasive.com>
cc: K C Lau <kclau60@netvigator.com>, pgsql-performance@postgresql.org
Subject: Re: SELECT MIN, MAX took longer time than SELECT COUNT, MIN, MAX 
In-reply-to: <20060120172026.GF20182@pervasive.com> 
References: <6.2.1.2.0.20060120120150.08ab7b00@localhost>
	<20060120172026.GF20182@pervasive.com>
Comments: In-reply-to "Jim C. Nasby" <jnasby@pervasive.com>
	message dated "Fri, 20 Jan 2006 11:20:26 -0600"
Date: Fri, 20 Jan 2006 13:51:14 -0500
Message-ID: <25978.1137783074@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Jim C. Nasby" <jnasby@pervasive.com> writes:
> On Fri, Jan 20, 2006 at 12:35:36PM +0800, K C Lau wrote:
> Here's the problem... the estimate for the backwards index scan is *way*
> off:

>> ->  Limit  (cost=0.00..1.26 rows=1 width=4) (actual 
>> time=200032.928..200032.931 rows=1 loops=1)
>> ->  Index Scan Backward using pk_log on 
>> log  (cost=0.00..108047.11 rows=86089 width=4) (actual 
>> time=200032.920..200032.920 rows=1 loops=1)
>> Filter: (((create_time)::text < '2005/10/19'::text) AND 
>> (logsn IS NOT NULL))
>> Total runtime: 200051.701 ms

It's more subtle than you think.  The estimated rowcount is the
estimated number of rows fetched if the indexscan were run to
completion, which it isn't because the LIMIT cuts it off after the
first returned row.  That estimate is not bad (we can see from the
aggregate plan that the true value would have been 106708, assuming
that the "logsn IS NOT NULL" condition isn't filtering anything).

The real problem is that it's taking quite a long time for the scan
to reach the first row with create_time < 2005/10/19, which is not
too surprising if logsn is strongly correlated with create_time ...
but in the absence of any cross-column statistics the planner has
no very good way to know that.  (Hm ... but both of them probably
also show a strong correlation to physical order ... we could look
at that maybe ...)  The default assumption is that the two columns
aren't correlated and so it should not take long to hit the first such
row, which is why the planner likes the indexscan/limit plan.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 14:56:22 2006
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To: pgsql-performance@postgresql.org
Subject: Re: Stored procedures
References: <6.2.1.2.0.20060120120150.08ab7b00@localhost>
	<20060120172026.GF20182@pervasive.com>
	<25978.1137783074@sss.pgh.pa.us>
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>
>> Hi,
>>  
>> Will simple queries such as "SELECT * FROM blah_table WHERE tag='x'; 
>> work any
>> faster by putting them into a stored procedure?

>
> IMHO no, why do you think so? You can use PREPARE instead, if you have 
> many
> selects like this.


I tought that creating stored procedures in database means
storing it's execution plan (well, actually storing it like a
compiled object). Well, that's what I've learned couple a years
ago in colledge ;)

What are the advantages of parsing SP functions every time it's called?

My position is that preparing stored procedures for execution solves
more problems, that it creates.
And the most important one to be optimizing access to queries from 
multiple connections (which is one of the most important reasons for 
using stored procedures in the first place).

Best regards,
    Rikard



From pgsql-performance-owner@postgresql.org  Fri Jan 20 15:02:53 2006
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Subject: Re: Autovacuum / full vacuum (off-topic?)
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On Fri, Jan 20, 2006 at 06:46:45PM +0100, me@alternize.com wrote:
> >Sure... I've never been asked to consult on our stuff, and in any case,
> >I don't do web front-ends (one of the nice things about working with a
> >team of other consultants). AFAIK IIS will happily talk to PostgreSQL
> >(though maybe I'm wrong there...)
> 
> iis (yeah, asp in a successfull productive environement hehe) & postgresql 
> works even better for us than iis & mssql :-)

Just last night I was talking to someone about different databases and
what-not (he's stuck in a windows shop using MSSQL and I mentioned I'd
heard some bad things about it's stability). I realized at some point
that asking about what large installs of something exist is pretty
pointless... given enough effort you can make almost anything scale. As
an example, there's a cable company with a MySQL database that's nearly
1TB... if that's not proof you can make anything scale, I don't know
what is. ;)

What people really need to ask about is how hard it is to make something
work, and how many problems you're likely to keep encountering.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Fri Jan 20 15:04:39 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Antoine <melser.anton@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: query stopped working after tables > 50000 records
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Send query, output of EXPLAIN and table definitions.

On Fri, Jan 20, 2006 at 07:32:34PM +0100, Antoine wrote:
> Hi,
> I have a query that does a left outer join. The query gets some text 
> from a reference table where one of the query's main tables may or may 
> not have the text's tables id. It wasn't super fast, but now it simply 
> won't execute. It won't complete either through odbc or via pgadmin 
> (haven't yet tried via psql). A week ago (with considerably fewer 
> records in the main table) it executed fine, not particularly quickly, 
> but not that slowly either. Now it locks up postgres completely (if 
> nothing else needs anything it takes 100% cpu), and even after an hour 
> gives me nothing. I have come up with a solution that gets the text via 
> another query (possibly even a better solution), but this seems very 
> strange.
> Can anyone shed some light on the subject? I tried a full vacuum on the 
> tables that needed it, and a postgres restart, all to no avail.
> Cheers
> Antoine
> ps. I can send the query if that will help...
> pps. running a home-compiled 8.1.1 with tables in the query having 70000 
> records, 30000 records and 10 for the outer join. Without the left outer 
> join it runs in ~ 1 second.
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Have you searched our list archives?
> 
>               http://archives.postgresql.org
> 

-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Rikard Pavelic <rikard.pavelic@zg.htnet.hr>
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Stored Procedures
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On Fri, Jan 20, 2006 at 07:50:23PM +0100, Rikard Pavelic wrote:
> >>Hi,
> >> 
> >>Will simple queries such as "SELECT * FROM blah_table WHERE tag='x'; work 
> >>any
> >>faster by putting them into a stored procedure?
> 
> >
> >IMHO no, why do you think so? You can use PREPARE instead, if you have many
> >selects like this.
> 
> 
> I tought that creating stored procedures in database means
> storing it's execution plan (well, actually storing it like a
> compiled object). Well, that's what I've learned couple a years
> ago in colledge ;)

My college professor said it, it must be true! ;P

My understanding is that in plpgsql, 'bare' queries get prepared and act
like prepared statements. IE:

SELECT INTO variable
    field
    FROM table
    WHERE condition = true
;

> What are the advantages of parsing SP functions every time it's called?
> 
> My position is that preparing stored procedures for execution solves
> more problems, that it creates.
> And the most important one to be optimizing access to queries from 
> multiple connections (which is one of the most important reasons 
> for using stored procedures in the first place).

Ok, so post some numbers then. It might be interesting to look at the
cost of preparing a statement, although AFAIK that does not store the
query plan anywhere.

In most databases, query planning seems to be a pretty expensive
operation. My experience is that that isn't the case with PostgreSQL.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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To: Martijn van Oosterhout <kleptog@svana.org>
cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow 
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[ thread moved to pgsql-performance ]

I've obtained a gprof profile on Stephan's sample case (many thanks for
providing the data, Stephan).  The command is
	CREATE INDEX foo ON publications_test USING gist (fti_title);
where fti_title is a tsvector column.  There are 236984 rows in the
table, most with between 4 and 10 words in fti_title.
sum(length(fti_title)) yields 1636202 ... not sure if this is a
relevant measure, however.

Using CVS tip with a fairly vanilla configuration (including
--enable-cassert), here are all the hotspots down to the 1% level:

  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 20.19      1.90     1.90   588976     0.00     0.00  gistchoose
 19.02      3.69     1.79   683471     0.00     0.00  XLogInsert
  5.95      4.25     0.56  3575135     0.00     0.00  LWLockAcquire
  4.46      4.67     0.42  3579005     0.00     0.00  LWLockRelease
  4.14      5.06     0.39  3146848     0.00     0.00  AllocSetAlloc
  3.72      5.41     0.35   236984     0.00     0.00  gistdoinsert
  3.40      5.73     0.32   876047     0.00     0.00  hash_search
  2.76      5.99     0.26  3998576     0.00     0.00  LockBuffer
  2.28      6.21     0.22 11514275     0.00     0.00  gistdentryinit
  1.86      6.38     0.18   841757     0.00     0.00  UnpinBuffer
  1.81      6.55     0.17 12201023     0.00     0.00  FunctionCall1
  1.81      6.72     0.17   237044     0.00     0.00  AllocSetCheck
  1.49      6.86     0.14   236984     0.00     0.00  gistmakedeal
  1.49      7.00     0.14 10206985     0.00     0.00  FunctionCall3
  1.49      7.14     0.14  1287874     0.00     0.00  MemoryContextAllocZero
  1.28      7.26     0.12   826179     0.00     0.00  PinBuffer
  1.17      7.37     0.11   875785     0.00     0.00  hash_any
  1.17      7.48     0.11  1857292     0.00     0.00  MemoryContextAlloc
  1.17      7.59     0.11   221466     0.00     0.00  PageIndexTupleDelete
  1.06      7.69     0.10  9762101     0.00     0.00  gistpenalty

Clearly, one thing that would be worth doing is suppressing the WAL
traffic when possible, as we already do for btree builds.  It seems
that gistchoose may have some internal ineffiency too --- I haven't
looked at the code yet.  The other thing that jumps out is the very
large numbers of calls to gistdentryinit, FunctionCall1, FunctionCall3.
Some interesting parts of the calls/calledby graph are:

-----------------------------------------------
                0.35    8.07  236984/236984      gistbuildCallback [14]
[15]    89.5    0.35    8.07  236984         gistdoinsert [15]
                0.14    3.55  236984/236984      gistmakedeal [16]
                1.90    0.89  588976/588976      gistchoose [17]
                0.07    0.83  825960/841757      ReadBuffer [19]
                0.09    0.10  825960/1287874     MemoryContextAllocZero [30]
                0.12    0.05 1888904/3998576     LockBuffer [29]
                0.13    0.00  825960/3575135     LWLockAcquire [21]
                0.10    0.00  825960/3579005     LWLockRelease [26]
                0.06    0.00  473968/3146848     AllocSetAlloc [27]
                0.03    0.00  473968/1857292     MemoryContextAlloc [43]
                0.02    0.00  825960/1272423     gistcheckpage [68]
-----------------------------------------------
                0.14    3.55  236984/236984      gistdoinsert [15]
[16]    39.2    0.14    3.55  236984         gistmakedeal [16]
                1.20    0.15  458450/683471      XLogInsert [18]
                0.01    0.66  224997/224997      gistxlogInsertCompletion [20]
                0.09    0.35  444817/444817      gistgetadjusted [23]
                0.08    0.17  456801/456804      formUpdateRdata [32]
                0.17    0.01  827612/841757      UnpinBuffer [35]
                0.11    0.00  221466/221466      PageIndexTupleDelete [42]
                0.02    0.08  456801/460102      gistfillbuffer [45]
                0.06    0.04    1649/1649        gistSplit [46]
                0.08    0.00  685099/3579005     LWLockRelease [26]
                0.03    0.05  446463/446463      gistFindCorrectParent [50]
                0.04    0.02  685099/3998576     LockBuffer [29]
                0.04    0.00    1649/1649        gistextractbuffer [58]
                0.03    0.00  460102/460121      write_buffer [66]
                0.02    0.00  825960/826092      ReleaseBuffer [69]
                0.02    0.00  221402/221402      gistadjscans [82]
                0.00    0.00    1582/1582        gistunion [131]
                0.00    0.00    1649/1649        formSplitRdata [147]
                0.00    0.00    1649/1649        gistjoinvector [178]
                0.00    0.00       3/3           gistnewroot [199]
                0.00    0.00  458450/461748      gistnospace [418]
                0.00    0.00  458450/458450      WriteNoReleaseBuffer [419]
                0.00    0.00    1652/1671        WriteBuffer [433]
-----------------------------------------------
                1.90    0.89  588976/588976      gistdoinsert [15]
[17]    29.7    1.90    0.89  588976         gistchoose [17]
                0.25    0.17 9762101/10892174     FunctionCall3 <cycle 1> [38]
                0.18    0.14 9762101/11514275     gistdentryinit [28]
                0.10    0.00 9762101/9762101     gistpenalty [47]
                0.04    0.02  588976/1478610     gistDeCompressAtt [39]
-----------------------------------------------
                0.00    0.00       1/683471      gistbuild [12]
                0.00    0.00       1/683471      log_heap_update [273]
                0.00    0.00       1/683471      RecordTransactionCommit [108]
                0.00    0.00       1/683471      smgrcreate [262]
                0.00    0.00       3/683471      gistnewroot [199]
                0.00    0.00       5/683471      heap_insert [116]
                0.00    0.00      12/683471      _bt_insertonpg [195]
                0.59    0.07  224997/683471      gistxlogInsertCompletion [20]
                1.20    0.15  458450/683471      gistmakedeal [16]
[18]    21.4    1.79    0.22  683471         XLogInsert [18]
                0.11    0.00  683471/3575135     LWLockAcquire [21]
                0.08    0.00  687340/3579005     LWLockRelease [26]
                0.03    0.00  683471/683471      GetCurrentTransactionIdIfAny [65]
                0.01    0.00   15604/15604       AdvanceXLInsertBuffer [111]
                0.00    0.00       3/10094       BufferGetBlockNumber [95]
                0.00    0.00    3869/3870        XLogWrite [281]
                0.00    0.00    3870/3871        LWLockConditionalAcquire [428]
                0.00    0.00       3/3           BufferGetFileNode [611]
-----------------------------------------------
                0.00    0.00    3164/11514275     gistunion [131]
                0.01    0.00  270400/11514275     gistSplit [46]
                0.03    0.02 1478610/11514275     gistDeCompressAtt [39]
                0.18    0.14 9762101/11514275     gistchoose [17]
[28]     4.0    0.22    0.16 11514275         gistdentryinit [28]
                0.16    0.00 11514275/12201023     FunctionCall1 [36]
-----------------------------------------------
                0.00    0.00      67/12201023     index_endscan <cycle 1> [167]
                0.01    0.00  686681/12201023     gistcentryinit [62]
                0.16    0.00 11514275/12201023     gistdentryinit [28]
[36]     1.8    0.17    0.00 12201023         FunctionCall1 [36]
                0.00    0.00      67/67          btendscan [231]
                0.00    0.00 12200956/22855929     data_start [414]
-----------------------------------------------
                                  67             index_beginscan_internal <cycle 1> [169]
                0.01    0.01  444817/10892174     gistgetadjusted [23]
                0.25    0.17 9762101/10892174     gistchoose [17]
[38]     1.5    0.14    0.00 10206985         FunctionCall3 <cycle 1> [38]
                0.00    0.00 10206918/22855929     data_start [414]
                0.00    0.00      67/67          btbeginscan [486]
                                  67             RelationGetIndexScan <cycle 1> [212]

Now that we have some data, we can start to think about how to improve
matters ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 15:39:44 2006
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To: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Stored Procedures
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	<20060120191031.GO20182@pervasive.com>
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Jim C. Nasby wrote:
> My college professor said it, it must be true! ;P
>
>   
The famous joke ;)
> My understanding is that in plpgsql, 'bare' queries get prepared and act
> like prepared statements. IE:
>
> SELECT INTO variable
>     field
>     FROM table
>     WHERE condition = true
> ;
>
>   
Unfortunately I don't know enough about PostgreSQL, but from responses 
I've been reading I've
come to that conclusion.
> Ok, so post some numbers then. It might be interesting to look at the
> cost of preparing a statement, although AFAIK that does not store the
> query plan anywhere.
>
> In most databases, query planning seems to be a pretty expensive
> operation. My experience is that that isn't the case with PostgreSQL.
>   

I didn't think about storing query plan anywhere on the disk, rather 
keep them in memory pool.
It would be great if we had an option to use prepare statement for 
stored procedure so it
would prepare it self the first time it's called and remained prepared 
until server shutdown or
memory pool overflow.

This would solve problems with prepare which is per session, so for 
prepared function to be
optimal one must use same connection.

From pgsql-performance-owner@postgresql.org  Fri Jan 20 16:10:44 2006
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From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 02:14:29PM -0500, Tom Lane wrote:
> [ thread moved to pgsql-performance ]
>=20
> I've obtained a gprof profile on Stephan's sample case (many thanks for
> providing the data, Stephan).  The command is

<snip>

Something I'm missing is the calls to tsearch functions. I'm not 100%
familiar with gprof, but is it possible those costs have been added
somewhere else because it's in a shared library? Perhaps the costs went
into FunctionCall1/3?

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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To: Martijn van Oosterhout <kleptog@svana.org>
cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow 
In-reply-to: <20060120201036.GE31908@svana.org> 
References: <43D0ED57.1020608@gmx.de> <17454.1137771321@sss.pgh.pa.us>
	<20060120170452.GC31908@svana.org> <26153.1137784469@sss.pgh.pa.us>
	<20060120201036.GE31908@svana.org>
Comments: In-reply-to Martijn van Oosterhout <kleptog@svana.org>
	message dated "Fri, 20 Jan 2006 21:10:36 +0100"
Date: Fri, 20 Jan 2006 15:21:45 -0500
Message-ID: <26583.1137788505@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Martijn van Oosterhout <kleptog@svana.org> writes:
> Something I'm missing is the calls to tsearch functions. I'm not 100%
> familiar with gprof, but is it possible those costs have been added
> somewhere else because it's in a shared library? Perhaps the costs went
> into FunctionCall1/3?

I think that the tsearch functions must be the stuff charged as
"data_start" (which is not actually any symbol in our source code).
That is showing as being called by FunctionCallN which is what you'd
expect.

If the totals given by gprof are correct, then it's down in the noise.
I don't think I trust that too much ... but I don't see anything in the
gprof manual about how to include a dynamically loaded library in the
profile.  (I did compile tsearch2 with -pg, but that's evidently not
enough.)

I'll see if I can link tsearch2 statically to resolve this question.

			regards, tom lane

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From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 03:21:45PM -0500, Tom Lane wrote:
> If the totals given by gprof are correct, then it's down in the noise.
> I don't think I trust that too much ... but I don't see anything in the
> gprof manual about how to include a dynamically loaded library in the
> profile.  (I did compile tsearch2 with -pg, but that's evidently not
> enough.)

There is some mention on the web of an environment variable you can
set: LD_PROFILE=3D<libname>

These pages seem relevent:
http://sourceware.org/ml/binutils/2002-04/msg00047.html
http://www.scit.wlv.ac.uk/cgi-bin/mansec?1+gprof

It's wierd how some man pages for gprof describe this feature, but the
one on my local system doesn't mention it.

> I'll see if I can link tsearch2 statically to resolve this question.

That'll work too...
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From pgsql-performance-owner@postgresql.org  Fri Jan 20 17:19:20 2006
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To: Martijn van Oosterhout <kleptog@svana.org>
cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow 
In-reply-to: <20060120205132.GF31908@svana.org> 
References: <43D0ED57.1020608@gmx.de> <17454.1137771321@sss.pgh.pa.us>
	<20060120170452.GC31908@svana.org> <26153.1137784469@sss.pgh.pa.us>
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	<20060120205132.GF31908@svana.org>
Comments: In-reply-to Martijn van Oosterhout <kleptog@svana.org>
	message dated "Fri, 20 Jan 2006 21:51:32 +0100"
Date: Fri, 20 Jan 2006 16:19:15 -0500
Message-ID: <26958.1137791955@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Well, I feel like a fool, because I failed to notice that the total
runtime shown in that profile wasn't anywhere close to the actual wall
clock time.  gprof is indeed simply not counting the time spent in
dynamically-linked code.  With tsearch2 statically linked into the
backend, a more believable picture emerges:

  %   cumulative   self              self     total           
 time   seconds   seconds    calls  Ks/call  Ks/call  name    
 98.96   1495.93  1495.93 33035195     0.00     0.00  hemdistsign
  0.27   1500.01     4.08 10030581     0.00     0.00  makesign
  0.11   1501.74     1.73   588976     0.00     0.00  gistchoose
  0.10   1503.32     1.58   683471     0.00     0.00  XLogInsert
  0.05   1504.15     0.83   246579     0.00     0.00  sizebitvec
  0.05   1504.93     0.78   446399     0.00     0.00  gtsvector_union
  0.03   1505.45     0.52  3576475     0.00     0.00  LWLockRelease
  0.03   1505.92     0.47     1649     0.00     0.00  gtsvector_picksplit
  0.03   1506.38     0.47  3572572     0.00     0.00  LWLockAcquire
  0.02   1506.74     0.36   444817     0.00     0.00  gtsvector_same
  0.02   1507.09     0.35  4077089     0.00     0.00  AllocSetAlloc
  0.02   1507.37     0.28   236984     0.00     0.00  gistdoinsert
  0.02   1507.63     0.26   874195     0.00     0.00  hash_search
  0.02   1507.89     0.26  9762101     0.00     0.00  gtsvector_penalty
  0.01   1508.08     0.19   236984     0.00     0.00  gistmakedeal
  0.01   1508.27     0.19   841754     0.00     0.00  UnpinBuffer
  0.01   1508.45     0.18 22985469     0.00     0.00  hemdistcache
  0.01   1508.63     0.18  3998572     0.00     0.00  LockBuffer
  0.01   1508.81     0.18   686681     0.00     0.00  gtsvector_compress
  0.01   1508.98     0.17 11514275     0.00     0.00  gistdentryinit

So we gotta fix hemdistsign ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 17:35:17 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Rikard Pavelic <rikard.pavelic@zg.htnet.hr>
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Stored Procedures
Message-ID: <20060120213455.GT20182@pervasive.com>
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On Fri, Jan 20, 2006 at 08:38:23PM +0100, Rikard Pavelic wrote:
> This would solve problems with prepare which is per session, so for 
> prepared function to be
> optimal one must use same connection.

If you're dealing with something that's performance critical you're not
going to be constantly re-connecting anyway, so I don't see what the
issue is.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 04:19:15PM -0500, Tom Lane wrote:
>   %   cumulative   self              self     total          =20
>  time   seconds   seconds    calls  Ks/call  Ks/call  name   =20
>  98.96   1495.93  1495.93 33035195     0.00     0.00  hemdistsign

<snip>

> So we gotta fix hemdistsign ...

lol! Yeah, I guess so. Pretty nasty loop. LOOPBIT will iterate 8*63=3D504
times and it's going to do silly bit handling on each and every
iteration.

Given that all it's doing is counting bits, a simple fix would be to
loop over bytes, use XOR and count ones. For extreme speedup create a
lookup table with 256 entries to give you the answer straight away...

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From pgsql-performance-owner@postgresql.org  Fri Jan 20 17:57:23 2006
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	Fri, 20 Jan 2006 16:42:20 -0500
To: pgsql-performance@postgresql.org
Subject: Sudden slowdown of Pg server 
From: Jerry Sievers <jerry@jerrysievers.com>
Date: 20 Jan 2006 16:42:20 -0500
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Hello;  

I am going through a post mortem analysis of an infrequent but
recurring problem on a Pg 8.0.3 installation.  Application code
connects to Pg using J2EE pooled connections.

 PostgreSQL 8.0.3 on sparc-sun-solaris2.9, compiled by GCC sparc-sun-solaris2.8-gcc (GCC) 3.3.2

Database is quite large with respect to the number of tables, some of
which have up to 6 million tuples.  Typical idle/busy connection ratio
is 3/100 but occationally we'll catch 20 or more busy sessions.

The problem manifests itself and appears like a locking issue.  About
weekly throuput slows down and we notice the busy connection count
rising minute by minute.  2, 20, 40...  Before long, the app server
detects lack of responsiveness and fails over to another app server
(not Pg) which in turn attempts a bunch of new connections into
Postgres.

Sampling of the snapshots of pg_locks and pg_stat_activity tables
takes place each minute.

I am wishing for a few new ideas as to what to be watching; Here's
some observations that I've made.

1. At no time do any UN-granted locks show in pg_locks
2. The number of exclusive locks is small 1, 4, 8
3. Other locks type/mode are numerous but appear like normal workload.
4. There are at   least a few old '<IDLE> In Transaction' cases in
   activity view
5. No interesting error messages or warning in Pg logs.
6. No crash of Pg backend

Other goodies includes a bounty of poor performing queries which are
constantly being optimized now for good measure.  Aside from the heavy
queries, performance is generallly decent.

Resource related server configs have been boosted substantially but
have not undergone any formal R&D to verify that we're inthe safe
under heavy load.

An max_fsm_relations setting which is *below* our table and index
count was discovered by me today and will be increased this evening
during a maint cycle.

The slowdown and subsequent run-away app server takes place within a
small 2-5 minute window and I have as of yet not been able to get into
Psql during the event for a hands-on look.

Questions;

1. Is there any type of resource lock that can unconditionally block
   another session and NOT appear as UN-granted lock?

2. What in particular other runtime info would be most useful to
   sample here?

3. What Solaris side runtime stats might give some clues here
   (maybe?)( and how often to sample?  Assume needs to be aggressive
   due to how fast this problem crops up.

Any help appreciated

Thank you


-- 
-------------------------------------------------------------------------------
Jerry Sievers   305 854-3001 (home)     WWW ECommerce Consultant
                305 321-1144 (mobile	http://www.JerrySievers.com/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 17:44:03 2006
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Date: Fri, 20 Jan 2006 22:44:02 +0100
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Message-ID: <20060120214402.GA22493@uio.no>
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On Fri, Jan 20, 2006 at 10:37:54PM +0100, Martijn van Oosterhout wrote:
> Given that all it's doing is counting bits, a simple fix would be to
> loop over bytes, use XOR and count ones. For extreme speedup create a
> lookup table with 256 entries to give you the answer straight away...

For extra obfscation:

  unsigned v = (unsigned)c;
  int num_bits = (v * 0x1001001001001ULL & 0x84210842108421ULL) % 0x1f;

(More more-or-less intelligent options at
http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetNaive :-) )

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 17:50:32 2006
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To: Martijn van Oosterhout <kleptog@svana.org>
cc: Stephan Vollmer <svollmer@gmx.de>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow 
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Comments: In-reply-to Martijn van Oosterhout <kleptog@svana.org>
	message dated "Fri, 20 Jan 2006 22:37:54 +0100"
Date: Fri, 20 Jan 2006 16:50:17 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Martijn van Oosterhout <kleptog@svana.org> writes:
> Given that all it's doing is counting bits, a simple fix would be to
> loop over bytes, use XOR and count ones. For extreme speedup create a
> lookup table with 256 entries to give you the answer straight away...

Yeah, I just finished doing that and got about a 20x overall speedup
(30-some seconds to build the index instead of 10 minutes).  However,
hemdistsign is *still* 70% of the runtime after doing that.  The problem
seems to be that gtsvector_picksplit is calling it an inordinate number
of times:

                0.53   30.02    1649/1649        FunctionCall2 <cycle 2> [19]
[20]    52.4    0.53   30.02    1649         gtsvector_picksplit [20]
               29.74    0.00 23519673/33035195     hemdistsign [18]
                0.14    0.00 22985469/22985469     hemdistcache [50]
                0.12    0.00  268480/10030581     makesign [25]
                0.02    0.00  270400/270400      fillcache [85]
                0.00    0.00    9894/4077032     AllocSetAlloc [34]
                0.00    0.00    9894/2787477     MemoryContextAlloc [69]

(hemdistcache calls hemdistsign --- I think gprof is doing something
funny with tail-calls here, and showing hemdistsign as directly called
from gtsvector_picksplit when control really arrives through hemdistcache.)

The bulk of the problem is clearly in this loop, which performs O(N^2)
comparisons to find the two entries that are furthest apart in hemdist
terms:

    for (k = FirstOffsetNumber; k < maxoff; k = OffsetNumberNext(k))
    {
        for (j = OffsetNumberNext(k); j <= maxoff; j = OffsetNumberNext(j))
        {
            if (k == FirstOffsetNumber)
                fillcache(&cache[j], GETENTRY(entryvec, j));

            size_waste = hemdistcache(&(cache[j]), &(cache[k]));
            if (size_waste > waste)
            {
                waste = size_waste;
                seed_1 = k;
                seed_2 = j;
            }
        }
    }

I wonder if there is a way to improve on that.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 18:14:24 2006
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Date: Fri, 20 Jan 2006 17:13:58 -0500
From: "Jignesh K. Shah" <J.K.Shah@Sun.COM>
Subject: Re: Sudden slowdown of Pg server
In-reply-to: <m3r772tw3n.fsf@prod01.jerrysievers.com>
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lockstat is available in Solaris 9. That can help you to determine if 
there are any kernel level locks that are occuring during that time.
Solaris 10 also has plockstat which can be used to identify userland 
locks happening in your process.

Since you have Solaris 9, try the following:

You can run (as root)
lockstat sleep 5 
and note the output which can be long.

I guess "prstat -am" output, "iostat -xczn 3", "vmstat 3" outputs will 
help also.

prstat -am has a column called "LAT", if the value is in double digits, 
then you have a locking issue which will probably result in higher "SLP" 
value for the process.  (Interpretation is data and workload specific 
which this email is too small to decode)

Once you have identified a particular process (if any) to be the source 
of the problem, get its id and you can look at the outputs of following 
command which (quite intrusive)
truss -c -p $pid   2> truss-syscount.txt

(Ctrl-C after a while to stop collecting)

truss -a -e -u":::" -p $pid 2> trussout.txt

(Ctrl-C after a while to stop collecting)

Regards,
Jignesh


Jerry Sievers wrote:

>Hello;  
>
>I am going through a post mortem analysis of an infrequent but
>recurring problem on a Pg 8.0.3 installation.  Application code
>connects to Pg using J2EE pooled connections.
>
> PostgreSQL 8.0.3 on sparc-sun-solaris2.9, compiled by GCC sparc-sun-solaris2.8-gcc (GCC) 3.3.2
>
>Database is quite large with respect to the number of tables, some of
>which have up to 6 million tuples.  Typical idle/busy connection ratio
>is 3/100 but occationally we'll catch 20 or more busy sessions.
>
>The problem manifests itself and appears like a locking issue.  About
>weekly throuput slows down and we notice the busy connection count
>rising minute by minute.  2, 20, 40...  Before long, the app server
>detects lack of responsiveness and fails over to another app server
>(not Pg) which in turn attempts a bunch of new connections into
>Postgres.
>
>Sampling of the snapshots of pg_locks and pg_stat_activity tables
>takes place each minute.
>
>I am wishing for a few new ideas as to what to be watching; Here's
>some observations that I've made.
>
>1. At no time do any UN-granted locks show in pg_locks
>2. The number of exclusive locks is small 1, 4, 8
>3. Other locks type/mode are numerous but appear like normal workload.
>4. There are at   least a few old '<IDLE> In Transaction' cases in
>   activity view
>5. No interesting error messages or warning in Pg logs.
>6. No crash of Pg backend
>
>Other goodies includes a bounty of poor performing queries which are
>constantly being optimized now for good measure.  Aside from the heavy
>queries, performance is generallly decent.
>
>Resource related server configs have been boosted substantially but
>have not undergone any formal R&D to verify that we're inthe safe
>under heavy load.
>
>An max_fsm_relations setting which is *below* our table and index
>count was discovered by me today and will be increased this evening
>during a maint cycle.
>
>The slowdown and subsequent run-away app server takes place within a
>small 2-5 minute window and I have as of yet not been able to get into
>Psql during the event for a hands-on look.
>
>Questions;
>
>1. Is there any type of resource lock that can unconditionally block
>   another session and NOT appear as UN-granted lock?
>
>2. What in particular other runtime info would be most useful to
>   sample here?
>
>3. What Solaris side runtime stats might give some clues here
>   (maybe?)( and how often to sample?  Assume needs to be aggressive
>   due to how fast this problem crops up.
>
>Any help appreciated
>
>Thank you
>
>
>  
>

From pgsql-performance-owner@postgresql.org  Fri Jan 20 18:16:54 2006
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Date: Fri, 20 Jan 2006 23:16:55 +0100
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> I wonder if there is a way to improve on that.

Ooh, the farthest pair problem (in an N-dimensional vector space, though).
I'm pretty sure problems like this has been studied quite extensively in the
literature, although perhaps not with the same norm. It's known under both
"farthest pair" and "diameter", and probably others. I'm fairly sure it
should be solvable in at least O(n log n).

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 18:29:55 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>,pgsql-performance@postgresql.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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At 05:16 PM 1/20/2006, Steinar H. Gunderson wrote:
>On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> > I wonder if there is a way to improve on that.
>
>Ooh, the farthest pair problem (in an N-dimensional vector space, though).
>I'm pretty sure problems like this has been studied quite extensively in the
>literature, although perhaps not with the same norm. It's known under both
>"farthest pair" and "diameter", and probably others. I'm fairly sure it
>should be solvable in at least O(n log n).

If the N-dimensional space is Euclidean (any <x, x+1> is the same 
distance apart in dimension x), then finding the farthest pair can be 
done in at least O(n).

If you do not want the actual distance and can create the proper data 
structures, particularly if you can update them incrementally as you 
generate pairs, it is often possible to solve this problem in O(lg n) or O(1).

I'll do some grinding.
Ron 



From pgsql-performance-owner@postgresql.org  Fri Jan 20 18:33:38 2006
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Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> (hemdistcache calls hemdistsign --- I think gprof is doing something
> funny with tail-calls here, and showing hemdistsign as directly called
> from gtsvector_picksplit when control really arrives through hemdistcache=
=2E)

It may be the compiler. All these functions are declared static, which
gives the compiler quite a bit of leeway to rearrange code.

> The bulk of the problem is clearly in this loop, which performs O(N^2)
> comparisons to find the two entries that are furthest apart in hemdist
> terms:

Ah. A while ago someone came onto the list asking about bit strings
indexing[1]. If I'd known tsearch worked like this I would have pointed
him to it. Anyway, before he went off to implement it he mentioned
"Jarvis-Patrick clustering", whatever that means.

Probably more relevent was this thread[2] on -hackers a while back with
pseudo-code[3]. How well it works, I don't know, it worked for him
evidently, he went away happy...

[1] http://archives.postgresql.org/pgsql-general/2005-11/msg00473.php
[2] http://archives.postgresql.org/pgsql-hackers/2005-11/msg01067.php
[3] http://archives.postgresql.org/pgsql-hackers/2005-11/msg01069.php

Hope this helps,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From pgsql-performance-owner@postgresql.org  Fri Jan 20 18:46:46 2006
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	pgsql-performance@postgreSQL.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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At 04:37 PM 1/20/2006, Martijn van Oosterhout wrote:
>On Fri, Jan 20, 2006 at 04:19:15PM -0500, Tom Lane wrote:
> >   %   cumulative   self              self     total
> >  time   seconds   seconds    calls  Ks/call  Ks/call  name
> >  98.96   1495.93  1495.93 33035195     0.00     0.00  hemdistsign
>
><snip>
>
> > So we gotta fix hemdistsign ...
>
>lol! Yeah, I guess so. Pretty nasty loop. LOOPBIT will iterate 8*63=504
>times and it's going to do silly bit handling on each and every
>iteration.
>
>Given that all it's doing is counting bits, a simple fix would be to
>loop over bytes, use XOR and count ones. For extreme speedup create a
>lookup table with 256 entries to give you the answer straight away...
For an even more extreme speedup, don't most modern CPUs have an asm 
instruction that counts the bits (un)set (AKA "population counting") 
in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b 
CPUs with SWAR instructions)?

Ron 



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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 05:46:34PM -0500, Ron wrote:
> For an even more extreme speedup, don't most modern CPUs have an asm 
> instruction that counts the bits (un)set (AKA "population counting") 
> in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b 
> CPUs with SWAR instructions)?

None in the x86 series that I'm aware of, at least.

You have instructions for finding the highest set bit, though.

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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Comments: In-reply-to Ron <rjpeace@earthlink.net>
	message dated "Fri, 20 Jan 2006 17:46:34 -0500"
Date: Fri, 20 Jan 2006 17:50:36 -0500
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Ron <rjpeace@earthlink.net> writes:
> For an even more extreme speedup, don't most modern CPUs have an asm 
> instruction that counts the bits (un)set (AKA "population counting") 
> in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b 
> CPUs with SWAR instructions)?

Yeah, but fetching from a small constant table is pretty quick too;
I doubt it's worth getting involved in machine-specific assembly code
for this.  I'm much more interested in the idea of improving the
furthest-distance algorithm in gtsvector_picksplit --- if we can do
that, it'll probably drop the distance calculation down to the point
where it's not really worth the trouble to assembly-code it.

			regards, tom lane

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From: Martijn van Oosterhout <kleptog@svana.org>
To: Ron <rjpeace@earthlink.net>
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On Fri, Jan 20, 2006 at 05:46:34PM -0500, Ron wrote:
> At 04:37 PM 1/20/2006, Martijn van Oosterhout wrote:
> >Given that all it's doing is counting bits, a simple fix would be to
> >loop over bytes, use XOR and count ones. For extreme speedup create a
> >lookup table with 256 entries to give you the answer straight away...
> For an even more extreme speedup, don't most modern CPUs have an asm=20
> instruction that counts the bits (un)set (AKA "population counting")=20
> in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b=20
> CPUs with SWAR instructions)?

Quite possibly, though I wouldn't have the foggiest idea how to get the
C compiler to generate it.

Given that even a lookup table will get you pretty close to that with
plain C coding, I think that's quite enough for a function that really
is just a small part of a much larger system...

Better solution (as Tom points out): work out how to avoid calling it
so much in the first place... At the moment each call to
gtsvector_picksplit seems to call the distance function around 14262
times. Getting that down by an order of magnitude will help much much
more.

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 05:50:36PM -0500, Tom Lane wrote:
> Yeah, but fetching from a small constant table is pretty quick too;
> I doubt it's worth getting involved in machine-specific assembly code
> for this.  I'm much more interested in the idea of improving the
> furthest-distance algorithm in gtsvector_picksplit --- if we can do
> that, it'll probably drop the distance calculation down to the point
> where it's not really worth the trouble to assembly-code it.

For the record: Could we do with a less-than-optimal split here? In that
case, an extremely simple heuristic is:

  best = distance(0, 1)
  best_i = 0
  best_j = 1

  for i = 2..last:
      if distance(best_i, i) > best:
          best = distance(best_i, i)
	  best_j = i
      else if distance(best_j, i) > best:
          best = distance(best_j, i)
	  best_i = i

I've tested it on various data, and although it's definitely not _correct_,
it generally gets within 10%.

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 05:29:46PM -0500, Ron wrote:
> If the N-dimensional space is Euclidean (any <x, x+1> is the same 
> distance apart in dimension x), then finding the farthest pair can be 
> done in at least O(n).

That sounds a bit optimistic.

  http://portal.acm.org/ft_gateway.cfm?id=167217&type=pdf&coll=GUIDE&dl=GUIDE&CFID=66230761&CFTOKEN=72453878

is from 1993, but still it struggles with getting it down to O(n log n)
deterministically, for Euclidian 3-space, and our problem is not Euclidian
(although it still satisfies the triangle inequality, which sounds important
to me) and in a significantly higher dimension...

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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Subject: Re: Creation of tsearch2 index is very slow 
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	message dated "Fri, 20 Jan 2006 17:49:53 +0100"
Date: Fri, 20 Jan 2006 18:22:39 -0500
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Stephan Vollmer <svollmer@gmx.de> writes:
> Tom Lane wrote:
>> However, I'm not sure that anyone's tried to do any performance
>> optimization on the GIST insert code ... there might be some low-hanging
>> fruit there.

> Unfortunately, I'm not able to investigate it further myself as I'm
> quite a Postgres newbie. But I could provide someone else with the
> example table. Maybe someone else could find out why it is so slow.

The problem seems to be mostly tsearch2's fault rather than the general
GIST code.  I've applied a partial fix to 8.1 and HEAD branches, which
you can find here if you're in a hurry for it:
http://archives.postgresql.org/pgsql-committers/2006-01/msg00283.php
(the gistidx.c change is all you need for tsearch2)

There is some followup discussion in the pgsql-performance list.  It
seems possible that we can get another factor of 10 or better with a
smarter picksplit algorithm --- but that patch will probably be too
large to be considered for back-patching into the stable branches.

			regards, tom lane

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To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> I wonder if there is a way to improve on that.

http://www.cs.uwaterloo.ca/~tmchan/slide_isaac.ps:

  The diameter problem has been studied extensively in the traditional model.
  Although O(n log n) algorithms have been given for d = 2 and d = 3, only
  slightly subquadratic algorithms are known for higher dimensions.

It doesn't mention a date, but has references to at least 2004-papers, so I'm
fairly sure nothing big has happened since that.

It sounds like we either want to go for an approximation, or just accept that
it's a lot of work to get it better than O(n^2). Or, of course, find some
special property of our problem that makes it easier than the general problem
:-)

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 19:52:41 2006
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"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
> For the record: Could we do with a less-than-optimal split here?

Yeah, I was wondering the same.  The code is basically choosing two
"seed" values to drive the index-page split.  Intuitively it seems that
"pretty far apart" would be nearly as good as "absolute furthest apart"
for this purpose.

The cost of a less-than-optimal split would be paid on all subsequent
index accesses, though, so it's not clear how far we can afford to go in
this direction.

It's also worth considering that the entire approach is a heuristic,
really --- getting the furthest-apart pair of seeds doesn't guarantee
an optimal split as far as I can see.  Maybe there's some totally
different way to do it.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Fri Jan 20 20:05:17 2006
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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
> It's also worth considering that the entire approach is a heuristic,
> really --- getting the furthest-apart pair of seeds doesn't guarantee
> an optimal split as far as I can see.  Maybe there's some totally
> different way to do it.

For those of us who don't know what tsearch2/gist is trying to accomplish
here, could you provide some pointers? :-) During my mini-literature-search
on Google, I've found various algorithms for locating clusters in
high-dimensional metric spaces[1]; some of it might be useful, but I might
just be misunderstanding what the real problem is.

[1] http://ieeexplore.ieee.org/iel5/69/30435/01401892.pdf?arnumber=1401892 ,
    for instance

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 20:23:11 2006
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"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
> On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
>> It's also worth considering that the entire approach is a heuristic,
>> really --- getting the furthest-apart pair of seeds doesn't guarantee
>> an optimal split as far as I can see.  Maybe there's some totally
>> different way to do it.

> For those of us who don't know what tsearch2/gist is trying to accomplish
> here, could you provide some pointers? :-)

Well, we're trying to split an index page that's gotten full into two
index pages, preferably with approximately equal numbers of items in
each new page (this isn't a hard requirement though).  I think the true
figure of merit for a split is how often will subsequent searches have
to descend into *both* of the resulting pages as opposed to just one
--- the less often that is true, the better.  I'm not very clear on
what tsearch2 is doing with these bitmaps, but it looks like an upper
page's downlink has the union (bitwise OR) of the one-bits in the values
on the lower page, and you have to visit the lower page if this union
has a nonempty intersection with the set you are looking for.  If that's
correct, what you really want is to divide the values so that the unions
of the two sets have minimal overlap ... which seems to me to have
little to do with what the code does at present.

Teodor, Oleg, can you clarify what's needed here?

			regards, tom lane

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From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org, Teodor Sigaev <teodor@sigaev.ru>,
	Oleg Bartunov <oleg@sai.msu.su>
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Fri, Jan 20, 2006 at 07:23:10PM -0500, Tom Lane wrote:
> I'm not very clear on what tsearch2 is doing with these bitmaps, but it
> looks like an upper page's downlink has the union (bitwise OR) of the
> one-bits in the values on the lower page, and you have to visit the lower
> page if this union has a nonempty intersection with the set you are looking
> for.  If that's correct, what you really want is to divide the values so
> that the unions of the two sets have minimal overlap ... which seems to me
> to have little to do with what the code does at present.

Sort of like the vertex-cover problem? That's probably a lot harder than
finding the two farthest points...

/* Steinar */
-- 
Homepage: http://www.sesse.net/

From pgsql-performance-owner@postgresql.org  Fri Jan 20 21:34:52 2006
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	Oleg Bartunov <oleg@sai.msu.su>
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
References: <26153.1137784469@sss.pgh.pa.us>
 <20060120201036.GE31908@svana.org>
	<26583.1137788505@sss.pgh.pa.us> <20060120205132.GF31908@svana.org>
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Tom Lane wrote:
> Well, we're trying to split an index page that's gotten full into two
> index pages, preferably with approximately equal numbers of items in
> each new page (this isn't a hard requirement though).  ...  If that's
> correct, what you really want is to divide the values so that the unions
> of the two sets have minimal overlap ... which seems to me to have
> little to do with what the code does at present.

This problem has been studied extensively by chemists, and they haven't found any easy solutions.

The Jarvis Patrick clustering algorithm might give you hints about a fast approach.  In theory it's K*O(N^2), but J-P is preferred for large datasets (millions of molecules) because the coefficient K can be made quite low.  It starts with a "similarity metric" for two bit strings, the Tanimoto or Tversky coefficients:

  http://www.daylight.com/dayhtml/doc/theory/theory.finger.html#RTFToC83

J-P Clustering is described here:

  http://www.daylight.com/dayhtml/doc/cluster/cluster.a.html#cl33

J-P Clustering is probably not the best for this problem (see the illustrations in the link above to see why), but the general idea of computing N-nearest-neighbors, followed by a partitioning step, could be what's needed.

Craig

From pgsql-performance-owner@postgresql.org  Sat Jan 21 04:00:21 2006
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From: Rikard Pavelic <rikard.pavelic@zg.htnet.hr>
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To: "Jim C. Nasby" <jnasby@pervasive.com>
CC: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Stored Procedures
References: <43D130EF.3010205@zg.htnet.hr>
	<20060120191031.GO20182@pervasive.com>
	<43D13C2F.1030203@zg.htnet.hr>
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Jim C. Nasby wrote:
> If you're dealing with something that's performance critical you're not
> going to be constantly re-connecting anyway, so I don't see what the
> issue is.
>   

I really missed your point.
In multi user environment where each user uses it's connection for 
identification
purposes, this seems like a reasonable optimization.

I know there is pgpool, but it's non windows, and it's not the best 
solution
for every other problem.


From pgsql-performance-owner@postgresql.org  Sat Jan 21 08:22:50 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>,pgsql-performance@postgresql.org,
From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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At 07:23 PM 1/20/2006, Tom Lane wrote:
>"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
> > On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
> >> It's also worth considering that the entire approach is a heuristic,
> >> really --- getting the furthest-apart pair of seeds doesn't guarantee
> >> an optimal split as far as I can see.  Maybe there's some totally
> >> different way to do it.
>
> > For those of us who don't know what tsearch2/gist is trying to accomplish
> > here, could you provide some pointers? :-)
>
>Well, we're trying to split an index page that's gotten full into 
>two index pages, preferably with approximately equal numbers of items in
>each new page (this isn't a hard requirement though).

Maybe we are over thinking this.  What happens if we do the obvious 
and just make a new page and move the "last" n/2 items on the full 
page to the new page?

Various forms of "move the last n/2 items" can be tested here:
0= just split the table in half.  Sometimes KISS  works. O(1).
1= the one's with the highest (or lowest) "x" value.
2= the one's with the highest sum of coordinates (x+y+...= values in 
the top/bottom n/2 of entries).
3= split the table so that each table has entries whose size_waste 
values add up to approximately the same value.
4= I'm sure there are others.
1-5 can be done in O(n) time w/o auxiliary data.  They can be done in 
O(1) if we've kept track of the appropriate metric as we've built the 
current page.


>I think the true figure of merit for a split is how often will 
>subsequent searches have to descend into *both* of the resulting 
>pages as opposed to just one
>--- the less often that is true, the better.  I'm not very clear on 
>what tsearch2 is doing with these bitmaps, but it looks like an 
>upper page's downlink has the union (bitwise OR) of the one-bits in 
>the values on the lower page, and you have to visit the lower page 
>if this union has a nonempty intersection with the set you are 
>looking for.  If that's correct, what you really want is to divide 
>the values so that the unions of the two sets have minimal overlap 
>... which seems to me to have little to do with what the code does at present.
I'm not sure what "upper page" and "lower page" mean here?


>Teodor, Oleg, can you clarify what's needed here?
Ditto.  Guys what is the real motivation and purpose for this code?

Ron 



From pgsql-performance-owner@postgresql.org  Sat Jan 21 09:08:40 2006
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From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Ron <rjpeace@earthlink.net>, pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Message-ID: <20060121130830.GA9955@svana.org>
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 <20060120170452.GC31908@svana.org>
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On Fri, Jan 20, 2006 at 05:50:36PM -0500, Tom Lane wrote:
> Yeah, but fetching from a small constant table is pretty quick too;
> I doubt it's worth getting involved in machine-specific assembly code
> for this.  I'm much more interested in the idea of improving the
> furthest-distance algorithm in gtsvector_picksplit --- if we can do
> that, it'll probably drop the distance calculation down to the point
> where it's not really worth the trouble to assembly-code it.

I've played with another algorithm. Very simple but it's only O(N). It
doesn't get the longest distance but it does get close. Basically you
take the first two elements as your starting length. Then you loop over
each remaining string, each time finding the longest pair out of each
set of three.

I've only tried it on random strings. The maximum distance for 128
random strings tends to be around 291-295. This algorithm tends to find
lengths around 280. Pseudo code below (in Perl).

However, IMHO, this algorithm is optimising the wrong thing. It
shouldn't be trying to split into sets that are far apart, it should be
trying to split into sets that minimize the number of set bits (ie
distance from zero), since that's what's will speed up searching.
That's harder though (this algorithm does approximate it sort of)
and I havn't come up with an algorithm yet

sub MaxDistFast
{
  my $strings =3D shift;
=20
  my $m1 =3D 0;
  my $m2 =3D 1;
  my $dist =3D -1;

  for my $i (2..$#$strings)
  {
    my $d1 =3D HammDist( $strings->[$i], $strings->[$m1] );
    my $d2 =3D HammDist( $strings->[$i], $strings->[$m2] );

    my $m =3D ($d1 > $d2) ? $m1 : $m2;
    my $d =3D ($d1 > $d2) ? $d1 : $d2;
   =20
    if( $d > $dist )
    {
      $dist =3D $d;
      $m1 =3D $i; =20
      $m2 =3D $m;
    }
  }
  return($m1,$m2,$dist);
}

Full program available at:
http://svana.org/kleptog/temp/picksplit.pl

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From: K C Lau <kclau60@netvigator.com>
Subject: Re: SELECT MIN, MAX took longer time than SELECT
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At 01:20 06/01/21, Jim C. Nasby wrote:

>BTW, these queries below are meaningless; they are not equivalent to
>min(logsn).
>
> > esdt=> explain analyze select LogSN from Log where create_time <
> > '2005/10/19' order by create_time limit 1;

Thank you for pointing it out.

It actually returns the min(logsn), as the index is on (create_time, 
logsn). To be more explicit, I have changed to query to:
explain analyze select LogSN from Log where create_time < '2005/10/19' 
order by create_time, logsn limit 1;

esdt=> \d log;
  create_time | character varying(23)   | default 
'1970/01/01~00:00:00.000'::character varying
  logsn       | integer                 | not null
  ...
Indexes:
     "pk_log" PRIMARY KEY, btree (logsn)
     "idx_logtime" btree (create_time, logsn)

Best regards,
KC.


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On Sat, 21 Jan 2006, Martijn van Oosterhout wrote:

> However, IMHO, this algorithm is optimising the wrong thing. It
> shouldn't be trying to split into sets that are far apart, it should be
> trying to split into sets that minimize the number of set bits (ie
> distance from zero), since that's what's will speed up searching.

Martijn, you're right! We want not only to split page to very
different parts, but not to increase the number of sets bits in
resulted signatures, which are union (OR'ed) of all signatures 
in part. We need not only fast index creation (thanks, Tom !),
but a better index. Some information is available here
http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
There are should be more detailed document, but I don't remember where:)

> That's harder though (this algorithm does approximate it sort of)
> and I havn't come up with an algorithm yet

Don't ask how hard we thought :)

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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On Sat, 21 Jan 2006, Ron wrote:

> At 07:23 PM 1/20/2006, Tom Lane wrote:
>> "Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
>> > On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
>> >> It's also worth considering that the entire approach is a heuristic,
>> >> really --- getting the furthest-apart pair of seeds doesn't guarantee
>> >> an optimal split as far as I can see.  Maybe there's some totally
>> >> different way to do it.
>> 
>> > For those of us who don't know what tsearch2/gist is trying to accomplish
>> > here, could you provide some pointers? :-)
>> 
>> Well, we're trying to split an index page that's gotten full into two index 
>> pages, preferably with approximately equal numbers of items in
>> each new page (this isn't a hard requirement though).
>
> Maybe we are over thinking this.  What happens if we do the obvious and just 
> make a new page and move the "last" n/2 items on the full page to the new 
> page?
>
> Various forms of "move the last n/2 items" can be tested here:
> 0= just split the table in half.  Sometimes KISS  works. O(1).
> 1= the one's with the highest (or lowest) "x" value.
> 2= the one's with the highest sum of coordinates (x+y+...= values in the 
> top/bottom n/2 of entries).
> 3= split the table so that each table has entries whose size_waste values add 
> up to approximately the same value.
> 4= I'm sure there are others.
> 1-5 can be done in O(n) time w/o auxiliary data.  They can be done in O(1) if 
> we've kept track of the appropriate metric as we've built the current page.
>
>
>> I think the true figure of merit for a split is how often will subsequent 
>> searches have to descend into *both* of the resulting pages as opposed to 
>> just one
>> --- the less often that is true, the better.  I'm not very clear on what 
>> tsearch2 is doing with these bitmaps, but it looks like an upper page's 
>> downlink has the union (bitwise OR) of the one-bits in the values on the 
>> lower page, and you have to visit the lower page if this union has a 
>> nonempty intersection with the set you are looking for.  If that's correct, 
>> what you really want is to divide the values so that the unions of the two 
>> sets have minimal overlap ... which seems to me to have little to do with 
>> what the code does at present.
> I'm not sure what "upper page" and "lower page" mean here?
>
>
>> Teodor, Oleg, can you clarify what's needed here?
> Ditto.  Guys what is the real motivation and purpose for this code?

we want not just split the page by two very distinct parts, but to keep
resulted signatures which is ORed signature of all signatures in the page
as much 'sparse' as can. 
some information available here
http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals

Unfortunately, we're rather busy right now and couldn't be very useful.

>
> Ron 
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

From pgsql-performance-owner@postgresql.org  Sat Jan 21 09:39:13 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
From: K C Lau <kclau60@netvigator.com>
Subject: Re: SELECT MIN, MAX took longer time than SELECT
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I have worked round the issue by using 2 separate queries with the LIMIT 
construct.

LogSN and create_time are indeed directly correlated, both monotonously 
increasing, occasionally with multiple LogSN's having the same create_time.

What puzzles me is why the query with COUNT, MIN, MAX uses idx_logtime for 
the scan, but the query without the COUNT uses pk_log and takes much 
longer. If it had chosen idx_logtime instead, then it should have returned 
immediately for both MIN and MAX.

Best regards,
KC.

At 02:51 06/01/21, Tom Lane wrote:
>"Jim C. Nasby" <jnasby@pervasive.com> writes:
> > On Fri, Jan 20, 2006 at 12:35:36PM +0800, K C Lau wrote:
> > Here's the problem... the estimate for the backwards index scan is *way*
> > off:
>
> >> ->  Limit  (cost=0.00..1.26 rows=1 width=4) (actual
> >> time=200032.928..200032.931 rows=1 loops=1)
> >> ->  Index Scan Backward using pk_log on
> >> log  (cost=0.00..108047.11 rows=86089 width=4) (actual
> >> time=200032.920..200032.920 rows=1 loops=1)
> >> Filter: (((create_time)::text < '2005/10/19'::text) AND
> >> (logsn IS NOT NULL))
> >> Total runtime: 200051.701 ms
>
>It's more subtle than you think.  The estimated rowcount is the
>estimated number of rows fetched if the indexscan were run to
>completion, which it isn't because the LIMIT cuts it off after the
>first returned row.  That estimate is not bad (we can see from the
>aggregate plan that the true value would have been 106708, assuming
>that the "logsn IS NOT NULL" condition isn't filtering anything).
>
>The real problem is that it's taking quite a long time for the scan
>to reach the first row with create_time < 2005/10/19, which is not
>too surprising if logsn is strongly correlated with create_time ...
>but in the absence of any cross-column statistics the planner has
>no very good way to know that.  (Hm ... but both of them probably
>also show a strong correlation to physical order ... we could look
>at that maybe ...)  The default assumption is that the two columns
>aren't correlated and so it should not take long to hit the first such
>row, which is why the planner likes the indexscan/limit plan.
>
>                         regards, tom lane


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On Sat, Jan 21, 2006 at 04:29:13PM +0300, Oleg Bartunov wrote:
> Martijn, you're right! We want not only to split page to very
> different parts, but not to increase the number of sets bits in
> resulted signatures, which are union (OR'ed) of all signatures=20
> in part. We need not only fast index creation (thanks, Tom !),
> but a better index. Some information is available here
> http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
> There are should be more detailed document, but I don't remember where:)

I see how it works, what I don't quite get is whether the "inverted
index" you refer to is what we're working with here, or just what's in
tsearchd?

> >That's harder though (this algorithm does approximate it sort of)
> >and I havn't come up with an algorithm yet
>=20
> Don't ask how hard we thought :)

Well, looking at how other people are struggling with it, it's
definitly a Hard Problem. One thing though, I don't think the picksplit
algorithm as is really requires you to strictly have the longest
distance, just something reasonably long. So I think the alternate
algorithm I posted should produce equivalent results. No idea how to
test it though...

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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	pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
In-Reply-To: <20060121150424.GB9955@svana.org>
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On Sat, 21 Jan 2006, Martijn van Oosterhout wrote:

> On Sat, Jan 21, 2006 at 04:29:13PM +0300, Oleg Bartunov wrote:
>> Martijn, you're right! We want not only to split page to very
>> different parts, but not to increase the number of sets bits in
>> resulted signatures, which are union (OR'ed) of all signatures
>> in part. We need not only fast index creation (thanks, Tom !),
>> but a better index. Some information is available here
>> http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
>> There are should be more detailed document, but I don't remember where:)
>
> I see how it works, what I don't quite get is whether the "inverted
> index" you refer to is what we're working with here, or just what's in
> tsearchd?

just tsearchd. We plan to implement inverted index into PostgreSQL core
and then adapt tsearch2 to use it as option for read-only archives.

>
>>> That's harder though (this algorithm does approximate it sort of)
>>> and I havn't come up with an algorithm yet
>>
>> Don't ask how hard we thought :)
>
> Well, looking at how other people are struggling with it, it's
> definitly a Hard Problem. One thing though, I don't think the picksplit
> algorithm as is really requires you to strictly have the longest
> distance, just something reasonably long. So I think the alternate
> algorithm I posted should produce equivalent results. No idea how to
> test it though...

you may try our development module 'gevel' to see how dense is a signature.

www=# \d v_pages
           Table "public.v_pages"
   Column   |       Type        | Modifiers
-----------+-------------------+-----------
  tid       | integer           | not null
  path      | character varying | not null
  body      | character varying |
  title     | character varying |
  di        | integer           |
  dlm       | integer           |
  de        | integer           |
  md5       | character(22)     |
  fts_index | tsvector          |
Indexes:
     "v_pages_pkey" PRIMARY KEY, btree (tid)
     "v_pages_path_key" UNIQUE, btree (path)
     "v_gist_key" gist (fts_index)

# select * from gist_print('v_gist_key') as t(level int, valid bool, a gtsvector) where level =1;
  level | valid |               a
-------+-------+--------------------------------
      1 | t     | 1698 true bits, 318 false bits
      1 | t     | 1699 true bits, 317 false bits
      1 | t     | 1701 true bits, 315 false bits
      1 | t     | 1500 true bits, 516 false bits
      1 | t     | 1517 true bits, 499 false bits
(5 rows)



 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

From pgsql-performance-owner@postgresql.org  Sat Jan 21 13:29:39 2006
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From: Oleg Bartunov <oleg@sai.msu.su>
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To: Martijn van Oosterhout <kleptog@svana.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Ron <rjpeace@earthlink.net>,
	pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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gevel is available from 
http://www.sai.msu.su/~megera/postgres/gist/

 	Oleg
On Sat, 21 Jan 2006, Martijn van Oosterhout wrote:

> On Sat, Jan 21, 2006 at 04:29:13PM +0300, Oleg Bartunov wrote:
>> Martijn, you're right! We want not only to split page to very
>> different parts, but not to increase the number of sets bits in
>> resulted signatures, which are union (OR'ed) of all signatures
>> in part. We need not only fast index creation (thanks, Tom !),
>> but a better index. Some information is available here
>> http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
>> There are should be more detailed document, but I don't remember where:)
>
> I see how it works, what I don't quite get is whether the "inverted
> index" you refer to is what we're working with here, or just what's in
> tsearchd?
>
>>> That's harder though (this algorithm does approximate it sort of)
>>> and I havn't come up with an algorithm yet
>>
>> Don't ask how hard we thought :)
>
> Well, looking at how other people are struggling with it, it's
> definitly a Hard Problem. One thing though, I don't think the picksplit
> algorithm as is really requires you to strictly have the longest
> distance, just something reasonably long. So I think the alternate
> algorithm I posted should produce equivalent results. No idea how to
> test it though...
>
> Have a nice day,
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

From pgsql-performance-owner@postgresql.org  Sat Jan 21 12:39:42 2006
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To: Oleg Bartunov <oleg@sai.msu.su>, pgsql-performance@postgresql.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
Cc: Tom Lane <tgl@sss.pgh.pa.us>
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Perhaps a different approach to this problem is called for:

_Managing Gigabytes: Compressing and Indexing Documents and Images_  2ed
Witten, Moffat, Bell
ISBN 1-55860-570-3

This is a VERY good book on the subject.

I'd also suggest looking at the publicly available work on indexing 
and searching for search engines like Inktomi (sp?) and Google.
Ron


At 08:34 AM 1/21/2006, Oleg Bartunov wrote:
>On Sat, 21 Jan 2006, Ron wrote:
>
>>At 07:23 PM 1/20/2006, Tom Lane wrote:
>>>"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
>>> > On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
>>> >> It's also worth considering that the entire approach is a heuristic,
>>> >> really --- getting the furthest-apart pair of seeds doesn't guarantee
>>> >> an optimal split as far as I can see.  Maybe there's some totally
>>> >> different way to do it.
>>> > For those of us who don't know what tsearch2/gist is trying to accomplish
>>> > here, could you provide some pointers? :-)
>>>Well, we're trying to split an index page that's gotten full into 
>>>two index pages, preferably with approximately equal numbers of items in
>>>each new page (this isn't a hard requirement though).
>>
>>Maybe we are over thinking this.  What happens if we do the obvious 
>>and just make a new page and move the "last" n/2 items on the full 
>>page to the new page?
>>
>>Various forms of "move the last n/2 items" can be tested here:
>>0= just split the table in half.  Sometimes KISS  works. O(1).
>>1= the one's with the highest (or lowest) "x" value.
>>2= the one's with the highest sum of coordinates (x+y+...= values 
>>in the top/bottom n/2 of entries).
>>3= split the table so that each table has entries whose size_waste 
>>values add up to approximately the same value.
>>4= I'm sure there are others.
>>1-5 can be done in O(n) time w/o auxiliary data.  They can be done 
>>in O(1) if we've kept track of the appropriate metric as we've 
>>built the current page.
>>
>>
>>>I think the true figure of merit for a split is how often will 
>>>subsequent searches have to descend into *both* of the resulting 
>>>pages as opposed to just one
>>>--- the less often that is true, the better.  I'm not very clear 
>>>on what tsearch2 is doing with these bitmaps, but it looks like an 
>>>upper page's downlink has the union (bitwise OR) of the one-bits 
>>>in the values on the lower page, and you have to visit the lower 
>>>page if this union has a nonempty intersection with the set you 
>>>are looking for.  If that's correct, what you really want is to 
>>>divide the values so that the unions of the two sets have minimal 
>>>overlap ... which seems to me to have little to do with what the 
>>>code does at present.
>>I'm not sure what "upper page" and "lower page" mean here?
>>
>>
>>>Teodor, Oleg, can you clarify what's needed here?
>>Ditto.  Guys what is the real motivation and purpose for this code?
>
>we want not just split the page by two very distinct parts, but to keep
>resulted signatures which is ORed signature of all signatures in the page
>as much 'sparse' as can. some information available here
>http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
>
>Unfortunately, we're rather busy right now and couldn't be very useful.



From pgsql-performance-owner@postgresql.org  Sat Jan 21 12:33:40 2006
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Date: Sat, 21 Jan 2006 19:33:27 +0300 (MSK)
From: Oleg Bartunov <oleg@sai.msu.su>
X-X-Sender: megera@ra.sai.msu.su
To: Ron <rjpeace@earthlink.net>
cc: pgsql-performance@postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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On Sat, 21 Jan 2006, Ron wrote:

> Perhaps a different approach to this problem is called for:
>
> _Managing Gigabytes: Compressing and Indexing Documents and Images_  2ed
> Witten, Moffat, Bell
> ISBN 1-55860-570-3
>
> This is a VERY good book on the subject.
>
> I'd also suggest looking at the publicly available work on indexing and 
> searching for search engines like Inktomi (sp?) and Google.
> Ron

Ron,

you completely miss the problem ! We do know MG and other SE.  Actually,
we've implemented several search engines based on inverted index technology 
(see, for example, pgsql.ru/db/pgsearch). tsearch2 was designed for
online indexing, while keeping inverted index online is rather difficult
problem. We do have plan to implement inverted index as an option for
large read-only archives, but now we discuss how to organize online
index and if possible to optimize current storage for signatures 
without breaking search performance.

>
>
> At 08:34 AM 1/21/2006, Oleg Bartunov wrote:
>> On Sat, 21 Jan 2006, Ron wrote:
>> 
>>> At 07:23 PM 1/20/2006, Tom Lane wrote:
>>>> "Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
>>>> > On Fri, Jan 20, 2006 at 06:52:37PM -0500, Tom Lane wrote:
>>>> >> It's also worth considering that the entire approach is a heuristic,
>>>> >> really --- getting the furthest-apart pair of seeds doesn't guarantee
>>>> >> an optimal split as far as I can see.  Maybe there's some totally
>>>> >> different way to do it.
>>>> > For those of us who don't know what tsearch2/gist is trying to 
>>>> accomplish
>>>> > here, could you provide some pointers? :-)
>>>> Well, we're trying to split an index page that's gotten full into two 
>>>> index pages, preferably with approximately equal numbers of items in
>>>> each new page (this isn't a hard requirement though).
>>> 
>>> Maybe we are over thinking this.  What happens if we do the obvious and 
>>> just make a new page and move the "last" n/2 items on the full page to the 
>>> new page?
>>> 
>>> Various forms of "move the last n/2 items" can be tested here:
>>> 0= just split the table in half.  Sometimes KISS  works. O(1).
>>> 1= the one's with the highest (or lowest) "x" value.
>>> 2= the one's with the highest sum of coordinates (x+y+...= values in the 
>>> top/bottom n/2 of entries).
>>> 3= split the table so that each table has entries whose size_waste values 
>>> add up to approximately the same value.
>>> 4= I'm sure there are others.
>>> 1-5 can be done in O(n) time w/o auxiliary data.  They can be done in O(1) 
>>> if we've kept track of the appropriate metric as we've built the current 
>>> page.
>>> 
>>> 
>>>> I think the true figure of merit for a split is how often will subsequent 
>>>> searches have to descend into *both* of the resulting pages as opposed to 
>>>> just one
>>>> --- the less often that is true, the better.  I'm not very clear on what 
>>>> tsearch2 is doing with these bitmaps, but it looks like an upper page's 
>>>> downlink has the union (bitwise OR) of the one-bits in the values on the 
>>>> lower page, and you have to visit the lower page if this union has a 
>>>> nonempty intersection with the set you are looking for.  If that's 
>>>> correct, what you really want is to divide the values so that the unions 
>>>> of the two sets have minimal overlap ... which seems to me to have little 
>>>> to do with what the code does at present.
>>> I'm not sure what "upper page" and "lower page" mean here?
>>> 
>>> 
>>>> Teodor, Oleg, can you clarify what's needed here?
>>> Ditto.  Guys what is the real motivation and purpose for this code?
>> 
>> we want not just split the page by two very distinct parts, but to keep
>> resulted signatures which is ORed signature of all signatures in the page
>> as much 'sparse' as can. some information available here
>> http://www.sai.msu.su/~megera/oddmuse/index.cgi/Tsearch_V2_internals
>> 
>> Unfortunately, we're rather busy right now and couldn't be very useful.
>
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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To: Ron <rjpeace@earthlink.net>
cc: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very 
In-reply-to: <7.0.1.0.2.20060121064930.03aba810@earthlink.net> 
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Comments: In-reply-to Ron <rjpeace@earthlink.net>
	message dated "Sat, 21 Jan 2006 07:22:32 -0500"
Date: Sat, 21 Jan 2006 13:27:53 -0500
Message-ID: <18771.1137868073@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Ron <rjpeace@earthlink.net> writes:
> At 07:23 PM 1/20/2006, Tom Lane wrote:
>> Well, we're trying to split an index page that's gotten full into 
>> two index pages, preferably with approximately equal numbers of items in
>> each new page (this isn't a hard requirement though).

> Maybe we are over thinking this.  What happens if we do the obvious 
> and just make a new page and move the "last" n/2 items on the full 
> page to the new page?

Search performance will go to hell in a handbasket :-(.  We have to make
at least some effort to split the page in a way that will allow searches
to visit only one of the two child pages rather than both.

It's certainly true though that finding the furthest pair is not a
necessary component of that.  It's reasonable if you try to visualize
the problem in 2D or 3D, but I'm not sure that that geometric intuition
holds up in such a high-dimensional space as we have here.

			regards, tom lane

From pgsql-general-owner@postgresql.org  Sat Jan 21 14:37:24 2006
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To: pgsql-general@postgresql.org
Subject: Re: Creation of tsearch2 index is very slow
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Tom Lane wrote:

> The problem seems to be mostly tsearch2's fault rather than the general=

> GIST code.  I've applied a partial fix to 8.1 and HEAD branches, which
> you can find here if you're in a hurry for it:
> http://archives.postgresql.org/pgsql-committers/2006-01/msg00283.php
> (the gistidx.c change is all you need for tsearch2)

Thanks for all your time and work you and the other guys are
spending on this matter! I'll look into the new version, but a.p.o
seems to be unreachable at the moment.


> There is some followup discussion in the pgsql-performance list.  It
> seems possible that we can get another factor of 10 or better with a
> smarter picksplit algorithm --- but that patch will probably be too
> large to be considered for back-patching into the stable branches.

I've already been following the discussion on pgsql-perform,
although I have to admit that don't understand every detail of the
tsearch2 implementation. :-)  Thus, I'm sorry that I won't be able
to help directly on that problem. But it is interesting to read anyway.

Best regards,

- Stephan


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From pgsql-performance-owner@postgresql.org  Sat Jan 21 16:48:10 2006
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Ron <rjpeace@earthlink.net>, pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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On Sat, 21 Jan 2006, Tom Lane wrote:

> Ron <rjpeace@earthlink.net> writes:
>> At 07:23 PM 1/20/2006, Tom Lane wrote:
>>> Well, we're trying to split an index page that's gotten full into
>>> two index pages, preferably with approximately equal numbers of items in
>>> each new page (this isn't a hard requirement though).
>
>> Maybe we are over thinking this.  What happens if we do the obvious
>> and just make a new page and move the "last" n/2 items on the full
>> page to the new page?
>
> Search performance will go to hell in a handbasket :-(.  We have to make
> at least some effort to split the page in a way that will allow searches
> to visit only one of the two child pages rather than both.

does the order of the items within a given page matter? if not this sounds 
like a partial quicksort algorithm would work. you don't need to fully 
sort things, but you do want to make sure that everything on the first 
page is 'less' then everything on the second page so you can skip passes 
that don't cross a page boundry

> It's certainly true though that finding the furthest pair is not a
> necessary component of that.  It's reasonable if you try to visualize
> the problem in 2D or 3D, but I'm not sure that that geometric intuition
> holds up in such a high-dimensional space as we have here.

I will say that I'm not understanding the problem well enough to 
understand themulti-dimentional nature of this problem.

David Lang

From pgsql-performance-owner@postgresql.org  Sat Jan 21 16:36:36 2006
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From: Martijn van Oosterhout <kleptog@svana.org>
To: Oleg Bartunov <oleg@sai.msu.su>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Ron <rjpeace@earthlink.net>,
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Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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On Sat, Jan 21, 2006 at 06:22:52PM +0300, Oleg Bartunov wrote:
> >I see how it works, what I don't quite get is whether the "inverted
> >index" you refer to is what we're working with here, or just what's in
> >tsearchd?
>=20
> just tsearchd. We plan to implement inverted index into PostgreSQL core
> and then adapt tsearch2 to use it as option for read-only archives.

Hmm, had a look and think about it and I think I see what you mean by
an inverted index. I also think your going to have a real exercise
implementing it in Postgres because postgres indexes work on the basis
of one tuple, one index entry, which I think your inverted index
doesn't do.

That said, I think GiST could be extended to support your case without
too much difficulty. Interesting project though :)

BTW, given you appear to have a tsearch2 index with some real-world
data, would you be willing to try some alternate picksplit algorithms
to see if your gevel module shows any difference?

Have a nice day,
--=20
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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From pgsql-performance-owner@postgresql.org  Sat Jan 21 16:55:24 2006
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From: =?ISO-8859-1?Q?=DCmit_=D6ztosun?= <umit@likyabilisim.com>
To: pgsql-performance@postgresql.org
Subject: Slow queries consisting inner selects and order bys & hack to speed
 up
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Hello,

Our application uses typical queries similar to following (very simplified)=
:

SELECT
 part_id,
 part_name,
 (SELECT
  SUM(amount) FROM part_movements M
  WHERE P.part_id =3D M.part_id
 ) as part_amount
FROM parts P
LIMIT 50

The parts table holds thousands of items. Movement table stores yearly
movement information of those items. We are presenting results to users pag=
e
by page, hence the limit case.

User can sort and filter results. When sorting is introduced, query
performance drops significantly:

SELECT
 part_id,
 part_name,
 (SELECT
  SUM(amount) FROM part_movements M
  WHERE P.part_id =3D M.part_id
 ) as part_amount
FROM parts P
ORDER BY part_name
LIMIT 50

Postgres seems to compute all possible rows and then sorts the
results, which nearly renders the paging meaningless. A dummy WHERE
case dramatically improves performance:

SELECT
 part_id,
 part_name,
 (SELECT
  SUM(amount) FROM part_movements M
  WHERE P.part_id =3D M.part_id
 ) as part_amount
FROM parts P
ORDER BY part_name
WHERE part_amount > -10000000
LIMIT 50

Is there a way to improve performance of these queries? Is it possible
to instruct Postgres to first sort the rows then compute the inner
queries? (We have simulated this by using temporary tables and two
stage queries, but this is not practical because most queries are
automatically generated).

Attached is the output of real queries and their corresponding EXPLAIN
ANALYZE outputs.

Regards,
Umit Oztosun

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From pgsql-performance-owner@postgresql.org  Sat Jan 21 16:56:30 2006
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To: David Lang <dlang@invendra.net>
cc: Ron <rjpeace@earthlink.net>, pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very 
In-reply-to: <Pine.LNX.4.62.0601211204300.4943@qnivq.ynat.uz> 
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Comments: In-reply-to David Lang <dlang@invendra.net>
	message dated "Sat, 21 Jan 2006 12:19:26 -0800"
Date: Sat, 21 Jan 2006 15:55:49 -0500
Message-ID: <1749.1137876949@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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David Lang <dlang@invendra.net> writes:
> On Sat, 21 Jan 2006, Tom Lane wrote:
>> Ron <rjpeace@earthlink.net> writes:
>>> Maybe we are over thinking this.  What happens if we do the obvious
>>> and just make a new page and move the "last" n/2 items on the full
>>> page to the new page?
>> 
>> Search performance will go to hell in a handbasket :-(.  We have to make
>> at least some effort to split the page in a way that will allow searches
>> to visit only one of the two child pages rather than both.

> does the order of the items within a given page matter?

AFAIK the items within a GIST index page are just stored in insertion
order (which is exactly why Ron's suggestion above doesn't work well).
There's no semantic significance to it.  It's only when we have to split
the page that we need to classify the items more finely.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 21 17:06:58 2006
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Subject: Re: [PERFORMANCE] Stored Procedures
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Jim C. Nasby wrote:
> If you're dealing with something that's performance critical you're not
> going to be constantly re-connecting anyway, so I don't see what the
> issue is.
>   

I didn't include mailing list in my second reply :( so here it is again.
Someone may find this interesting...

http://archives.postgresql.org/pgsql-general/2004-04/msg00084.php

 From Tom Lane:
"EXECUTE means something different in plpgsql than it does in plain SQL,

and you do not need PREPARE at all in plpgsql.  plpgsql's automatic
caching of plans gives you the effect of PREPARE on every statement
without your having to ask for it."


From pgsql-performance-owner@postgresql.org  Sat Jan 21 19:49:53 2006
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Subject: libpq vs. unixODBC performance
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From: "Constantine Filin" <cfilin@intermedia.net>
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Greetings -

I am really love Postgres and do enjoy hacking around it but I just
met a libpq performance issue that I would like to get your help with.

I have Postgres 8.0.1 running on Linux version 2.6.10-1.771_FC2.

I have an application that makes queries to Postgres. I want to keep
the database code in this application as simple as possible because
the application is doing lots of other complex things (it is an IP
Telephony server). So for the sake of simplicity, I do not "prepare"
SQL statements before submitting them to database.

Now I have 2 ways to access Postgres - one through unixODBC, the=20
other through libpq. I found that libpq performance is nearly 2 times
slower than performance of unixODBC. Specifically, I have a
multithreaded
test program (using pthreads), where I can run a specified number of
simple queries like this:

SELECT * FROM extensions WHERE=20
	(somecolumn IS NOT NULL)=20
	AND (id IN (SELECT extension_id FROM table 2))

The test program can submit the queries using unixODBC or libpq.=20

With 1 execution thread I have these performance results:
ODBC:  does 200 queries in 2 seconds (100.000000 q/s)
libpq: does 200 queries in 3 seconds (66.666667 q/s)

With 2 threads the results are:
ODBC:  does 200 queries in 3 seconds (66.666667 q/s)
Libpq: does 200 queries in 6 seconds (33.333333 q/s)

With 3 threads:
ODBC: does 200 queries in 5 seconds (40.000000 q/s)
Libpq: 200 queries in 9 seconds (22.222222 q/s)

Obviously libpq is slower.

Do you have any ideas why libpq is so much slower than unixODBC?
Where do you think the libpq bottleneck is? Are there any libpq
options (compile time or runtime) that can make it faster?

Respectfully

Constantine


From pgsql-performance-owner@postgresql.org  Sat Jan 21 20:40:41 2006
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To: "Constantine Filin" <cfilin@intermedia.net>
cc: pgsql-performance@postgresql.org
Subject: Re: libpq vs. unixODBC performance 
In-reply-to: <FD6AFE16B92B544E809E0EAC9C8B7850B664D3@ex1.intermedia-inc.net> 
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Comments: In-reply-to "Constantine Filin" <cfilin@intermedia.net>
	message dated "Sat, 21 Jan 2006 15:49:52 -0800"
Date: Sat, 21 Jan 2006 19:40:39 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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"Constantine Filin" <cfilin@intermedia.net> writes:
> Do you have any ideas why libpq is so much slower than unixODBC?

Perhaps ODBC is batching the queries into a transaction behind your
back?  Or preparing them for you?

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sun Jan 22 03:53:42 2006
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Subject: tsearch2 headline and postgresql.conf
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Hi folks,

I'm not sure if this is the right place for this but thought I'd ask.  
I'm relateively new to postgres having only used it on 3 projects and am 
just delving into the setup and admin for the second time.

I decided to try tsearch2 for this project's search requirements but am 
having trouble attaining adequate performance.  I think I've nailed it 
down to trouble with the headline() function in tsearch2. 

In short, there is a crawler that grabs HTML docs and places them in a 
database.  The search is done using tsearch2 pretty much installed 
according to instructions.  I have read a couple online guides suggested 
by this list for tuning the postgresql.conf file.  I only made modest 
adjustments because I'm not working with top-end hardware and am still 
uncertain of the actual impact of the different paramenters.

I've been learning 'explain' and over the course of reading I have done 
enough query tweaking to discover the source of my headache seems to be 
headline().

On a query of 429 documents, of which the avg size of the stripped down 
document as stored is 21KB, and the max is 518KB (an anomaly), tsearch2 
performs exceptionally well returning most queries in about 100ms.

On the other hand, following the tsearch2 guide which suggests returning 
that first portion as a subquery and then generating the headline() from 
those results, I see the query increase to 4 seconds!

This seems to be directly related to document size.  If I filter out 
that 518KB doc along with some 100KB docs by returning "substring( 
stripped_text FROM 0 FOR 50000) AS stripped_text" I decrease the time to 
1.4 seconds, but increase the risk of not getting a headline.

Seeing as how this problem is directly tied to document size, I'm 
wondering if there are any specific settings in postgresql.conf that may 
help, or is this just a fact of life for the headline() function?  Or, 
does anyone know what the problem is and how to overcome it?

From pgsql-performance-owner@postgresql.org  Sun Jan 22 04:25:22 2006
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Date: Sun, 22 Jan 2006 11:24:55 +0300 (MSK)
From: Oleg Bartunov <oleg@sai.msu.su>
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To: pgsql-performance@nullmx.com
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Subject: Re: tsearch2 headline and postgresql.conf
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You didn't provides us any query with explain analyze.
Just to make sure you're fine.

 	Oleg
On Sun, 22 Jan 2006, pgsql-performance@nullmx.com wrote:

> Hi folks,
>
> I'm not sure if this is the right place for this but thought I'd ask.  I'm 
> relateively new to postgres having only used it on 3 projects and am just 
> delving into the setup and admin for the second time.
>
> I decided to try tsearch2 for this project's search requirements but am 
> having trouble attaining adequate performance.  I think I've nailed it down 
> to trouble with the headline() function in tsearch2. 
> In short, there is a crawler that grabs HTML docs and places them in a 
> database.  The search is done using tsearch2 pretty much installed according 
> to instructions.  I have read a couple online guides suggested by this list 
> for tuning the postgresql.conf file.  I only made modest adjustments because 
> I'm not working with top-end hardware and am still uncertain of the actual 
> impact of the different paramenters.
>
> I've been learning 'explain' and over the course of reading I have done 
> enough query tweaking to discover the source of my headache seems to be 
> headline().
>
> On a query of 429 documents, of which the avg size of the stripped down 
> document as stored is 21KB, and the max is 518KB (an anomaly), tsearch2 
> performs exceptionally well returning most queries in about 100ms.
>
> On the other hand, following the tsearch2 guide which suggests returning that 
> first portion as a subquery and then generating the headline() from those 
> results, I see the query increase to 4 seconds!
>
> This seems to be directly related to document size.  If I filter out that 
> 518KB doc along with some 100KB docs by returning "substring( stripped_text 
> FROM 0 FOR 50000) AS stripped_text" I decrease the time to 1.4 seconds, but 
> increase the risk of not getting a headline.
>
> Seeing as how this problem is directly tied to document size, I'm wondering 
> if there are any specific settings in postgresql.conf that may help, or is 
> this just a fact of life for the headline() function?  Or, does anyone know 
> what the problem is and how to overcome it?
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: Have you checked our extensive FAQ?
>
>              http://www.postgresql.org/docs/faq
>

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

From pgsql-performance-owner@postgresql.org  Sun Jan 22 12:04:50 2006
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From: August Zajonc <augustz@augustz.com>
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Alessandro Baretta wrote:
> 
> What I could do relatively easily is instantiate a thread to iteratively
> scan a traditional cursor N rows at a time, retrieving only record keys,
> and finally send them to the query-cache-manager. The application thread
> would then scan through the cursor results by fetching the rows
> associated to a given "page" of keys. I would have to keep the full
> cursor keyset in the application server's session state, but, hopefully,
> this is not nearly as bad as storing the entire recordset.
> 
> Alex
> 
> 
> 

Alessandro,

I've very much enjoyed reading your thoughts and the problem your facing
and everyone's responses.

Since you control the middle layer, could you not use a cookie to keep a
cursor open on the middle layer and tie into it on subsequent queries?

If you are concerned with too many connections open, you could timeout
the sessions quickly and recreate the cursor if someone came back. If
they waited 5 minutes to make the next query, certainly they could wait
a few extra seconds to offset and reacquire a cursor?

The hitlist idea was also a nice one if the size of the data returned is
not overwhelming and does not need to track the underlying db at all
(ie, no refresh).

Mark had a number of good general suggestions though, and I'd like to
echo the materialized views as an option that I could see a lot of uses
for (and have worked around in the past with SELECT INTO's and like).

Interesting stuff.

- August

From pgsql-performance-owner@postgresql.org  Sun Jan 22 16:29:17 2006
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Subject: Re: tsearch2 headline and postgresql.conf
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	<Pine.GSO.4.63.0601221110190.14417@ra.sai.msu.su>
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Oleg Bartunov wrote:

> You didn't provides us any query with explain analyze.
> Just to make sure you're fine.
>
>     Oleg
> On Sun, 22 Jan 2006, pgsql-performance@nullmx.com wrote:
>
>> Hi folks,
>>
>> I'm not sure if this is the right place for this but thought I'd 
>> ask.  I'm relateively new to postgres having only used it on 3 
>> projects and am just delving into the setup and admin for the second 
>> time.
>>
>> I decided to try tsearch2 for this project's search requirements but 
>> am having trouble attaining adequate performance.  I think I've 
>> nailed it down to trouble with the headline() function in tsearch2. 
>> In short, there is a crawler that grabs HTML docs and places them in 
>> a database.  The search is done using tsearch2 pretty much installed 
>> according to instructions.  I have read a couple online guides 
>> suggested by this list for tuning the postgresql.conf file.  I only 
>> made modest adjustments because I'm not working with top-end hardware 
>> and am still uncertain of the actual impact of the different 
>> paramenters.
>>
>> I've been learning 'explain' and over the course of reading I have 
>> done enough query tweaking to discover the source of my headache 
>> seems to be headline().
>>
>> On a query of 429 documents, of which the avg size of the stripped 
>> down document as stored is 21KB, and the max is 518KB (an anomaly), 
>> tsearch2 performs exceptionally well returning most queries in about 
>> 100ms.
>>
>> On the other hand, following the tsearch2 guide which suggests 
>> returning that first portion as a subquery and then generating the 
>> headline() from those results, I see the query increase to 4 seconds!
>>
>> This seems to be directly related to document size.  If I filter out 
>> that 518KB doc along with some 100KB docs by returning "substring( 
>> stripped_text FROM 0 FOR 50000) AS stripped_text" I decrease the time 
>> to 1.4 seconds, but increase the risk of not getting a headline.
>>
>> Seeing as how this problem is directly tied to document size, I'm 
>> wondering if there are any specific settings in postgresql.conf that 
>> may help, or is this just a fact of life for the headline() 
>> function?  Or, does anyone know what the problem is and how to 
>> overcome it?
>>
>
>     Regards,
>         Oleg
> _____________________________________________________________


------------------------

Hi Oleg,

Thanks for taking time to look at this.  Pardon my omission, I was 
writing that email rather late at night.

The following results from 'explain analyze' are from my
devlopment machine which is a dual PIII 600MHz running Debian
Linux and Postgres 8.1.2.  512 MB RAM.  The production machine
yields similar results but it is a virtual server so the
resources are rather unpredictable.  It is a quad processor and
has a larger result set in it's DB.


The original query is:
explain analyze
SELECT url, title, headline(stripped_text,q,
                      'MaxWords=75, MinWords=25, 
StartSel=!!!REPLACE_ME!!!,StopSel=!!!/REPLACE_ME!!!'),
    rank, to_char(timezone('CST', date_last_changed), 'DD Mon YYYY') AS 
date_last_changed
FROM
( SELECT url_id, url, title, stripped_text, date_last_changed, q, 
rank(index_text, q) AS rank
  FROM (web_page w LEFT JOIN url u USING (url_id)), 
to_tsquery('big&search') AS q
  WHERE (index_text <> '') AND (index_text @@ q) AND (w.url_id NOT IN (1,2))
  AND (url NOT LIKE '%badurl.com%')
  ORDER BY rank DESC, date_last_changed DESC
  LIMIT 10 OFFSET 0
) AS useless
;


...and the resultant output of EXPLAIN ANALYZE is:

 Subquery Scan useless  (cost=8.02..8.04 rows=1 width=624) (actual 
time=769.131..2769.320 rows=10 loops=1)
   ->  Limit  (cost=8.02..8.02 rows=1 width=282) (actual 
time=566.798..566.932 rows=10 loops=1)
         ->  Sort  (cost=8.02..8.02 rows=1 width=282) (actual 
time=566.792..566.870 rows=10 loops=1)
               Sort Key: rank(w.index_text, q.q), w.date_last_changed
               ->  Nested Loop  (cost=2.00..8.01 rows=1 width=282) 
(actual time=4.068..563.128 rows=178 loops=1)
                     ->  Nested Loop  (cost=2.00..4.96 rows=1 width=221) 
(actual time=3.179..388.610 rows=179 loops=1)
                           ->  Function Scan on q  (cost=0.00..0.01 
rows=1 width=32) (actual time=0.025..0.028 rows=1 loops=1)
                           ->  Bitmap Heap Scan on web_page w  
(cost=2.00..4.94 rows=1 width=189) (actual time=3.123..387.547 rows=179 
loops=1)
                                 Filter: ((w.index_text <> ''::tsvector) 
AND (w.url_id <> 1) AND (w.url_id <> 2) AND (w.index_text @@ "outer".q))
                                 ->  Bitmap Index Scan on 
idx_index_text  (cost=0.00..2.00 rows=1 width=0) (actual 
time=1.173..1.173 rows=277 loops=1)
                                       Index Cond: (w.index_text @@ 
"outer".q)
                     ->  Index Scan using pk_url on url u  
(cost=0.00..3.03 rows=1 width=65) (actual time=0.044..0.049 rows=1 
loops=179)
                           Index Cond: ("outer".url_id = u.url_id)
                           Filter: (url !~~ '%badurl.com%'::text)
 Total runtime: 2771.023 ms
(15 rows)
-----
Maybe someone can help me with interpreting the ratio of cost to time 
too.  Do they look appropriate?

To give some further data, I've stripped down the query to only return 
what's necessary for examination here.


explain analyze
SELECT headline(stripped_text,q)
FROM
( SELECT stripped_text, q
  FROM (web_page w LEFT JOIN url u USING (url_id)), 
to_tsquery('big&search') AS q
  WHERE (index_text <> '') AND (index_text @@ q) AND (w.url_id NOT IN (1,2))
  LIMIT 10 OFFSET 0
) AS useless
;
 Subquery Scan useless  (cost=43.25..75.50 rows=1 width=64) (actual 
time=383.720..2066.962 rows=10 loops=1)
   ->  Limit  (cost=43.25..75.49 rows=1 width=129) (actual 
time=236.814..258.150 rows=10 loops=1)
         ->  Nested Loop  (cost=43.25..75.49 rows=1 width=129) (actual 
time=236.807..258.070 rows=10 loops=1)
               Join Filter: ("inner".index_text @@ "outer".q)
               ->  Function Scan on q  (cost=0.00..0.01 rows=1 width=32) 
(actual time=0.033..0.033 rows=1 loops=1)
               ->  Merge Right Join  (cost=43.25..70.37 rows=409 
width=151) (actual time=235.603..237.283 rows=31 loops=1)
                     Merge Cond: ("outer".url_id = "inner".url_id)
                     ->  Index Scan using pk_url on url u  
(cost=0.00..806.68 rows=30418 width=4) (actual time=0.029..0.731 rows=39 
loops=1)
                     ->  Sort  (cost=43.25..44.27 rows=409 width=155) 
(actual time=235.523..235.654 rows=31 loops=1)
                           Sort Key: w.url_id
                           ->  Seq Scan on web_page w  (cost=0.00..25.51 
rows=409 width=155) (actual time=0.037..230.577 rows=409 loops=1)
                                 Filter: ((index_text <> ''::tsvector) 
AND (url_id <> 1) AND (url_id <> 2))
 Total runtime: 2081.569 ms
(13 rows)

As a demonstration to note the effect of document size on headline speed 
I've returned only the first 20,000 characters of each document in the 
subquery shown below.  20K is the size of avg document from the results 
with 518K being max (an anomaly), and a few 100K documents.

explain analyze
SELECT headline(stripped_text,q)
FROM
( SELECT substring(stripped_text FROM 0 FOR 20000) AS stripped_text, q
  FROM (web_page w LEFT JOIN url u USING (url_id)), 
to_tsquery('big&search') AS q
  WHERE (index_text <> '') AND (index_text @@ q) AND (w.url_id NOT IN (1,2))
  LIMIT 10 OFFSET 0
) AS useless
;

 Subquery Scan useless  (cost=43.25..75.51 rows=1 width=64) (actual 
time=316.049..906.045 rows=10 loops=1)
   ->  Limit  (cost=43.25..75.49 rows=1 width=129) (actual 
time=239.831..295.151 rows=10 loops=1)
         ->  Nested Loop  (cost=43.25..75.49 rows=1 width=129) (actual 
time=239.825..295.068 rows=10 loops=1)
               Join Filter: ("inner".index_text @@ "outer".q)
               ->  Function Scan on q  (cost=0.00..0.01 rows=1 width=32) 
(actual time=0.021..0.021 rows=1 loops=1)
               ->  Merge Right Join  (cost=43.25..70.37 rows=409 
width=151) (actual time=234.711..236.265 rows=31 loops=1)
                     Merge Cond: ("outer".url_id = "inner".url_id)
                     ->  Index Scan using pk_url on url u  
(cost=0.00..806.68 rows=30418 width=4) (actual time=0.046..0.715 rows=39 
loops=1)
                     ->  Sort  (cost=43.25..44.27 rows=409 width=155) 
(actual time=234.613..234.731 rows=31 loops=1)
                           Sort Key: w.url_id
                           ->  Seq Scan on web_page w  (cost=0.00..25.51 
rows=409 width=155) (actual time=0.030..229.788 rows=409 loops=1)
                                 Filter: ((index_text <> ''::tsvector) 
AND (url_id <> 1) AND (url_id <> 2))
 Total runtime: 907.397 ms
(13 rows)

And finally, returning the whole document without the intervention of 
headline:

explain analyze
SELECT stripped_text
FROM
( SELECT stripped_text, q
  FROM (web_page w LEFT JOIN url u USING (url_id)), 
to_tsquery('big&search') AS q
  WHERE (index_text <> '') AND (index_text @@ q) AND (w.url_id NOT IN (1,2))
  LIMIT 10 OFFSET 0
) AS useless
;

 Subquery Scan useless  (cost=43.25..75.50 rows=1 width=32) (actual 
time=235.218..253.048 rows=10 loops=1)
   ->  Limit  (cost=43.25..75.49 rows=1 width=129) (actual 
time=235.210..252.994 rows=10 loops=1)
         ->  Nested Loop  (cost=43.25..75.49 rows=1 width=129) (actual 
time=235.204..252.953 rows=10 loops=1)
               Join Filter: ("inner".index_text @@ "outer".q)
               ->  Function Scan on q  (cost=0.00..0.01 rows=1 width=32) 
(actual time=0.024..0.024 rows=1 loops=1)
               ->  Merge Right Join  (cost=43.25..70.37 rows=409 
width=151) (actual time=234.008..234.766 rows=31 loops=1)
                     Merge Cond: ("outer".url_id = "inner".url_id)
                     ->  Index Scan using pk_url on url u  
(cost=0.00..806.68 rows=30418 width=4) (actual time=0.058..0.344 rows=39 
loops=1)
                     ->  Sort  (cost=43.25..44.27 rows=409 width=155) 
(actual time=233.896..233.952 rows=31 loops=1)
                           Sort Key: w.url_id
                           ->  Seq Scan on web_page w  (cost=0.00..25.51 
rows=409 width=155) (actual time=0.031..229.057 rows=409 loops=1)
                                 Filter: ((index_text <> ''::tsvector) 
AND (url_id <> 1) AND (url_id <> 2))
 Total runtime: 254.057 ms
(13 rows)


Again, I really appreciate any help you folks can give with this.




From pgsql-performance-owner@postgresql.org  Mon Jan 23 06:19:30 2006
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Subject: Re: [PERFORMANCE] Stored Procedures
From: Marcos <mjs_ops@gmx.net>
To: "Jim C. Nasby" <jnasby@pervasive.com>
Cc: Rikard Pavelic <rikard.pavelic@zg.htnet.hr>,
	pgsql-performance@postgresql.org
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Em Sex, 2006-01-20 �s 15:34 -0600, Jim C. Nasby escreveu:
> On Fri, Jan 20, 2006 at 08:38:23PM +0100, Rikard Pavelic wrote:
> > This would solve problems with prepare which is per session, so for 
> > prepared function to be
> > optimal one must use same connection.
> 
> If you're dealing with something that's performance critical you're not
> going to be constantly re-connecting anyway, so I don't see what the
> issue is.

This one was my doubt, perhaps in based desktop applications this is
true, but in web applications this is not the re-connecting is
constant :(.

Then the preprare not have very advantage because your duration is per
session.

Marcos.


From pgsql-performance-owner@postgresql.org  Mon Jan 23 06:31:25 2006
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August Zajonc wrote:
> Alessandro Baretta wrote:
> 
> Alessandro,
> 
> I've very much enjoyed reading your thoughts and the problem your facing
> and everyone's responses.

Thank you for your interest, Agust.

> Since you control the middle layer, could you not use a cookie to keep a
> cursor open on the middle layer and tie into it on subsequent queries?

I do. The AS/Xcaml calls it "session key". It is usually passed in a cookie for
websites and elsewhere--query string or url--for Intranet/Extranet web
applications. The session information kept by the AS/Xcaml virtual machine
includes cached query results and state information for servlets. I
could--although not terribly easily--also use the Xcaml session manager to
handle allocation of DB connections from the pool, thus allocating one
connection per active session. The session garbage collector would then also
have to manage the recycling of stale DB connections.

> If you are concerned with too many connections open, you could timeout
> the sessions quickly and recreate the cursor if someone came back. If
> they waited 5 minutes to make the next query, certainly they could wait
> a few extra seconds to offset and reacquire a cursor?

Yes I could. Actually, there are quite a few means of handling this issue. The
possible strategies for garbage collecting resources allocated to a remote peer
is are collectively called "failure-detection algorithms" in the theory of
distributed computing. In most cases an "eventually weak failure detector" is
necessary and sufficient to guarantee a number of desirable properties in
asynchronous systems: termination of execution, bounded open connections, and
others.

Yet, it is a theorm that no asynchronous algorithm can be devised to implement
an eventually weak failure detector. This, in turn, implies that no distributed
asynchronous system--i.e. a web application--possesses the above mentioned
desirable properties. Hence, from a theoretical standpoint, we can either choose
to relax the axioms of the system allowing synchronicity--a failure detector
based on a timeout explicitly requires the notion of time--or, as I would
prefer, by eliminating the need for termination of execution--i.e. explicit
client logout--and bounded open connections by delegating to the client the
responsibility of maintaing all relevant state information. Under these
assumptions we can live happily in a perfectly asynchronous stateless world like
that of HTTP.

Now, neither of the two solutions is perfect. In an Intranet/Extranet context, I
want to store server side a significant amount of state information, including
cached query results, thus entailing the need for a synchronous
failure-detector--let's call it "implicit logout detector"--to garbage collect
the stale session files generated by the application. In an open website--no
login--I do not usually want to use sessions, so I prefer to implement the
application so that all relevant state informatoin is maintained by the client.
This model is perfect until we reach the issue of "suspending SELECTs", that is,
limiting the the cardinality of the record set to a configurable "page-size",
allowing the user to page through a vast query result.


> The hitlist idea was also a nice one if the size of the data returned is
> not overwhelming and does not need to track the underlying db at all
> (ie, no refresh).

In an open website, immediate refresh is not critical, so long as I can
guarantee some decent property of data consistency. Full consistency cannot be
achieved, as Tom pointed out. I cordially disagree with Tom on the commandment
that "Thou shalt have no property of consistency other than me". Just like we
have two different transaction isolation levels, guarateeing different degrees
of ACIDity, we could, conceivably wish to formalize a weaker notion of
consistency and implement functionality to match with it, which would not be
possible under the stronger definition property.

> Mark had a number of good general suggestions though, and I'd like to
> echo the materialized views as an option that I could see a lot of uses
> for (and have worked around in the past with SELECT INTO's and like).

I already use materialized views. The database design layer of the AS/Xcaml
allows the definition of fragmented materialized views: the view is split in
fragments, that is, equivalence classes of the record set with respect to the
operation of projection of the view signature to a (small) subset of its
columns. Yet, this actually makes the original problem worse, for materialiazed
view fragments must be garbage collected at some point, thus offering much of
the same conceptual difficulties as cursor pooling strategy.

Alex


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From: "Franklin Haut" <franklin.haut@gmail.com>
To: <pgsql-performance@postgresql.org>
Subject: ENC: RES: pg_dump slow - Solution
Date: Mon, 23 Jan 2006 07:46:27 -0300
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Hi,


Finally i found the problem of slow backup/restore, i=B4m only instaled =
de
Windows 2000 Service Pack 4... :)

Thanks to all


Franklin
=20

-----Mensagem original-----
De: Richard Huxton [mailto:dev@archonet.com] Enviada em: quarta-feira, =
30 de
novembro de 2005 14:28
Para: Franklin Haut
Cc: 'Ron'; pgsql-performance@postgresql.org
Assunto: Re: RES: [PERFORM] pg_dump slow

Franklin Haut wrote:
> Hi,
>=20
> Yes, my problem is that the pg_dump takes 40 secs to complete under=20
> WinXP and 50 minutes under W2K! The same database, the same hardware!, =

> only diferrent Operational Systems.
>=20
> The hardware is:=20
>    Pentium4 HT 3.2 GHz
>    1024 Mb Memory
>    HD 120Gb SATA

There have been reports of very slow network performance on Win2k =
systems
with the default configuration. You'll have to check the archives for
details I'm afraid. This might apply to you.

If you're happy that doesn't affect you then I'd look at the disk system
- perhaps XP has newer drivers than Win2k.

What do the MS performance-charts show is happening? Specifically, CPU =
and
disk I/O.

--
   Richard Huxton
   Archonet Ltd


From pgsql-performance-owner@postgresql.org  Mon Jan 23 08:30:36 2006
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Date: Mon, 23 Jan 2006 13:30:31 +0100
From: Markus Schaber <schabi@logix-tt.com>
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To: pgsql-performance@postgresql.org
Cc: Marcos <mjs_ops@gmx.net>
Subject: Re: [PERFORMANCE] Stored Procedures
References: <43D130EF.3010205@zg.htnet.hr>	
	<20060120191031.GO20182@pervasive.com>
	<43D13C2F.1030203@zg.htnet.hr>	
	<20060120213455.GT20182@pervasive.com>
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Hi, Marcos,

Marcos wrote:

> This one was my doubt, perhaps in based desktop applications this is
> true, but in web applications this is not the re-connecting is
> constant :(.

If this is true, then you have a much bigger performance problem than
query plan preparation.

You really should consider using a connection pool (most web application
servers provide pooling facilities) or some other means to keep the
connection between several http requests.

Worried,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

From pgsql-performance-owner@postgresql.org  Mon Jan 23 11:32:32 2006
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Subject: Re: [PERFORMANCE] Stored Procedures
From: Marcos <mjs_ops@gmx.net>
To: Markus Schaber <schabi@logix-tt.com>
Cc: pgsql-performance@postgresql.org
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Hi Markus

> You really should consider using a connection pool (most web application
> servers provide pooling facilities) or some other means to keep the
> connection between several http requests.

Yes. I'm finding a connection pool, I found the pgpool but yet don't
understand how it's work I'm go read more about him.

Thanks

Marcos


From pgsql-performance-owner@postgresql.org  Mon Jan 23 12:23:52 2006
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From: "Dave Dutcher" <dave@tridecap.com>
To: "'Marcos'" <mjs_ops@gmx.net>
Cc: <pgsql-performance@postgresql.org>
Subject: Re: [PERFORMANCE] Stored Procedures
Date: Mon, 23 Jan 2006 10:23:17 -0600
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I don't think pgpool is what you need.  If I understand pgpool
correctly, pgpool lets you pool multiple postgres servers together.  You
are just looking for database connection pooling.  

A simple connection pool is basically just an application wide list of
connections.  When a client needs a connection, you just request a
connection from the pool.  If there is an unused connection in the pool,
it is given to the client and removed from the unused pool.  If there is
no unused connection in the pool, then a new connection is opened.  When
the client is done with it, the client releases it back into the pool.

You can google for 'database connection pool' and you should find a
bunch of stuff.  It's probably a good idea to find one already written.
If you write your own you have to make sure it can deal with things like
dead connections, synchronization, and maximum numbers of open
connections.

Dave


-----Original Message-----
From: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org] On Behalf Of Marcos
Sent: Monday, January 23, 2006 7:27 AM
To: Markus Schaber
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] [PERFORMANCE] Stored Procedures

Hi Markus

> You really should consider using a connection pool (most web
application
> servers provide pooling facilities) or some other means to keep the
> connection between several http requests.

Yes. I'm finding a connection pool, I found the pgpool but yet don't
understand how it's work I'm go read more about him.

Thanks

Marcos


---------------------------(end of broadcast)---------------------------
TIP 4: Have you searched our list archives?

               http://archives.postgresql.org


From pgsql-performance-owner@postgresql.org  Mon Jan 23 13:24:48 2006
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Date: Mon, 23 Jan 2006 11:25:26 -0600
From: Frank Wiles <frank@wiles.org>
To: "Dave Dutcher" <dave@tridecap.com>
Cc: mjs_ops@gmx.net, pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Stored Procedures
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On Mon, 23 Jan 2006 10:23:17 -0600
"Dave Dutcher" <dave@tridecap.com> wrote:

> I don't think pgpool is what you need.  If I understand pgpool
> correctly, pgpool lets you pool multiple postgres servers together.
> You are just looking for database connection pooling.  

  While pgpool can let you pool together multiple backend servers,
  it also functions well as just a connection pooling device with
  only one backend. 

 ---------------------------------
   Frank Wiles <frank@wiles.org>
   http://www.wiles.org
 ---------------------------------


From pgsql-performance-owner@postgresql.org  Mon Jan 23 15:19:18 2006
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To: =?ISO-8859-1?Q?=DCmit_=D6ztosun?= <umit@likyabilisim.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow queries consisting inner selects and order bys & hack to
	speed up
In-reply-to: <d95439ec0601211255y4ac7ad91yeb7c9beb76e3e57c@mail.gmail.com> 
References: <d95439ec0601211255y4ac7ad91yeb7c9beb76e3e57c@mail.gmail.com>
Comments: In-reply-to =?ISO-8859-1?Q?=DCmit_=D6ztosun?=
 <umit@likyabilisim.com>
	message dated "Sat, 21 Jan 2006 22:55:23 +0200"
Date: Mon, 23 Jan 2006 14:19:14 -0500
Message-ID: <7599.1138043954@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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=?ISO-8859-1?Q?=DCmit_=D6ztosun?= <umit@likyabilisim.com> writes:
> Our application uses typical queries similar to following (very simplified):

> SELECT
>  part_id,
>  part_name,
>  (SELECT
>   SUM(amount) FROM part_movements M
>   WHERE P.part_id =3D M.part_id
>  ) as part_amount
> FROM parts P
> ORDER BY part_name
> LIMIT 50

> Postgres seems to compute all possible rows and then sorts the
> results, which nearly renders the paging meaningless.

Yeah.  The general rule is that sorting happens after computing the
SELECT values --- this is more or less required for cases where the
ORDER BY refers to a SELECT-list item.  You'd probably have better
results by writing a sub-select:

SELECT
 part_id,
 part_name,
 (SELECT
  SUM(amount) FROM part_movements M
  WHERE P.part_id = M.part_id
 ) as part_amount
FROM
 (SELECT part_id, part_name FROM parts P
  WHERE whatever ORDER BY whatever LIMIT n) as P;

This will do the part_movements stuff only for rows that make it out of
the sub-select.

Another approach is to make sure the ORDER BY is always on an indexed
column; in cases where the ORDER BY is done by an indexscan instead
of a sort, calculation of the unwanted SELECT-list items does not
happen.  However, this only works as long as LIMIT+OFFSET is fairly
small.

Lastly, are you on a reasonably current Postgres version (performance
complaints about anything older than 8.0 will no longer be accepted
with much grace), and are your statistics up to date?  The ANALYZE
shows rowcount estimates that seem suspiciously far off:

        ->  Seq Scan on scf_stokkart stok  (cost=0.00..142622.54 rows=25 width=503) (actual time=4.726..19324.633 rows=4947 loops=1)
              Filter: (upper((durum)::text) = 'A'::text)

This is important because, if the planner realized that the SELECT-list
items were going to be evaluated 5000 times not 25, it might well choose
a different plan.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 23 18:06:03 2006
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I'm investigating a potential IO issue.  We're running 7.4 on AIX 5.1.  
During periods of high activity (reads, writes, and vacuums), we are 
seeing iostat reporting 100% disk usage.  I have a feeling that the 
iostat numbers are misleading.  I can make iostat usage jump from less 
than 10% to greater than 95% by running a single vacuum against a 
moderate sized table (no noticeable change in the other activity).

Do I actually have a problem with IO?  Whether I do or not, at what 
point should I start to be concerned about IO problems?  If my 
understanding is correct, it should be based on the wait time.  Here's 
the output of vmstat during heavy load (reads, writes, several daily 
vacuums and a nightly pg_dump).  Wait times appear to be alright, but my 
understanding of when to start being concerned about IO starvation is 
foggy at best.

vmstat 5
kthr     memory             page              faults        cpu
----- ----------- ------------------------ ------------ -----------
r  b   avm   fre  re  pi  po  fr   sr  cy  in   sy  cs us sy id wa
2  2 1548418 67130   0   0   0 141   99   0 1295 22784 13128 11  4 71 14
3  3 1548422 66754   0   0   0 2127 2965   0 2836 29981 25091 26  4 39 31
2  3 1548423 66908   0   0   0 2369 3221   0 3130 34725 28424 25  7 38 30
3  5 1548423 67029   0   0   0 2223 3097   0 2722 31885 25929 26  9 33 32
3  3 1548423 67066   0   0   0 2366 3194   0 2824 43546 36226 30  5 35 31
2  4 1548423 67004   0   0   0 2123 3236   0 2662 25756 21841 22  4 39 35
2  4 1548957 66277   0   0   0 1928 10322   0 2941 36340 29906 28  6 34 33
3  5 1549245 66024   0   0   0 2324 14291   0 2872 39413 25615 25  4 34 37
2  6 1549282 66107   0   0   0 1930 11189   0 2832 72062 32311 26  5 32 38
2  4 1549526 65855   0   0   0 2375 9278   0 2822 40368 32156 29  5 37 29
2  3 1548984 66227   0   0   0 1732 5065   0 2825 39240 30788 26  5 40 30
3  4 1549341 66027   0   0   0 2325 6453   0 2790 37567 30509 28  5 37 30
2  4 1549377 65789   0   0   0 1633 2731   0 2648 35533 27395 20  5 39 36
1  5 1549765 65666   0   0   0 2272 3340   0 2792 43002 34090 26  5 29 40
2  3 1549787 65646   0   0   0 1779 2679   0 2596 37446 29184 22  5 37 36
2  5 1548985 66263   0   0   0 2077 3086   0 2778 49579 39940 26  9 35 30
2  4 1548985 66473   0   0   0 2078 3093   0 2682 23274 18460 22  3 41 34
4  3 1548985 66263   0   0   0 2177 3344   0 2734 43029 35536 29  5 38 28
1  4 1548985 66491   0   0   0 1978 3215   0 2739 28291 22672 23  4 41 32
3  3 1548985 66422   0   0   0 1732 2469   0 2852 71865 30850 28  5 38 29

-- 
Brad Nicholson  416-673-4106
Database Administrator, Afilias Canada Corp.



From pgsql-performance-owner@postgresql.org  Tue Jan 24 12:41:17 2006
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Brad Nicholson wrote:
> I'm investigating a potential IO issue.  We're running 7.4 on AIX 
> 5.1.  During periods of high activity (reads, writes, and vacuums), we 
> are seeing iostat reporting 100% disk usage.  I have a feeling that 
> the iostat numbers are misleading.  I can make iostat usage jump from 
> less than 10% to greater than 95% by running a single vacuum against a 
> moderate sized table (no noticeable change in the other activity).
>
Well that isn't surprising. Vacuum is brutal especially on 7.4 as that 
is pre background writer. What type of IO do you have available (RAID, 
SCSI?)

> Do I actually have a problem with IO?  Whether I do or not, at what 
> point should I start to be concerned about IO problems?  If my 
> understanding is correct, it should be based on the wait time.  Here's 
> the output of vmstat during heavy load (reads, writes, several daily 
> vacuums and a nightly pg_dump).  Wait times appear to be alright, but 
> my understanding of when to start being concerned about IO starvation 
> is foggy at best.
>
> vmstat 5
> kthr     memory             page              faults        cpu
> ----- ----------- ------------------------ ------------ -----------
> r  b   avm   fre  re  pi  po  fr   sr  cy  in   sy  cs us sy id wa
> 2  2 1548418 67130   0   0   0 141   99   0 1295 22784 13128 11  4 71 14
> 3  3 1548422 66754   0   0   0 2127 2965   0 2836 29981 25091 26  4 39 31
> 2  3 1548423 66908   0   0   0 2369 3221   0 3130 34725 28424 25  7 38 30
> 3  5 1548423 67029   0   0   0 2223 3097   0 2722 31885 25929 26  9 33 32
> 3  3 1548423 67066   0   0   0 2366 3194   0 2824 43546 36226 30  5 35 31
> 2  4 1548423 67004   0   0   0 2123 3236   0 2662 25756 21841 22  4 39 35
> 2  4 1548957 66277   0   0   0 1928 10322   0 2941 36340 29906 28  6 
> 34 33
> 3  5 1549245 66024   0   0   0 2324 14291   0 2872 39413 25615 25  4 
> 34 37
> 2  6 1549282 66107   0   0   0 1930 11189   0 2832 72062 32311 26  5 
> 32 38
> 2  4 1549526 65855   0   0   0 2375 9278   0 2822 40368 32156 29  5 37 29
> 2  3 1548984 66227   0   0   0 1732 5065   0 2825 39240 30788 26  5 40 30
> 3  4 1549341 66027   0   0   0 2325 6453   0 2790 37567 30509 28  5 37 30
> 2  4 1549377 65789   0   0   0 1633 2731   0 2648 35533 27395 20  5 39 36
> 1  5 1549765 65666   0   0   0 2272 3340   0 2792 43002 34090 26  5 29 40
> 2  3 1549787 65646   0   0   0 1779 2679   0 2596 37446 29184 22  5 37 36
> 2  5 1548985 66263   0   0   0 2077 3086   0 2778 49579 39940 26  9 35 30
> 2  4 1548985 66473   0   0   0 2078 3093   0 2682 23274 18460 22  3 41 34
> 4  3 1548985 66263   0   0   0 2177 3344   0 2734 43029 35536 29  5 38 28
> 1  4 1548985 66491   0   0   0 1978 3215   0 2739 28291 22672 23  4 41 32
> 3  3 1548985 66422   0   0   0 1732 2469   0 2852 71865 30850 28  5 38 29
>


From pgsql-performance-owner@postgresql.org  Tue Jan 24 13:04:00 2006
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Joshua D. Drake wrote:

> Brad Nicholson wrote:
>
>> I'm investigating a potential IO issue.  We're running 7.4 on AIX 
>> 5.1.  During periods of high activity (reads, writes, and vacuums), 
>> we are seeing iostat reporting 100% disk usage.  I have a feeling 
>> that the iostat numbers are misleading.  I can make iostat usage jump 
>> from less than 10% to greater than 95% by running a single vacuum 
>> against a moderate sized table (no noticeable change in the other 
>> activity).
>>
> Well that isn't surprising. Vacuum is brutal especially on 7.4 as that 
> is pre background writer. What type of IO do you have available (RAID, 
> SCSI?)
>
Data LUN is RAID 10, wal LUN is RAID 1.


-- 
Brad Nicholson  416-673-4106    bnichols@ca.afilias.info
Database Administrator, Afilias Canada Corp.



From pgsql-performance-owner@postgresql.org  Tue Jan 24 13:07:42 2006
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To: Brad Nicholson <bnichols@ca.afilias.info>
cc: pgsql-performance@postgresql.org
Subject: Re: Investigating IO Saturation 
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Comments: In-reply-to Brad Nicholson <bnichols@ca.afilias.info>
	message dated "Tue, 24 Jan 2006 11:35:02 -0500"
Date: Tue, 24 Jan 2006 12:07:38 -0500
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Brad Nicholson <bnichols@ca.afilias.info> writes:
> I'm investigating a potential IO issue.  We're running 7.4 on AIX 5.1.  
> During periods of high activity (reads, writes, and vacuums), we are 
> seeing iostat reporting 100% disk usage.  I have a feeling that the 
> iostat numbers are misleading.  I can make iostat usage jump from less 
> than 10% to greater than 95% by running a single vacuum against a 
> moderate sized table (no noticeable change in the other activity).

That's not particularly surprising, and I see no reason to think that
iostat is lying to you.

More recent versions of PG include parameters that you can use to
"throttle" vacuum's I/O demand ... but unthrottled, it's definitely
an I/O hog.

The vmstat numbers suggest that vacuum is not completely killing you,
but you could probably get some improvement in foreground query
performance by throttling it back.  There are other good reasons to
consider an update, anyway.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Tue Jan 24 13:08:43 2006
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Brad Nicholson wrote:
> Joshua D. Drake wrote:
>
>> Brad Nicholson wrote:
>>
>>> I'm investigating a potential IO issue.  We're running 7.4 on AIX 
>>> 5.1.  During periods of high activity (reads, writes, and vacuums), 
>>> we are seeing iostat reporting 100% disk usage.  I have a feeling 
>>> that the iostat numbers are misleading.  I can make iostat usage 
>>> jump from less than 10% to greater than 95% by running a single 
>>> vacuum against a moderate sized table (no noticeable change in the 
>>> other activity).
>>>
>> Well that isn't surprising. Vacuum is brutal especially on 7.4 as 
>> that is pre background writer. What type of IO do you have available 
>> (RAID, SCSI?)
>>
> Data LUN is RAID 10, wal LUN is RAID 1.
How many disks?

>
>


From pgsql-performance-owner@postgresql.org  Sun Jan 29 23:29:03 2006
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Date: Tue, 24 Jan 2006 19:40:22 +0100
From: Arnau Rebassa Villalonga <arebassa@androme.es>
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Hi all,

   I have a performance problem and I don't know where is my bottleneck.
I have postgresql 7.4.2 running on a debian server with kernel
2.4.26-1-686-smp with two Xeon(TM) at 2.80GHz and 4GB of RAM and a RAID
5 made with SCSI disks. Maybe its not the latest hardware but I think
it's not that bad.

   My problem is that the general performance is not good enough and I
don't know where is the bottleneck. It could be because the queries are
not optimized as they should be, but I also think it can be a postgresql
configuration problem or hardware problem (HDs not beeing fast enough,
not enough RAM, ... )

   The configuration of postgresql is the default, I tried to tune the
postgresql.conf and the results where disappointing, so I left again the
default values.

When I do top I get:
top - 19:10:24 up 452 days, 15:48,  4 users,  load average: 6.31, 6.27, 6.52
Tasks:  91 total,   8 running,  83 sleeping,   0 stopped,   0 zombie
Cpu(s):  24.8% user,  15.4% system,   0.0% nice,  59.9% idle
Mem:   3748956k total,  3629252k used,   119704k free,    57604k buffers
Swap:  2097136k total,    14188k used,  2082948k free,  3303620k cached

   Most of the time the idle value is even higher than 60%.

I know it's a  problem with a very big scope, but could you give me a
hint about where I should look to?


Thank you very much
-- 
Arnau


From pgsql-performance-owner@postgresql.org  Tue Jan 24 16:04:07 2006
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tgl@sss.pgh.pa.us (Tom Lane) writes:

> Brad Nicholson <bnichols@ca.afilias.info> writes:
>> I'm investigating a potential IO issue.  We're running 7.4 on AIX 5.1.  
>> During periods of high activity (reads, writes, and vacuums), we are 
>> seeing iostat reporting 100% disk usage.  I have a feeling that the 
>> iostat numbers are misleading.  I can make iostat usage jump from less 
>> than 10% to greater than 95% by running a single vacuum against a 
>> moderate sized table (no noticeable change in the other activity).
>
> That's not particularly surprising, and I see no reason to think that
> iostat is lying to you.
>
> More recent versions of PG include parameters that you can use to
> "throttle" vacuum's I/O demand ... but unthrottled, it's definitely
> an I/O hog.

I believe it's 7.4 where the cost-based vacuum parameters entered in,
so that would, in principle, already be an option.

[rummaging around...]

Hmm.... There was a patch for 7.4, but it's only "standard" as of
8.0...

> The vmstat numbers suggest that vacuum is not completely killing you,
> but you could probably get some improvement in foreground query
> performance by throttling it back.  There are other good reasons to
> consider an update, anyway.

I'd have reservations about "throttling it back" because that would
lead to VACUUMs running, and holding transactions open, for 6 hours
instead of 2.

That is consistent with benchmarking; there was a report of the
default policy cutting I/O load by ~80% at the cost of vacuums taking
3x as long to complete.

The "real" answer is to move to 8.x, where VACUUM doesn't chew up
shared memory cache as it does in 7.4 and earlier.

But in the interim, we need to make sure we tilt over the right
windmills, or something of the sort :-).
-- 
output = reverse("gro.gultn" "@" "enworbbc")
http://www3.sympatico.ca/cbbrowne/linuxxian.html
"Women and cats will do as  they please, and men and dogs should relax
and get used to the idea." -- Robert A. Heinlein

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To: pgsql-performance@postgresql.org
Subject: Re: Investigating IO Saturation
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On Tue, Jan 24, 2006 at 02:43:59PM -0500, Chris Browne wrote:
> I believe it's 7.4 where the cost-based vacuum parameters entered in,
> so that would, in principle, already be an option.
> 
> [rummaging around...]
> 
> Hmm.... There was a patch for 7.4, but it's only "standard" as of
> 8.0...

And it doesn't work very well without changes to buffering.  You need
both pieces to get it to work.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism. 
                --Brad Holland

From pgsql-performance-owner@postgresql.org  Tue Jan 24 19:19:40 2006
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From: "Daniel Gish" <dan@centrifugesolutions.com>
To: <pgsql-performance@postgresql.org>
Subject: Inconsistant query plan
Date: Tue, 24 Jan 2006 16:15:57 -0700
Message-ID: <GJEAKHIALCNFPPGBGEKNEEBDDGAA.dan@centrifugesolutions.com>
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Hi,
We are running Postgresql 8.1, and getting dramatically inconsistant results
after running VACUUM ANALYZE.  Sometimes after analyzing the database, the
query planner chooses a very efficient plan (15 rows, 4.744 ms), and
sometimes a terrible one (24 rows, 3536.995 ms).  Here's the abbreviated
query:

SELECT * FROM t1 INNER JOIN (t2 INNER JOIN (t3 INNER JOIN t4 ON t3.gid =
t4.gid) ON t3.gid = t2.gid) ON t2.eid = t1.eid WHERE ...

In the efficient plan, t2 is joined to t3 & t4 before being joined to t1.
The inefficient plan joins t1 to t2 before joining to the other tables.

We've experimented with different settings, such as shared_buffers &
max_fsm_pages, to no avail.  Anybody have a suggestion for getting the
efficient plan to execute consistantly?  If you'd like to see the actual
query & query plans let me know.

Best Regards,
Dan



From pgsql-performance-owner@postgresql.org  Tue Jan 24 19:30:17 2006
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Subject: Re: Inconsistant query plan
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Daniel Gish <dan@centrifugesolutions.com>
Cc: pgsql-performance@postgresql.org
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On Tue, 2006-01-24 at 17:15, Daniel Gish wrote:
> Hi,
> We are running Postgresql 8.1, and getting dramatically inconsistant results
> after running VACUUM ANALYZE.  Sometimes after analyzing the database, the
> query planner chooses a very efficient plan (15 rows, 4.744 ms), and
> sometimes a terrible one (24 rows, 3536.995 ms).  Here's the abbreviated
> query:
> 
> SELECT * FROM t1 INNER JOIN (t2 INNER JOIN (t3 INNER JOIN t4 ON t3.gid =
> t4.gid) ON t3.gid = t2.gid) ON t2.eid = t1.eid WHERE ...
> 
> In the efficient plan, t2 is joined to t3 & t4 before being joined to t1.
> The inefficient plan joins t1 to t2 before joining to the other tables.
> 
> We've experimented with different settings, such as shared_buffers &
> max_fsm_pages, to no avail.  Anybody have a suggestion for getting the
> efficient plan to execute consistantly?  If you'd like to see the actual
> query & query plans let me know.

Have you adjusted the stats target for that column?  See \h alter table
in psql for the syntax for that.  Then run analyze again.

From pgsql-performance-owner@postgresql.org  Tue Jan 24 19:59:07 2006
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From: Michael Fuhr <mike@fuhr.org>
To: Daniel Gish <dan@centrifugesolutions.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Inconsistant query plan
Message-ID: <20060124235857.GA92385@winnie.fuhr.org>
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On Tue, Jan 24, 2006 at 04:15:57PM -0700, Daniel Gish wrote:
> We are running Postgresql 8.1, and getting dramatically inconsistant results
> after running VACUUM ANALYZE.  Sometimes after analyzing the database, the
> query planner chooses a very efficient plan (15 rows, 4.744 ms), and
> sometimes a terrible one (24 rows, 3536.995 ms).  Here's the abbreviated
> query:
> 
> SELECT * FROM t1 INNER JOIN (t2 INNER JOIN (t3 INNER JOIN t4 ON t3.gid =
> t4.gid) ON t3.gid = t2.gid) ON t2.eid = t1.eid WHERE ...

How abbreviated is that example?  Are you actually joining more
tables than that?  In another recent thread varying plans were
attributed to exceeding geqo_threshold:

http://archives.postgresql.org/pgsql-performance/2006-01/msg00132.php

Does your situation look similar?

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Tue Jan 24 21:02:10 2006
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Subject: Re: Inconsistant query plan
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Hi,
Thanks for your response.  The actual query is below; the joins are only 4
deep.  Adjusting the stats target did help, but not dramatically.


EFFICIENT PLAN:

# explain analyze SELECT ev.eid FROM events ev INNER JOIN (events_join ej
INNER JOIN (groups_join gj INNER JOIN groups g ON gj.gid = g.gid) ON ej.gid
= gj.gid) ON ev.eid = ej.eid  WHERE ev.status > 0 AND ej.type_id = 1 AND
g.deleted = 'f' AND g.deactivated != 't' AND ev.type_id >= 0 AND gj.uid=3
AND ev.timestart BETWEEN '01/23/2006'::timestamp AND '02/23/2006'::timestamp
+ '1 day - 1 minute';
                                                                            
              QUERY PLAN
----------------------------------------------------------------------------
----------------------------------------------------------------------------
---------------------------------------
 Nested Loop  (cost=0.00..8370.41 rows=25 width=4) (actual time=4.510..4.510
rows=0 loops=1)
   ->  Nested Loop  (cost=0.00..6124.63 rows=673 width=4) (actual
time=0.132..3.116 rows=92 loops=1)
         ->  Nested Loop  (cost=0.00..70.95 rows=8 width=8) (actual
time=0.080..2.226 rows=19 loops=1)
               ->  Index Scan using groups_join_uid_idx on groups_join gj
(cost=0.00..16.27 rows=11 width=4) (actual time=0.019..0.471 rows=196
loops=1)
                     Index Cond: (uid = 3)
               ->  Index Scan using groups_pkey on groups g
(cost=0.00..4.96 rows=1 width=4) (actual time=0.005..0.006 rows=0 loops=196)
                     Index Cond: ("outer".gid = g.gid)
                     Filter: ((NOT deleted) AND (deactivated <> true))
         ->  Index Scan using events_join_gid_idx on events_join ej
(cost=0.00..752.45 rows=341 width=8) (actual time=0.010..0.027 rows=5
loops=19)
               Index Cond: (ej.gid = "outer".gid)
               Filter: (type_id = 1)
   ->  Index Scan using events_pkey on events ev  (cost=0.00..3.32 rows=1
width=4) (actual time=0.012..0.012 rows=0 loops=92)
         Index Cond: (ev.eid = "outer".eid)
         Filter: ((status > 0) AND (type_id >= 0) AND (timestart >=
'2006-01-23 00:00:00'::timestamp without time zone) AND (timestart <=
'2006-02-23 23:59:00'::timestamp without time zone))
 Total runtime: 4.744 ms
(15 rows)


INEFFICIENT PLAN:

# explain analyze SELECT ev.eid FROM events ev INNER JOIN (events_join ej
INNER JOIN (groups_join gj INNER JOIN groups g ON gj.gid = g.gid) ON ej.gid
= g.gid) ON ev.eid = ej.eid  WHERE ev.status > 0 AND ej.type_id = 1 AND
g.deleted = 'f' AND g.deactivated != 't' AND ev.type_id >= 0 AND gj.uid=3
AND ev.timestart BETWEEN '01/23/2006'::timestamp AND '02/23/2006'::timestamp
+ '1 day - 1 minute';
                                                                            
              QUERY PLAN
----------------------------------------------------------------------------
----------------------------------------------------------------------------
---------------------------------------
 Nested Loop  (cost=978.19..37161.81 rows=133 width=4) (actual
time=2511.676..2511.676 rows=0 loops=1)
   ->  Merge Join  (cost=978.19..22854.00 rows=4244 width=4) (actual
time=1718.420..2510.128 rows=92 loops=1)
         Merge Cond: ("outer".gid = "inner".gid)
         ->  Index Scan using events_join_gid_idx on events_join ej
(cost=0.00..23452.59 rows=740598 width=8) (actual time=0.014..1532.447
rows=626651 loops=1)
               Filter: (type_id = 1)
         ->  Sort  (cost=978.19..978.47 rows=113 width=8) (actual
time=2.371..2.540 rows=101 loops=1)
               Sort Key: g.gid
               ->  Nested Loop  (cost=0.00..974.33 rows=113 width=8) (actual
time=0.078..2.305 rows=19 loops=1)
                     ->  Index Scan using groups_join_uid_idx on groups_join
gj  (cost=0.00..182.65 rows=159 width=4) (actual time=0.017..0.485 rows=196
loops=1)
                           Index Cond: (uid = 3)
                     ->  Index Scan using groups_pkey on groups g
(cost=0.00..4.97 rows=1 width=4) (actual time=0.006..0.006 rows=0 loops=196)
                           Index Cond: ("outer".gid = g.gid)
                           Filter: ((NOT deleted) AND (deactivated <> true))
   ->  Index Scan using events_pkey on events ev  (cost=0.00..3.36 rows=1
width=4) (actual time=0.013..0.013 rows=0 loops=92)
         Index Cond: (ev.eid = "outer".eid)
         Filter: ((status > 0) AND (type_id >= 0) AND (timestart >=
'2006-01-23 00:00:00'::timestamp without time zone) AND (timestart <=
'2006-02-23 23:59:00'::timestamp without time zone))
 Total runtime: 2511.920 ms
(17 rows)

Regards,
Dan




From pgsql-performance-owner@postgresql.org  Wed Jan 25 05:05:47 2006
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Daniel Gish wrote:
> Hi,
> Thanks for your response.  The actual query is below; the joins are only 4
> deep.  Adjusting the stats target did help, but not dramatically.
>                                                                           
>               QUERY PLAN
> ----------------------------------------------------------------------------
> ----------------------------------------------------------------------------
> ---------------------------------------
>  Nested Loop  (cost=978.19..37161.81 rows=133 width=4) (actual
> time=2511.676..2511.676 rows=0 loops=1)
>    ->  Merge Join  (cost=978.19..22854.00 rows=4244 width=4) (actual
> time=1718.420..2510.128 rows=92 loops=1)
 > ...
 >               ->  Nested Loop  (cost=0.00..974.33 rows=113 width=8) (actual
time=0.078..2.305 rows=19 loops=1)

I have a similar problem recently. An importat diagnostic tool for these issues 
is the pg_stats view. Let me suggest that you post the relevant lines from 
pg_stats, so that with some help you will be able to discover what data advises 
the query planner to overestimate the cardinality of some joins and 
underestimate others.


Alex


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From pgsql-performance-owner@postgresql.org  Wed Jan 25 08:01:36 2006
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Date: Wed, 25 Jan 2006 15:01:34 +0300
From: Evgeny Gridasov <eugrid@fpm.kubsu.ru>
To: pgsql-performance@postgresql.org
Subject: DB responce during DB dump
Message-Id: <20060125150134.55589806.eugrid@fpm.kubsu.ru>
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Hi, everybody!

I experience problems with backing up one of my Postgresql 8.1.2 installations.
The problem is that when I do DB backup, all queries begin to run very slow =(
The database only grows in its size (~20Gb today), and the number of transactions increases every month.
A year ago such slow down was OK, but today it is unacceptable.

I found out that pg_dump dramatically increases hdd I/O and because of this most of all
queries begin to run slower. My application using this DB server is time-critical, so
any kind of slow down is critical.

I've written a perl script to limit pg_dump output bandwidth, a simple traffic shaper,
which runs as: pg_dumpall -c -U postgres | limit_bandwidth.pl | bzip2 > pgsql_dump.bz2
The limit_bandwidth.pl script limits pipe output at 4Mb/sec rate, which seems to be ok.

Is there any other solution to avoid this problem?


-- 
Evgeny Gridasov
Software Engineer 
I-Free, Russia

From pgsql-performance-owner@postgresql.org  Wed Jan 25 08:44:46 2006
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From: Richard Huxton <dev@archonet.com>
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To: Evgeny Gridasov <eugrid@fpm.kubsu.ru>
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Subject: Re: DB responce during DB dump
References: <GJEAKHIALCNFPPGBGEKNEEBDDGAA.dan@centrifugesolutions.com>
	<20060125150134.55589806.eugrid@fpm.kubsu.ru>
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Evgeny Gridasov wrote:
> Hi, everybody!
> 
> I experience problems with backing up one of my Postgresql 8.1.2 installations.
> The problem is that when I do DB backup, all queries begin to run very slow =(
> The database only grows in its size (~20Gb today), and the number of transactions increases every month.
> A year ago such slow down was OK, but today it is unacceptable.
> 
> I found out that pg_dump dramatically increases hdd I/O and because of this most of all
> queries begin to run slower. My application using this DB server is time-critical, so
> any kind of slow down is critical.
> 
> I've written a perl script to limit pg_dump output bandwidth, a simple traffic shaper,
> which runs as: pg_dumpall -c -U postgres | limit_bandwidth.pl | bzip2 > pgsql_dump.bz2
> The limit_bandwidth.pl script limits pipe output at 4Mb/sec rate, which seems to be ok.
> 
> Is there any other solution to avoid this problem?

That's an interesting solution, and I'd guess people might like to see 
it posted to the list if it's not too big.

Also, there's no reason you have to dump from the same machine, you can 
do so over the network which should reduce activity a little bit.

Basically though, it sounds like you either need more disk I/O or a 
different approach.

Have you looked into using PITR log-shipping or replication (e.g. slony) 
to have an off-machine backup?

-- 
   Richard Huxton
   Archonet Ltd

From pgsql-performance-owner@postgresql.org  Sun Jan 29 23:29:07 2006
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From: Jen Sale <js@slipt.net>
To: pgsql-performance@postgresql.org
Subject: Desperate: View not using indexes (very slow)
Date: Wed, 25 Jan 2006 11:09:25 -0500
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We recently segmented a large table into calendar month slices and were going 
to to replace the original, but we are not getting the results we think it 
should...  Everything is vacuumed, and we are using 8.0.3 on amd64.

Anything anyone can suggest would be appreciated, our backs against the wall.

=> explain select suck_id from sucks_new where suck_id in ( select id as 
suck_id from saved_cart_items where 
publish_id='60160b57a1969fa228ae3470fbe7a50a' );
                                                                                                   
QUERY PLAN 
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop IN Join  (cost=5311290.80..7124499.86 rows=5472 width=32)
   Join Filter: ("outer".suck_id = "inner".id)
   ->  Subquery Scan sucks_new  (cost=5309907.40..6181642.53 rows=13947762 
width=32)
         ->  Unique  (cost=5309907.40..6042164.91 rows=13947762 width=212)
               ->  Sort  (cost=5309907.40..5344776.81 rows=13947762 width=212)
                     Sort Key: suck_id, sitenum
                     ->  Append  (cost=0.00..632289.24 rows=13947762 
width=212)
                           ->  Subquery Scan "*SELECT* 
1"  (cost=0.00..83767.54 rows=1703577 width=209)
                                 ->  Seq Scan on sucks_2006_01  
(cost=0.00..66731.77 rows=1703577 width=209)
                           ->  Subquery Scan "*SELECT* 
2"  (cost=0.00..93670.20 rows=2081560 width=209)
                                 ->  Seq Scan on sucks_2005_12  
(cost=0.00..72854.60 rows=2081560 width=209)
                           ->  Subquery Scan "*SELECT* 
3"  (cost=0.00..91311.16 rows=2021958 width=210)
                                 ->  Seq Scan on sucks_2005_11  
(cost=0.00..71091.58 rows=2021958 width=210)
                           ->  Subquery Scan "*SELECT* 
4"  (cost=0.00..85510.34 rows=1886417 width=211)
                                 ->  Seq Scan on sucks_2005_10  
(cost=0.00..66646.17 rows=1886417 width=211)
                           ->  Subquery Scan "*SELECT* 
5"  (cost=0.00..74216.38 rows=1642719 width=210)
                                 ->  Seq Scan on sucks_2005_09  
(cost=0.00..57789.19 rows=1642719 width=210)
                           ->  Subquery Scan "*SELECT* 
6"  (cost=0.00..64346.12 rows=1429106 width=209)
                                 ->  Seq Scan on sucks_2005_08  
(cost=0.00..50055.06 rows=1429106 width=209)
                           ->  Subquery Scan "*SELECT* 
7"  (cost=0.00..76449.66 rows=1709283 width=209)
                                 ->  Seq Scan on sucks_2005_07  
(cost=0.00..59356.83 rows=1709283 width=209)
                           ->  Subquery Scan "*SELECT* 
8"  (cost=0.00..63017.84 rows=1473142 width=212)
                                 ->  Seq Scan on sucks_2005_06 
"local"  (cost=0.00..48286.42 rows=1473142 width=212)
   ->  Materialize  (cost=1383.39..1383.60 rows=20 width=12)
         ->  Seq Scan on saved_cart_items  (cost=0.00..1383.38 rows=20 
width=12)
               Filter: (publish_id = 
'60160b57a1969fa228ae3470fbe7a50a'::bpchar)

as opposed to 

=> explain select suck_id from sucks_new where suck_id=7136642;                                                                                                 
QUERY PLAN 
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Subquery Scan sucks_new  (cost=46.22..46.72 rows=8 width=32)
   ->  Unique  (cost=46.22..46.64 rows=8 width=212)
         ->  Sort  (cost=46.22..46.24 rows=8 width=212)
               Sort Key: suck_id, sitenum
               ->  Append  (cost=0.00..46.10 rows=8 width=212)
                     ->  Subquery Scan "*SELECT* 1"  (cost=0.00..5.64 rows=1 
width=209)
                           ->  Index Scan using sucks_2006_01_pkey on 
sucks_2006_01  (cost=0.00..5.63 rows=1 width=209)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 2"  (cost=0.00..5.95 rows=1 
width=209)
                           ->  Index Scan using sucks_2005_12_pkey on 
sucks_2005_12  (cost=0.00..5.94 rows=1 width=209)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 3"  (cost=0.00..5.21 rows=1 
width=210)
                           ->  Index Scan using sucks_2005_11_pkey on 
sucks_2005_11  (cost=0.00..5.20 rows=1 width=210)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 4"  (cost=0.00..5.67 rows=1 
width=211)
                           ->  Index Scan using sucks_2005_10_pkey on 
sucks_2005_10  (cost=0.00..5.66 rows=1 width=211)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 5"  (cost=0.00..5.78 rows=1 
width=210)
                           ->  Index Scan using sucks_2005_09_pkey on 
sucks_2005_09  (cost=0.00..5.77 rows=1 width=210)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 6"  (cost=0.00..6.01 rows=1 
width=209)
                           ->  Index Scan using sucks_2005_08_pkey on 
sucks_2005_08  (cost=0.00..6.00 rows=1 width=209)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 7"  (cost=0.00..5.87 rows=1 
width=209)
                           ->  Index Scan using sucks_2005_07_pkey on 
sucks_2005_07  (cost=0.00..5.86 rows=1 width=209)
                                 Index Cond: (suck_id = 7136642::numeric)
                     ->  Subquery Scan "*SELECT* 8"  (cost=0.00..5.98 rows=1 
width=212)
                           ->  Index Scan using sucks_2005_06_pkey on 
sucks_2005_06 "local"  (cost=0.00..5.97 rows=1 width=212)
                                 Index Cond: (suck_id = 7136642::numeric)
(29 rows)




can someone please tell me what we did wrong?

TIA



From pgsql-performance-owner@postgresql.org  Wed Jan 25 12:24:37 2006
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To: Richard Huxton <dev@archonet.com>
cc: Evgeny Gridasov <eugrid@fpm.kubsu.ru>, pgsql-performance@postgresql.org
Subject: Re: DB responce during DB dump 
In-reply-to: <43D772BD.8080809@archonet.com> 
References: <GJEAKHIALCNFPPGBGEKNEEBDDGAA.dan@centrifugesolutions.com>
	<20060125150134.55589806.eugrid@fpm.kubsu.ru>
	<43D772BD.8080809@archonet.com>
Comments: In-reply-to Richard Huxton <dev@archonet.com>
	message dated "Wed, 25 Jan 2006 12:44:45 +0000"
Date: Wed, 25 Jan 2006 11:21:58 -0500
Message-ID: <1459.1138206118@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Richard Huxton <dev@archonet.com> writes:
> Evgeny Gridasov wrote:
>> I've written a perl script to limit pg_dump output bandwidth,
>> ...
>> Is there any other solution to avoid this problem?

> That's an interesting solution, and I'd guess people might like to see 
> it posted to the list if it's not too big.

Years ago there was some experimentation with dump-rate throttling logic
inside pg_dump itself --- there's still a comment about it in pg_dump.c.
The experiment didn't seem very successful, which is why it never got to
be a permanent feature.  I'm curious to know why this perl script is
doing a better job than we were able to do inside pg_dump.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Wed Jan 25 12:43:12 2006
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Date: Wed, 25 Jan 2006 19:43:09 +0300
From: Evgeny Gridasov <eugrid@fpm.kubsu.ru>
To: pgsql-performance@postgresql.org
Subject: Re: DB responce during DB dump
Message-Id: <20060125194309.8cb6e5c8.eugrid@fpm.kubsu.ru>
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	<20060125150134.55589806.eugrid@fpm.kubsu.ru>
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All I was trying to achieve is to limit I/O rate done by pg_dump.
The script is a very simple pipe rate limitter and nothing more:
it reads input, but outputs data no more than at rate specified.

I guess it helps because even if pg_dump outputs data at 20 mb/sec,
the script won't be able to read it at rate higher than output rate. Pipe
buffer is not infinitive, so pg_dump output rate and hard disk reads become
almost equal the input rate of my perl script.

On Wed, 25 Jan 2006 11:21:58 -0500
Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Years ago there was some experimentation with dump-rate throttling logic
> inside pg_dump itself --- there's still a comment about it in pg_dump.c.
> The experiment didn't seem very successful, which is why it never got to
> be a permanent feature.  I'm curious to know why this perl script is
> doing a better job than we were able to do inside pg_dump.

-- 
Evgeny Gridasov
Software Engineer 
I-Free, Russia

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Date: Wed, 25 Jan 2006 19:47:27 +0300
From: Evgeny Gridasov <eugrid@fpm.kubsu.ru>
To: pgsql-performance@postgresql.org
Subject: Re: DB responce during DB dump
Message-Id: <20060125194727.685144d7.eugrid@fpm.kubsu.ru>
In-Reply-To: <43D772BD.8080809@archonet.com>
References: <GJEAKHIALCNFPPGBGEKNEEBDDGAA.dan@centrifugesolutions.com>
	<20060125150134.55589806.eugrid@fpm.kubsu.ru>
	<43D772BD.8080809@archonet.com>
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Ok, It's VERY simple =) here:
http://deepcore.i-free.ru/simple_shaper.pl

I could dump it to a spare machine, but I don't have one.
Current DB server is 2xXEON / 4GbRAM / RAID10 (4 SCSI HDD). Performance is excellent, except during backups.

I wanted to set up some kind of replication but it's useless - I don't have a spare machine now, may be in future...


On Wed, 25 Jan 2006 12:44:45 +0000
Richard Huxton <dev@archonet.com> wrote:

> 
> That's an interesting solution, and I'd guess people might like to see 
> it posted to the list if it's not too big.
> 
> Also, there's no reason you have to dump from the same machine, you can 
> do so over the network which should reduce activity a little bit.
> 
> Basically though, it sounds like you either need more disk I/O or a 
> different approach.
> 
> Have you looked into using PITR log-shipping or replication (e.g. slony) 
> to have an off-machine backup?

-- 
Evgeny Gridasov
Software Engineer 
I-Free, Russia

From pgsql-performance-owner@postgresql.org  Wed Jan 25 21:46:05 2006
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Date: Wed, 25 Jan 2006 17:46:12 -0800
From: Robert Lor <Robert.Lor@Sun.COM>
Subject: PostgreSQL Solaris packages now in beta
To: pgsql-performance@postgresql.org
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With big thanks to Josh Berkus and Devrim Gunduz, I'm happy to announce 
that Sun has just released a Solaris distribution of PostgreSQL 8.1.2  
with ready-to-install packages for both Sparc and x86.  These packages 
are currently in Beta, and we expect to FCS in 2 -3 weeks.  The 
packages, along with an install guide, are available for download at 
http://pgfoundry.org/projects/solarispackages/

We have tightly integrated PostgreSQL with Solaris in a manner similar 
to the Linux distributions available on postgresql.org. In fact, the 
directory structures are identical.  Starting with Solaris 10 Update 2, 
PostgreSQL will be distributed with every copy of Solaris, via download 
and physical media.

We welcome any and all feedback on this PostgreSQL Solaris 
distribution.   Please subscribe to the 
solarispackages-general@pgfoundry.org mailing list to give us feedback: 
http://pgfoundry.org/mail/?group_id=1000063

BTW, I'm a senior engineer at Sun Microsystems, recently working with 
the PostgreSQL community (namely Josh Berkus, Devrim Gunduz, and Gavin 
Sherry) on the Solaris Packages Project at PgFoundry,  PostgreSQL 
performance optimization on Solaris, and leveraging Solaris 10 
capabilities (e.g. DTrace) specifically for PostgreSQL.  I'll be posting 
a Solaris performance tuning guide in a few weeks.

Regards,
Robert Lor



From pgsql-performance-owner@postgresql.org  Thu Jan 26 06:06:25 2006
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Date: Thu, 26 Jan 2006 11:06:24 +0100
From: Paul Mackay <mackaypaul@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Physical column size
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Hi,

I've created a table like this :
CREATE TABLE tmp_A (
c "char",
i int4
);

And another one
CREATE TABLE tmp_B (
i int4,
ii int4
);

I then inerted a bit more than 19 million rows in each table (exactly the
same number of rows in each).

The end result is that the physical size on disk used by table tmp_A is
exactly the same as table tmp_B (as revealed by the pg_relation_size
function) ! Given that a "char" field is supposed to be 1 byte in size and =
a
int4 4 bytes, shouldn't the tmp_A use a smaller disk space ? Or is it that
any value, whatever the type, requires at least 4 bytes to be stored ?

Thanks,
Paul

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Hi,<br><br>I've created a table like this : <br>CREATE TABLE tmp_A (<br>c &=
quot;char&quot;,<br>i int4<br>);<br><br>And another one <br>CREATE TABLE tm=
p_B (<br>i int4,<br>ii int4<br>);<br><br>I then inerted a bit more than 19 =
million rows in each table (exactly the same number of rows in each).=20
<br><br>The end result is that the physical size on disk used by table tmp_=
A is exactly the same as table tmp_B (as revealed by the pg_relation_size f=
unction) ! Given that a &quot;char&quot; field is supposed to be 1 byte in =
size and a int4 4 bytes, shouldn't the tmp_A use a smaller disk space ? Or =
is it that any value, whatever the type, requires at least 4 bytes to be st=
ored ?=20
<br><br>Thanks,<br>Paul<br>

------=_Part_37670_2165376.1138269984348--

From pgsql-performance-owner@postgresql.org  Thu Jan 26 06:22:05 2006
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From: Mario Weilguni <mweilguni@sime.com>
To: pgsql-performance@postgresql.org
Subject: Re: Physical column size
Date: Thu, 26 Jan 2006 12:22:03 +0100
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Am Donnerstag, 26. Januar 2006 11:06 schrieb Paul Mackay:
> Hi,
>
> I've created a table like this :
> CREATE TABLE tmp_A (
> c "char",
> i int4
> );
>
> And another one
> CREATE TABLE tmp_B (
> i int4,
> ii int4
> );
>
> I then inerted a bit more than 19 million rows in each table (exactly the
> same number of rows in each).
>
> The end result is that the physical size on disk used by table tmp_A is
> exactly the same as table tmp_B (as revealed by the pg_relation_size
> function) ! Given that a "char" field is supposed to be 1 byte in size and
> a int4 4 bytes, shouldn't the tmp_A use a smaller disk space ? Or is it
> that any value, whatever the type, requires at least 4 bytes to be stored ?

I think this is caused by alignment.


From pgsql-performance-owner@postgresql.org  Thu Jan 26 10:56:29 2006
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Date: Thu, 26 Jan 2006 09:56:14 -0500
From: "Jignesh K. Shah" <J.K.Shah@Sun.COM>
Subject: Re: PostgreSQL Solaris packages now in beta
In-reply-to: <43D829E4.1060503@sun.com>
To: Robert Lor <Robert.Lor@Sun.COM>
Cc: pgsql-performance@postgresql.org
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For people installing PostgreSQL on Solaris with the new packaget, it  
will show a greatly improved experience to get PostgreSQL up and running 
which was quite a inhibitor in terms of "Love at First Sight". This will 
now help people familiar with Solaris have a great first impression of 
PostgreSQL  and hence lower the barrier of entry to PostgreSQL. With 
more than 3.7 million downloads of Solaris 10 already, now PostgreSQL 
have accesss to probably a 3.7 million  incremental user-base of these 
relatively "New" PostgreSQL users.


Regards,
Jignesh




Robert Lor wrote:

>
> With big thanks to Josh Berkus and Devrim Gunduz, I'm happy to 
> announce that Sun has just released a Solaris distribution of 
> PostgreSQL 8.1.2  with ready-to-install packages for both Sparc and 
> x86.  These packages are currently in Beta, and we expect to FCS in 2 
> -3 weeks.  The packages, along with an install guide, are available 
> for download at http://pgfoundry.org/projects/solarispackages/
>
> We have tightly integrated PostgreSQL with Solaris in a manner similar 
> to the Linux distributions available on postgresql.org. In fact, the 
> directory structures are identical.  Starting with Solaris 10 Update 
> 2, PostgreSQL will be distributed with every copy of Solaris, via 
> download and physical media.
>
> We welcome any and all feedback on this PostgreSQL Solaris 
> distribution.   Please subscribe to the 
> solarispackages-general@pgfoundry.org mailing list to give us 
> feedback: http://pgfoundry.org/mail/?group_id=1000063
>
> BTW, I'm a senior engineer at Sun Microsystems, recently working with 
> the PostgreSQL community (namely Josh Berkus, Devrim Gunduz, and Gavin 
> Sherry) on the Solaris Packages Project at PgFoundry,  PostgreSQL 
> performance optimization on Solaris, and leveraging Solaris 10 
> capabilities (e.g. DTrace) specifically for PostgreSQL.  I'll be 
> posting a Solaris performance tuning guide in a few weeks.
>
> Regards,
> Robert Lor
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 1: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly


From pgsql-performance-owner@postgresql.org  Thu Jan 26 11:43:17 2006
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Subject: Query optimization with X Y JOIN
Date: Thu, 26 Jan 2006 10:43:12 -0500
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Hey guys, how u been. This is quite a newbie question, but I need to ask =
it. I'm trying to wrap my mind around the syntax of join and why and =
when to use it. I understand the concept of making a query go faster by =
creating indexes, but it seems that when I want data from multiple =
tables that link together the query goes slow. The slow is typically due =
to expensive nested loops. The reason is, all my brain understands is:

select
    tablea.data
    tableb.data
    tablec.data
from
    tablea
    tableb
    tablec
where
    tablea.pri_key =3D tableb.foreign_key AND
    tableb.pri_key =3D tablec.foreign_key AND...

 From what I read, it seems you can use inner/outer right/left join on =
(bla) but when I see syntax examples I see that sometimes tables are =
omitted from the 'from' section of the query and other times, no. =
Sometimes I see that the join commands are nested and others, no and =
sometimes I see joins syntax that only applies to one table. From what I =
understand join can be used to tell the database the fast way to murge =
table data together to get results by specifiying the table that has the =
primary keys and the table that has the foreign keys.

I've read all through the postgres docs on this command and I'm still =
left lost. Can someone please explain to me in simple language how to =
use these commands or provide me with a link. I need it to live right =
now. Thanx.

    
------=_NextPart_000_005A_01C62265.4E685720
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>Hey guys, how u been. This is quite a =
newbie=20
question, but I need to ask it. I'm trying to wrap my mind around the =
syntax of=20
join and why and when to use it. I understand the concept of making a =
query go=20
faster by creating indexes, but it seems that when I want data from =
multiple=20
tables that link together the query goes slow. The slow is typically due =
to=20
expensive nested loops. The reason is, all my brain understands =
is:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>select</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; =
tablea.data</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; =
tableb.data</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; =
tablec.data</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>from</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; tablea</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; tableb</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; tablec</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>where</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; tablea.pri_key =3D=20
tableb.foreign_key AND</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; tableb.pri_key =3D=20
tablec.foreign_key AND...</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>From what I read, it seems you can use =
inner/outer=20
right/left join on (bla) but when I see syntax examples I see that =
sometimes=20
tables are omitted from the 'from' section of the query and other times, =
no.=20
Sometimes I see that the join commands are nested and others, no and =
sometimes I=20
see joins syntax that only applies to one table. From what I understand =
join can=20
be used to tell the database the fast way to murge table data together =
to get=20
results by specifiying the table that has the primary keys and the table =
that=20
has the foreign keys.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>I've read all through the postgres docs =
on this=20
command and I'm still left lost. Can someone please explain to me in =
simple=20
language how to use these commands or provide me with a link. I need it =
to live=20
right now. Thanx.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp; =
</FONT></DIV></BODY></HTML>

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From pgsql-performance-owner@postgresql.org  Thu Jan 26 11:50:28 2006
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Subject: Incorrect Total runtime Reported by Explain Analyze!?
Date: Thu, 26 Jan 2006 09:50:29 -0600
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From: "Jozsef Szalay" <jszalay@storediq.com>
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Hi All,

=20

I have seen it on occasion that the total runtime reported by explain
analyze was much higher than the actual time the query needed to
complete. The differences in my case ranged between 20-120 seconds. I'm
just curious if anyone else has experienced this and whether there is
something that I can do to convince explain analyze to report the
execution time of the query itself rather than the time of its own
execution. Engine version is 8.1.1.

=20

Thanks for the help!

=20


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<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
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font-family:Arial'>Hi All,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>I have seen it on occasion that the total runtime =
reported
by explain analyze was much higher than the actual time the query needed =
to
complete. The differences in my case ranged between 20-120 seconds. =
I&#8217;m
just curious if anyone else has experienced this and whether there is =
something
that I can do to convince explain analyze to report the execution time =
of the query
itself rather than the time of its own execution. Engine version is =
8.1.1.<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Thanks for the help!<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
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From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:17:24 2006
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Date: Thu, 26 Jan 2006 08:12:45 -0800
From: "Craig A. James" <cjames@modgraph-usa.com>
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To: pgsql-performance@postgresql.org
Subject: Re: Query optimization with X Y JOIN
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
	<005d01c6228f$3772dca0$0d310d05@fatchubby>
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First, this isn't really the right place to ask -- this forum is about performance, not SQL syntax.

Second, this isn't a question anyone can answer in a reasonable length of time.  What you're asking for usually is taught in a class on relational database theory, which is typically a semester or two in college.

If you really need a crash course, dig around on the web for terms like "SQL Tutorial".

Good luck,
Craig


J@Planeti.Biz wrote:
> Hey guys, how u been. This is quite a newbie question, but I need to ask 
> it. I'm trying to wrap my mind around the syntax of join and why and 
> when to use it. I understand the concept of making a query go faster by 
> creating indexes, but it seems that when I want data from multiple 
> tables that link together the query goes slow. The slow is typically due 
> to expensive nested loops. The reason is, all my brain understands is:
>  
> select
>     tablea.data
>     tableb.data
>     tablec.data
> from
>     tablea
>     tableb
>     tablec
> where
>     tablea.pri_key = tableb.foreign_key AND
>     tableb.pri_key = tablec.foreign_key AND...
>  
>  From what I read, it seems you can use inner/outer right/left join on 
> (bla) but when I see syntax examples I see that sometimes tables are 
> omitted from the 'from' section of the query and other times, no. 
> Sometimes I see that the join commands are nested and others, no and 
> sometimes I see joins syntax that only applies to one table. From what I 
> understand join can be used to tell the database the fast way to murge 
> table data together to get results by specifiying the table that has the 
> primary keys and the table that has the foreign keys.
>  
> I've read all through the postgres docs on this command and I'm still 
> left lost. Can someone please explain to me in simple language how to 
> use these commands or provide me with a link. I need it to live right 
> now. Thanx.
>  
>    

From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:25:18 2006
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From: J@Planeti.Biz
Message-ID: <008001c62295$156b8fc0$0d310d05@fatchubby>
To: <pgsql-performance@postgresql.org>
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
	<005d01c6228f$3772dca0$0d310d05@fatchubby>
	<43D8F4FD.4040703@modgraph-usa.com>
Subject: Re: Query optimization with X Y JOIN
Date: Thu, 26 Jan 2006 11:25:12 -0500
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If I want my database to go faster, due to X then I would think that the 
issue is about performance. I wasn't aware of a paticular constraint on X.

I have more that a rudementary understanding of what's going on here, I was 
just hoping that someone could shed some light on the basic principal of 
this JOIN command and its syntax. Most people I ask, don't give me straight 
answers and what I have already read on the web is not very helpful thus 
far.
----- Original Message ----- 
From: "Craig A. James" <cjames@modgraph-usa.com>
To: <pgsql-performance@postgresql.org>
Sent: Thursday, January 26, 2006 11:12 AM
Subject: Re: [PERFORM] Query optimization with X Y JOIN


> First, this isn't really the right place to ask -- this forum is about 
> performance, not SQL syntax.
>
> Second, this isn't a question anyone can answer in a reasonable length of 
> time.  What you're asking for usually is taught in a class on relational 
> database theory, which is typically a semester or two in college.
>
> If you really need a crash course, dig around on the web for terms like 
> "SQL Tutorial".
>
> Good luck,
> Craig
>
>
> J@Planeti.Biz wrote:
>> Hey guys, how u been. This is quite a newbie question, but I need to ask 
>> it. I'm trying to wrap my mind around the syntax of join and why and when 
>> to use it. I understand the concept of making a query go faster by 
>> creating indexes, but it seems that when I want data from multiple tables 
>> that link together the query goes slow. The slow is typically due to 
>> expensive nested loops. The reason is, all my brain understands is:
>>  select
>>     tablea.data
>>     tableb.data
>>     tablec.data
>> from
>>     tablea
>>     tableb
>>     tablec
>> where
>>     tablea.pri_key = tableb.foreign_key AND
>>     tableb.pri_key = tablec.foreign_key AND...
>>  From what I read, it seems you can use inner/outer right/left join on 
>> (bla) but when I see syntax examples I see that sometimes tables are 
>> omitted from the 'from' section of the query and other times, no. 
>> Sometimes I see that the join commands are nested and others, no and 
>> sometimes I see joins syntax that only applies to one table. From what I 
>> understand join can be used to tell the database the fast way to murge 
>> table data together to get results by specifiying the table that has the 
>> primary keys and the table that has the foreign keys.
>>  I've read all through the postgres docs on this command and I'm still 
>> left lost. Can someone please explain to me in simple language how to use 
>> these commands or provide me with a link. I need it to live right now. 
>> Thanx.
>>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 1: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly
> 


From pgsql-sql-owner@postgresql.org  Thu Jan 26 12:33:39 2006
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Date: Thu, 26 Jan 2006 11:33:34 -0500
From: Jaime Casanova <systemguards@gmail.com>
To: "J@planeti.biz" <J@planeti.biz>
Subject: Re: [PERFORM] Query optimization with X Y JOIN
Cc: pgsql-sql@postgresql.org
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	<005d01c6228f$3772dca0$0d310d05@fatchubby>
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On 1/26/06, J@planeti.biz <J@planeti.biz> wrote:
> If I want my database to go faster, due to X then I would think that the
> issue is about performance. I wasn't aware of a paticular constraint on X=
.
>
> I have more that a rudementary understanding of what's going on here, I w=
as
> just hoping that someone could shed some light on the basic principal of
> this JOIN command and its syntax. Most people I ask, don't give me straig=
ht
> answers and what I have already read on the web is not very helpful thus
> far.

http://www.postgresql.org/docs/current/static/sql-select.html

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)

From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:33:10 2006
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Subject: Re: Query optimization with X Y JOIN
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
	<005d01c6228f$3772dca0$0d310d05@fatchubby>
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J@Planeti.Biz wrote:
> If I want my database to go faster, due to X then I would think that 
> the issue is about performance. I wasn't aware of a paticular 
> constraint on X.
>
> I have more that a rudementary understanding of what's going on here, 
> I was just hoping that someone could shed some light on the basic 
> principal of this JOIN command and its syntax. Most people I ask, 
> don't give me straight answers and what I have already read on the web 
> is not very helpful thus far.
What you are looking for is here:

http://sqlzoo.net/

It is an excellent website that discusses in depth but at a tutorial 
style level how and what SQL is and how to use it. Including JOINS.

FYI, a JOIN is basically a FROM with an integrated WHERE clause. That is 
a very simplified description and isn't 100% accurate
but it is close. I strongly suggest the website I mentioned above as it 
will resolve your question.

Joshua D. Drake

-- 
The PostgreSQL Company - Command Prompt, Inc. 1.503.667.4564
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From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:35:49 2006
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Subject: Re: Incorrect Total runtime Reported by Explain Analyze!?
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Jozsef Szalay <jszalay@storediq.com>
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On Thu, 2006-01-26 at 09:50, Jozsef Szalay wrote:
> Hi All,
>=20
> =20
>=20
> I have seen it on occasion that the total runtime reported by explain
> analyze was much higher than the actual time the query needed to
> complete. The differences in my case ranged between 20-120 seconds.
> I=E2=80=99m just curious if anyone else has experienced this and whether =
there
> is something that I can do to convince explain analyze to report the
> execution time of the query itself rather than the time of its own
> execution. Engine version is 8.1.1.

I've seen this problem before in 7.4 and 8.0 as well.

From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:47:59 2006
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From: Richard Huxton <dev@archonet.com>
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To: J@Planeti.Biz
Cc: pgsql-performance@postgresql.org
Subject: Re: Query optimization with X Y JOIN
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
	<005d01c6228f$3772dca0$0d310d05@fatchubby>
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J@Planeti.Biz wrote:
> If I want my database to go faster, due to X then I would think that the 
> issue is about performance. I wasn't aware of a paticular constraint on X.

You haven't asked a performance question yet though.

> I have more that a rudementary understanding of what's going on here, I 
> was just hoping that someone could shed some light on the basic 
> principal of this JOIN command and its syntax. Most people I ask, don't 
> give me straight answers and what I have already read on the web is not 
> very helpful thus far.

OK - firstly it's not a JOIN command. It's a SELECT query that happens 
to join (in your example) three tables together. The syntax is specified 
in the SQL reference section of the manuals, and I don't think it's 
different from the standard SQL spec here.

A query that joins two or more tables (be they real base-tables, views 
or sub-query result-sets) produces the product of both. Normally you 
don't want this so you apply constraints to that join (table_a.col1 = 
table_b.col2).

In some cases you want all the rows from one side of a join, whether or 
not you get a match on the other side of the join. This is called an 
outer join and results in NULLs for all the columns on the "outside" of 
the join. A left-join returns all rows from the table on the left of the 
join, a right-join from the table on the right of it.

When planning a join, the planner will try to estimate how many matches 
it will see on each side, taking into account any extra constraints (you 
might want only some of the rows in table_a anyway). It then decides 
whether to use any indexes on the relevant column(s).

Now, if you think the planner is making a mistake we'll need to see the 
output of EXPLAIN ANALYSE for the query and will want to know that 
you've vacuumed and analysed the tables in question.

Does that help at all?
-- 
   Richard Huxton
   Archonet Ltd

From pgsql-performance-owner@postgresql.org  Thu Jan 26 12:50:05 2006
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Jozsef Szalay wrote:
> 
> I have seen it on occasion that the total runtime reported by explain
> analyze was much higher than the actual time the query needed to
> complete. The differences in my case ranged between 20-120 seconds. I'm
> just curious if anyone else has experienced this and whether there is
> something that I can do to convince explain analyze to report the
> execution time of the query itself rather than the time of its own
> execution. Engine version is 8.1.1.

I think it's down to all the gettime() calls that have to be made to 
measure how long each stage of the query takes. In some cases these can 
take a substantial part of the overall query time. I seem to recall one 
of the BSDs was particularly bad in this respect a couple of years ago. 
Does that sound like your problem?

-- 
   Richard Huxton
   Archonet Ltd

From pgsql-performance-owner@postgresql.org  Thu Jan 26 13:13:38 2006
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Subject: Re: Query optimization with X Y JOIN
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Yes, that helps a great deal. Thank you so much.

----- Original Message ----- 
From: "Richard Huxton" <dev@archonet.com>
To: <J@planeti.biz>
Cc: <pgsql-performance@postgresql.org>
Sent: Thursday, January 26, 2006 11:47 AM
Subject: Re: [PERFORM] Query optimization with X Y JOIN


> J@Planeti.Biz wrote:
>> If I want my database to go faster, due to X then I would think that the 
>> issue is about performance. I wasn't aware of a paticular constraint on 
>> X.
>
> You haven't asked a performance question yet though.
>
>> I have more that a rudementary understanding of what's going on here, I 
>> was just hoping that someone could shed some light on the basic principal 
>> of this JOIN command and its syntax. Most people I ask, don't give me 
>> straight answers and what I have already read on the web is not very 
>> helpful thus far.
>
> OK - firstly it's not a JOIN command. It's a SELECT query that happens to 
> join (in your example) three tables together. The syntax is specified in 
> the SQL reference section of the manuals, and I don't think it's different 
> from the standard SQL spec here.
>
> A query that joins two or more tables (be they real base-tables, views or 
> sub-query result-sets) produces the product of both. Normally you don't 
> want this so you apply constraints to that join (table_a.col1 = 
> table_b.col2).
>
> In some cases you want all the rows from one side of a join, whether or 
> not you get a match on the other side of the join. This is called an outer 
> join and results in NULLs for all the columns on the "outside" of the 
> join. A left-join returns all rows from the table on the left of the join, 
> a right-join from the table on the right of it.
>
> When planning a join, the planner will try to estimate how many matches it 
> will see on each side, taking into account any extra constraints (you 
> might want only some of the rows in table_a anyway). It then decides 
> whether to use any indexes on the relevant column(s).
>
> Now, if you think the planner is making a mistake we'll need to see the 
> output of EXPLAIN ANALYSE for the query and will want to know that you've 
> vacuumed and analysed the tables in question.
>
> Does that help at all?
> -- 
>   Richard Huxton
>   Archonet Ltd
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
> 


From pgsql-performance-owner@postgresql.org  Thu Jan 26 13:35:28 2006
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Subject: Re: Incorrect Total runtime Reported by Explain Analyze!?
Date: Thu, 26 Jan 2006 11:35:25 -0600
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Thread-Topic: [PERFORM] Incorrect Total runtime Reported by Explain Analyze!?
Thread-Index: AcYimI1ubX+5EvLDQkOkGDJFoW4h9QABGxTA
From: "Jozsef Szalay" <jszalay@storediq.com>
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It might be. I'm running on Fedora Linux kernel 2.6.5-1.358smp, GCC
3.3.3, glibc-2.3.3-27


-----Original Message-----
From: Richard Huxton [mailto:dev@archonet.com]=20
Sent: Thursday, January 26, 2006 10:50 AM
To: Jozsef Szalay
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Incorrect Total runtime Reported by Explain
Analyze!?

Jozsef Szalay wrote:
>=20
> I have seen it on occasion that the total runtime reported by explain
> analyze was much higher than the actual time the query needed to
> complete. The differences in my case ranged between 20-120 seconds.
I'm
> just curious if anyone else has experienced this and whether there is
> something that I can do to convince explain analyze to report the
> execution time of the query itself rather than the time of its own
> execution. Engine version is 8.1.1.

I think it's down to all the gettime() calls that have to be made to=20
measure how long each stage of the query takes. In some cases these can=20
take a substantial part of the overall query time. I seem to recall one=20
of the BSDs was particularly bad in this respect a couple of years ago.=20
Does that sound like your problem?

--=20
   Richard Huxton
   Archonet Ltd


From pgsql-performance-owner@postgresql.org  Thu Jan 26 13:57:33 2006
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Subject: Re: Incorrect Total runtime Reported by Explain Analyze!?
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On Thu, Jan 26, 2006 at 04:49:59PM +0000, Richard Huxton wrote:
> Jozsef Szalay wrote:
> >I have seen it on occasion that the total runtime reported by explain
> >analyze was much higher than the actual time the query needed to
> >complete. The differences in my case ranged between 20-120 seconds. I'm
> >just curious if anyone else has experienced this and whether there is
> >something that I can do to convince explain analyze to report the
> >execution time of the query itself rather than the time of its own
> >execution. Engine version is 8.1.1.
> 
> I think it's down to all the gettime() calls that have to be made to 
> measure how long each stage of the query takes. In some cases these can 
> take a substantial part of the overall query time.

Another possibility is that the total query time was indeed that
long because the query was blocked waiting for a lock.  For example:

T1: BEGIN;
T2: BEGIN;
T1: SELECT * FROM foo WHERE id = 1 FOR UPDATE;
T2: EXPLAIN ANALYZE UPDATE foo SET x = x + 1 WHERE id = 1;
T1: (do something for a long time)
T1: COMMIT;

When T2's EXPLAIN ANALYZE finally returns it'll show something like
this:

test=> EXPLAIN ANALYZE UPDATE foo SET x = x + 1 WHERE id = 1;
                                                  QUERY PLAN                                                   
---------------------------------------------------------------------------------------------------------------
 Index Scan using foo_pkey on foo  (cost=0.00..3.92 rows=1 width=14) (actual time=0.123..0.138 rows=1 loops=1)
   Index Cond: (id = 1)
 Total runtime: 31926.304 ms
(3 rows)

SELECT queries can be blocked by operations that take an Access
Exclusive lock, such as CLUSTER, VACUUM FULL, or REINDEX.  Have you
ever examined pg_locks during one of these queries to look for
ungranted locks?

If this weren't 8.1 I'd ask if you had any triggers (including
foreign key constraints), whose execution time EXPLAIN ANALYZE
doesn't show in earlier versions.  For example:

8.1.2:
test=> EXPLAIN ANALYZE DELETE FROM foo WHERE id = 1;
                                                  QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Index Scan using foo_pkey on foo  (cost=0.00..3.92 rows=1 width=6) (actual time=0.136..0.154 rows=1 loops=1)
   Index Cond: (id = 1)
 Trigger for constraint bar_fooid_fkey: time=1538.054 calls=1
 Total runtime: 1539.732 ms
(4 rows)

8.0.6:
test=> EXPLAIN ANALYZE DELETE FROM foo WHERE id = 1;
                                                  QUERY PLAN                                                  
--------------------------------------------------------------------------------------------------------------
 Index Scan using foo_pkey on foo  (cost=0.00..3.92 rows=1 width=6) (actual time=0.124..0.147 rows=1 loops=1)
   Index Cond: (id = 1)
 Total runtime: 1746.173 ms
(3 rows)

-- 
Michael Fuhr

From pgsql-performance-owner@postgresql.org  Thu Jan 26 13:59:52 2006
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Subject: Re: Incorrect Total runtime Reported by Explain Analyze!?
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Michael Fuhr <mike@fuhr.org>
Cc: Richard Huxton <dev@archonet.com>, Jozsef Szalay <jszalay@storediq.com>,
	pgsql-performance@postgresql.org
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On Thu, 2006-01-26 at 11:57, Michael Fuhr wrote:
> On Thu, Jan 26, 2006 at 04:49:59PM +0000, Richard Huxton wrote:
> > Jozsef Szalay wrote:
> > >I have seen it on occasion that the total runtime reported by explain
> > >analyze was much higher than the actual time the query needed to
> > >complete. The differences in my case ranged between 20-120 seconds. I'm
> > >just curious if anyone else has experienced this and whether there is
> > >something that I can do to convince explain analyze to report the
> > >execution time of the query itself rather than the time of its own
> > >execution. Engine version is 8.1.1.
> > 
> > I think it's down to all the gettime() calls that have to be made to 
> > measure how long each stage of the query takes. In some cases these can 
> > take a substantial part of the overall query time.
> 
> Another possibility is that the total query time was indeed that
> long because the query was blocked waiting for a lock.  For example:

Could be, but I've had this happen where the query returned in like 1
second but reported 30 seconds run time.

From pgsql-performance-owner@postgresql.org  Thu Jan 26 14:03:39 2006
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Subject: Re: Incorrect Total runtime Reported by Explain Analyze!?
Date: Thu, 26 Jan 2006 12:03:36 -0600
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From: "Jozsef Szalay" <jszalay@storediq.com>
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Very good points thanks. In my case however, I was doing performance
tests and therefore I had a very controlled environment with a single
client (me) doing strictly read-only multi-join queries.

-----Original Message-----
From: Michael Fuhr [mailto:mike@fuhr.org]=20
Sent: Thursday, January 26, 2006 11:57 AM
To: Richard Huxton
Cc: Jozsef Szalay; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Incorrect Total runtime Reported by Explain
Analyze!?

On Thu, Jan 26, 2006 at 04:49:59PM +0000, Richard Huxton wrote:
> Jozsef Szalay wrote:
> >I have seen it on occasion that the total runtime reported by explain
> >analyze was much higher than the actual time the query needed to
> >complete. The differences in my case ranged between 20-120 seconds.
I'm
> >just curious if anyone else has experienced this and whether there is
> >something that I can do to convince explain analyze to report the
> >execution time of the query itself rather than the time of its own
> >execution. Engine version is 8.1.1.
>=20
> I think it's down to all the gettime() calls that have to be made to=20
> measure how long each stage of the query takes. In some cases these
can=20
> take a substantial part of the overall query time.

Another possibility is that the total query time was indeed that
long because the query was blocked waiting for a lock.  For example:

T1: BEGIN;
T2: BEGIN;
T1: SELECT * FROM foo WHERE id =3D 1 FOR UPDATE;
T2: EXPLAIN ANALYZE UPDATE foo SET x =3D x + 1 WHERE id =3D 1;
T1: (do something for a long time)
T1: COMMIT;

When T2's EXPLAIN ANALYZE finally returns it'll show something like
this:

test=3D> EXPLAIN ANALYZE UPDATE foo SET x =3D x + 1 WHERE id =3D 1;
                                                  QUERY PLAN

------------------------------------------------------------------------
---------------------------------------
 Index Scan using foo_pkey on foo  (cost=3D0.00..3.92 rows=3D1 =
width=3D14)
(actual time=3D0.123..0.138 rows=3D1 loops=3D1)
   Index Cond: (id =3D 1)
 Total runtime: 31926.304 ms
(3 rows)

SELECT queries can be blocked by operations that take an Access
Exclusive lock, such as CLUSTER, VACUUM FULL, or REINDEX.  Have you
ever examined pg_locks during one of these queries to look for
ungranted locks?

If this weren't 8.1 I'd ask if you had any triggers (including
foreign key constraints), whose execution time EXPLAIN ANALYZE
doesn't show in earlier versions.  For example:

8.1.2:
test=3D> EXPLAIN ANALYZE DELETE FROM foo WHERE id =3D 1;
                                                  QUERY PLAN

------------------------------------------------------------------------
--------------------------------------
 Index Scan using foo_pkey on foo  (cost=3D0.00..3.92 rows=3D1 =
width=3D6)
(actual time=3D0.136..0.154 rows=3D1 loops=3D1)
   Index Cond: (id =3D 1)
 Trigger for constraint bar_fooid_fkey: time=3D1538.054 calls=3D1
 Total runtime: 1539.732 ms
(4 rows)

8.0.6:
test=3D> EXPLAIN ANALYZE DELETE FROM foo WHERE id =3D 1;
                                                  QUERY PLAN

------------------------------------------------------------------------
--------------------------------------
 Index Scan using foo_pkey on foo  (cost=3D0.00..3.92 rows=3D1 =
width=3D6)
(actual time=3D0.124..0.147 rows=3D1 loops=3D1)
   Index Cond: (id =3D 1)
 Total runtime: 1746.173 ms
(3 rows)

--=20
Michael Fuhr


From pgsql-performance-owner@postgresql.org  Thu Jan 26 20:18:41 2006
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Date: Thu, 26 Jan 2006 19:18:35 -0500
To: Tom Lane <tgl@sss.pgh.pa.us>,pgsql-performance@postgresql.org
From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very 
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At 01:27 PM 1/21/2006, Tom Lane wrote:
>Ron <rjpeace@earthlink.net> writes:
> > At 07:23 PM 1/20/2006, Tom Lane wrote:
> >> Well, we're trying to split an index page that's gotten full into
> >> two index pages, preferably with approximately equal numbers of items in
> >> each new page (this isn't a hard requirement though).
>
> > Maybe we are over thinking this.  What happens if we do the obvious
> > and just make a new page and move the "last" n/2 items on the full
> > page to the new page?
>
>Search performance will go to hell in a handbasket :-(.  We have to make
>at least some effort to split the page in a way that will allow searches
>to visit only one of the two child pages rather than both.
>
>It's certainly true though that finding the furthest pair is not a
>necessary component of that.  It's reasonable if you try to visualize
>the problem in 2D or 3D, but I'm not sure that that geometric intuition
>holds up in such a high-dimensional space as we have here.
After reading the various papers available on GiST and RD trees, I 
think I have a decent suggestion.

Since RD tree keys contain the keys of their descendents/components 
in them, they are basically a representation of a depth first 
search.  This can be useful for intra-document searches.

OTOH, inter-document searches are going to be more akin to breadth 
first searches using RD trees.

Thus my suggestion is that we maintain =two= index structures for text data.

The first contains as many keys and all their descendents as 
possible.  When we can no longer fit a specific complete "path" into 
a page, we start a new one; trying to keep complete top level to leaf 
key sets within a page.  This will minimize paging during 
intra-document searches.

The second index keeps siblings within a page and avoids putting 
parents or children within a page unless the entire depth first 
search can be kept within the page in addition to the siblings 
present.  This will minimize paging during inter-document searches.

Traditional B-tree ordering methods can be used to define the 
ordering/placement of pages within each index, which will minimize 
head seeks to find the correct page to scan.

Since the criteria for putting a key within a page or starting a new 
page is simple, performance for those tasks should be O(1).

The price is the extra space used for two indexes instead of one, but 
at first glance that seems well worth it.

Comments?
Ron





From pgsql-performance-owner@postgresql.org  Thu Jan 26 20:58:00 2006
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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Ron <rjpeace@earthlink.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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Ron wrote:
> At 01:27 PM 1/21/2006, Tom Lane wrote:
> >Ron <rjpeace@earthlink.net> writes:
> >> At 07:23 PM 1/20/2006, Tom Lane wrote:
> >>> Well, we're trying to split an index page that's gotten full into
> >>> two index pages, preferably with approximately equal numbers of items in
> >>> each new page (this isn't a hard requirement though).

> After reading the various papers available on GiST and RD trees, I 
> think I have a decent suggestion.

I for one don't understand what does your suggestion have to do with the
problem at hand ... not that I have a better one myself.

-- 
Alvaro Herrera                 http://www.amazon.com/gp/registry/CTMLCN8V17R4
"Siempre hay que alimentar a los dioses, aunque la tierra est� seca" (Orual)

From pgsql-performance-owner@postgresql.org  Thu Jan 26 21:55:53 2006
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From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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At 08:00 PM 1/26/2006, Alvaro Herrera wrote:
>Ron wrote:
> > At 01:27 PM 1/21/2006, Tom Lane wrote:
> > >Ron <rjpeace@earthlink.net> writes:
> > >> At 07:23 PM 1/20/2006, Tom Lane wrote:
> > >>> Well, we're trying to split an index page that's gotten full into
> > >>> two index pages, preferably with approximately equal numbers 
> of items in
> > >>> each new page (this isn't a hard requirement though).
>
> > After reading the various papers available on GiST and RD trees, I
> > think I have a decent suggestion.
>
>I for one don't understand what does your suggestion have to do with the
>problem at hand ... not that I have a better one myself.

We have two problems here.
The first is that the page splitting code for these indexes currently 
has O(N^2) performance.
The second is that whatever solution we do use for this 
functionality, we still need good performance during searches that 
use the index.  It's not clear that the solutions we've discussed to 
splitting index pages thus far will result in good performance during searches.

My suggestion is intended to address both issues.

If I'm right it helps obtain high performance during searches while 
allowing the index page splitting code to be O(1)

Ron.  



From pgsql-performance-owner@postgresql.org  Thu Jan 26 22:33:58 2006
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To: Ron <rjpeace@earthlink.net>, pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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Ron <rjpeace@earthlink.net> writes:
> We have two problems here.
> The first is that the page splitting code for these indexes currently 
> has O(N^2) performance.
> The second is that whatever solution we do use for this functionality, 
> we still need good performance during searches that use the index.

No, unfortunately that's not the problem that needs to be solved.

The problem is figuring out WHICH records to put in the "left" and "right" trees once you split them.  If you can figure that out, then your suggestion (and perhaps other techniques) could be useful.

The problem boils down to this:  You have a whole bunch of essentially random bitmaps.  You have two buckets.  You want to put half of the bitmaps in one bucket, and half in the other bucket, and when you get through, you want all of the bitmaps in each bucket to be maximally similar to each other, and maximally dissimilar to the ones in the other bucket.

That way, when you OR all the bitmaps in each bucket together to build the bitmap for the left and right child nodes of the tree, you'll get maximum separation -- the chances that you'll have to descend BOTH the left and right nodes of the tree are minimized.

Unfortunately, this problem is very likely in the set of NP-complete problems, i.e. like the famous "Traveling Salesman Problem," you can prove there's no algorithm that will give the answer in a reasonable time.  In this case, "reasonable" would be measured in milliseconds to seconds, but in fact an actual "perfect" split of a set of bitmaps probably can't be computed in the lifetime of the universe for more than a few hundred bitmaps.

That's the problem that's being discussed: How do you decide which bitmaps go in each of the two buckets?  Any solution will necessarily be imperfect, a pragmatic algorithm that gives an imperfect, but acceptable, answer.  

As I mentioned earlier, chemists make extensive use of bitmaps to categorize and group molecules.  They use Tanimoto or Tversky similarity metrics (Tanimoto is a special case of Tversky), because it's extremely fast to compare two bitmaps, and the score is highly correlated with the number of bits the two bitmaps have in common.

But even with a fast "distance" metric like Tanimoto, there's still no easy way to decide which bucket to put each bitmap into.

Craig

From pgsql-performance-owner@postgresql.org  Thu Jan 26 23:33:11 2006
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To: "Craig A. James" <cjames@modgraph-usa.com>,
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From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
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You seem to have missed my point.  I just gave a very clear 
description of how to "decide which bitmaps go in each of the two 
buckets" by reformulating the question into "decide which bitmaps go 
in each of =four= buckets".

The intent is to have two indexes, one optimized for one common class 
of searches, and the other optimized for another common class of searches.

By decomposing the optimization problem into two simpler problems, 
the hope is that we address all the issues reasonably simply while 
still getting decent performance.

Nothing is free.  The price we pay, and it is significant, is that we 
now have two indexes where before we had only one.

Ron


At 09:29 PM 1/26/2006, Craig A. James wrote:
>Ron <rjpeace@earthlink.net> writes:
>>We have two problems here.
>>The first is that the page splitting code for these indexes 
>>currently has O(N^2) performance.
>>The second is that whatever solution we do use for this 
>>functionality, we still need good performance during searches that 
>>use the index.
>
>No, unfortunately that's not the problem that needs to be solved.
>
>The problem is figuring out WHICH records to put in the "left" and 
>"right" trees once you split them.  If you can figure that out, then 
>your suggestion (and perhaps other techniques) could be useful.
>
>The problem boils down to this:  You have a whole bunch of 
>essentially random bitmaps.  You have two buckets.  You want to put 
>half of the bitmaps in one bucket, and half in the other bucket, and 
>when you get through, you want all of the bitmaps in each bucket to 
>be maximally similar to each other, and maximally dissimilar to the 
>ones in the other bucket.
>
>That way, when you OR all the bitmaps in each bucket together to 
>build the bitmap for the left and right child nodes of the tree, 
>you'll get maximum separation -- the chances that you'll have to 
>descend BOTH the left and right nodes of the tree are minimized.
>
>Unfortunately, this problem is very likely in the set of NP-complete 
>problems, i.e. like the famous "Traveling Salesman Problem," you can 
>prove there's no algorithm that will give the answer in a reasonable 
>time.  In this case, "reasonable" would be measured in milliseconds 
>to seconds, but in fact an actual "perfect" split of a set of 
>bitmaps probably can't be computed in the lifetime of the universe 
>for more than a few hundred bitmaps.
>
>That's the problem that's being discussed: How do you decide which 
>bitmaps go in each of the two buckets?  Any solution will 
>necessarily be imperfect, a pragmatic algorithm that gives an 
>imperfect, but acceptable, answer.
>
>As I mentioned earlier, chemists make extensive use of bitmaps to 
>categorize and group molecules.  They use Tanimoto or Tversky 
>similarity metrics (Tanimoto is a special case of Tversky), because 
>it's extremely fast to compare two bitmaps, and the score is highly 
>correlated with the number of bits the two bitmaps have in common.
>
>But even with a fast "distance" metric like Tanimoto, there's still 
>no easy way to decide which bucket to put each bitmap into.
>
>Craig



From pgsql-performance-owner@postgresql.org  Fri Jan 27 03:52:53 2006
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To: "Craig A. James" <cjames@modgraph-usa.com>,
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From: Ron <rjpeace@earthlink.net>
Subject: Re: [GENERAL] Creation of tsearch2 index is very
Cc: Tom Lane <tgl@sss.pgh.pa.us>
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At 11:13 PM 1/26/2006, Craig A. James wrote:
>Ron,
>
>I'll write to you privately, because these discussions can get messy 
>"in public".

I'm responding to this missive publicly in an attempt to help the 
discussion along.  It is not my usual practice to respond to private 
messages publicly, but this seems a good case for an exception.


>>You seem to have missed my point.  I just gave a very clear 
>>description of how to "decide which bitmaps go in each of the two 
>>buckets" by reformulating the question into "decide which bitmaps 
>>go in each of =four= buckets".
>
>Sorry to disagree, but here's the problem. It's not whether you put 
>them into two, or four, or N buckets.  The problem is, how do you 
>categorize them to begin with, so that you have some reasonable 
>criterion for which item goes in which bucket?  THAT is the hard 
>problem, not whether you have two or four buckets.

Agreed.  ...and I've given the answer to "how do you categorize them" 
using a general property of RD Trees which should result in "a 
reasonable criterion for which item goes in which bucket" when used 
for text searching.

The definition of RD tree keys being either "atomic" (non 
decomposable) or "molecular" (containing the keys of their 
descendents) is the one source of our current problems figuring out 
how to split them and, if I'm correct, a hint as to how to solve the 
splitting problem in O(1) time while helping to foster high 
performance during seearches.


>Earlier, you wrote:
>>Traditional B-tree ordering methods can be used to define the 
>>ordering/placement of pages within each index, which will minimize 
>>head seeks to find the correct page to scan.
>>Since the criteria for putting a key within a page or starting a 
>>new page is simple, performance for those tasks should be O(1).
>
>What are the "traditional B-tree ordering methods"?  That's the 
>issue, right there.  The problem is that bitmaps HAVE NO ORDERING 
>METHOD.  You can't sort them numerically or alphabetically.
The =bitmaps= have no ordering method.  =Pages= of bitmaps MUST have 
an ordering method or we have no idea which page to look at when 
searching for a key.

Treating the "root" bitmaps (those that may have descendents but have 
no parents) as numbers and ordering the pages using B tree creation 
methods that use those numbers as keys is a simple way to create a 
balanced data structure with high fan out.  IOW, a recipe for finding 
the proper page(s) to scan using minimal seeks.


>Take a crowd of people.  It's easy to divide them in half by names: 
>just alphabetize and split the list in half.  That's what your 
>solution would improve on.
>
>But imagine I gave you a group of people and told you to put them 
>into two rooms, such that when you are through, the people in each 
>room are maximally similar to each other and maximally dissimilar to 
>the people in the other room.  How would you do it?
>
>First of all, you'd have to define what "different" and "same" 
>are.  Is your measure based on skin color, hair color, age, height, 
>weight, girth, intelligence, speed, endurance, body odor, ... 
>?  Suppose I tell you, "All of those".  You have to sort the people 
>so that your two groups are separated such that the group 
>differences are maximized in this N-dimensional 
>space.  Computationally, it's a nearly impossible problem.
I'm =changing= the problem using the semantics of RD trees.  Using an 
RD tree representation, we'd create and assign a key for each person 
that ranked them compared to everyone else for each of the metrics we 
decided to differentiate on.

Then we start to form trees of keys to these people by creating 
"parent" keys as roots that contain the union of everyone with the 
same or possibly similar value for some quality.  By iterating this 
process, we end up with a bottom up construction method for an RD 
tree whose root key will the union of all the keys representing these 
people.  If this is one data structure, we end up with an efficient 
and effective way of answering not only Boolean but also ranking and 
similarity type queries.

The problem comes when we have to split this monolithic DS into 
pieces for best performance.  As many have noted, there is no 
simple  way to decide how to do such a thing.

OTOH, we =do= have the knowledge of how RD trees are built and what 
their keys represent, and we know that queries are going to tend 
strongly to either a) traverse the path from parent to child (depth 
first) or b) find all siblings with (dis)similar characteristics 
(breadth first), or c) contain a mixture of a) and b).

So I'm suggesting that conceptually we clone the original RD tree and 
we split each clone according to two different methods.
Method A results in pages that contain as many complete depth first 
paths from root to leave as possible on each page.
Method B results in pages that contain as many siblings as possible per page.
...and we use the appropriate index during each type of query or query part.

In return for using 2x as much space, we should have a general method 
that is O(1) for decomposing RD trees in such a way as to support 
high performance during searches.


>Here's a much simpler version of the problem.  Suppose I give you 
>1000 numbers, and tell you to divide them in half so that the two 
>groups have the smallest standard deviation within each group 
>possible, and the two average values of the groups of numbers are 
>the farthest apart possible.  Pretty easy, right?
>
>Now do it where "distance" is evaluated modulo(10), that is, 1 and 9 
>are closer together than 1 and 3.  Now try it -- you'll find that 
>this problem is almost impossible to solve.
This is orthogonal to the discussion at hand since the above is not 
akin to text searching nor best done with RD trees and that is 
exactly what this discussion is about.  We don't have to solve a 
general problem for all domains.  We only have to solve it for the 
specific domain of text search using the specific DS of RD trees.


>The problem is that, as database designers, we're used to text and 
>numbers, which have an inherent order.  Bitmaps have no ordering -- 
>you can't say one is "greater than" or "less than" the other.  All 
>you can do is determine that A and B are "more similar" or "less 
>similar" than A and C.
Text and numbers only have an order because we deem them to.  There 
is even a very common default order we tend to use.  But even in the 
trivial case of ranking we've all said that "1" is better than "2" in 
one situation and "2" is better than "1" in another.

In the case of text searching, the bitmaps represent where to find 
legomena, AKA specific tokens.  Particularly hapax legomena, AKA 
unique tokens.  Hapax Legomena are particularly important because 
they are maximally efficient at driving the search needed to answer a query.

While absolute hapax legomena are great for quickly pruning things 
within a document or document region, relative hapax legomena can do 
the same thing when searching among multiple documents or document regions.

The two indexes I'm suggesting are designed to take advantage of this 
general property of text searching.


Hopefully this clarifies things and motivates a better discussion?
Ron 



From pgsql-performance-owner@postgresql.org  Fri Jan 27 21:27:33 2006
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Does anyone have any experience with extremely large data sets?
I'm mean hundreds of millions of rows.

The queries I need to run on my 200 million transactions are relatively
simple:

   select month, count(distinct(cardnum)) count(*), sum(amount) from
transactions group by month;

This query took 18 hours on PG 8.1 on a Dual Xeon, RHEL3, (2.4 Kernel) with
RAID-10 (15K drives)
and 12 GB Ram.  I was expecting it to take about 4 hours - based on some
experience with a
similar dataset on a different machine (RH9, PG7.3 Dual Xeon, 4GB RAM,
Raid-5 10K drives)

  This machine is COMPLETELY devoted to running these relatively simple
queries one at a
time. (No multi-user support needed!)    I've been tooling with the various
performance settings:
effective_cache at 5GB, shared_buffers at 2 GB, workmem, sortmem at 1 GB
each.
( Shared buffers puzzles me a it bit - my instinct says to set it as high as
possible,
but everything I read says that "too high" can hurt performance.)

   Any ideas for performance tweaking in this kind of application would be
greatly appreciated.
We've got indexes on the fields being grouped, and always vacuum analzye
after building them.

   It's difficult to just "try" various ideas because each attempt takes a
full day to test.  Real
experience is needed here!

Thanks much,

Mike


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Date: Fri, 27 Jan 2006 19:05:04 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Mike Biamonte" <mike@dbeat.com>,
	pgsql-performance@postgresql.org
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--B_3221286835_1192920
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Sounds like you are running into the limits of your disk subsystem.  You ar=
e
scanning all of the data in the transactions table, so you will be limited
by the disk bandwidth you have =AD and using RAID-10, you should divide the
number of disk drives by 2 and multiply by their indiividual bandwidth
(around 60MB/s) and that=B9s what you can expect in terms of performance.  So=
,
if you have 8 drives, you should expect to get 4 x 60 MB/s =3D 240 MB/s in
bandwidth.  That means that if you are dealing with 24,000 MB of data in th=
e
=B3transactions=B2 table, then you will scan  it in 100 seconds.

With a workload like this, you are in the realm of business intelligence /
data warehousing I think.  You should check your disk performance, I would
expect you=B9ll find it lacking, partly because you are running RAID10, but
mostly because I expect you are using a hardware RAID adapter.

- Luke


On 1/27/06 5:23 PM, "Mike Biamonte" <mike@dbeat.com> wrote:

>=20
>=20
>=20
> Does anyone have any experience with extremely large data sets?
> I'm mean hundreds of millions of rows.
>=20
> The queries I need to run on my 200 million transactions are relatively
> simple:
>=20
>    select month, count(distinct(cardnum)) count(*), sum(amount) from
> transactions group by month;
>=20
> This query took 18 hours on PG 8.1 on a Dual Xeon, RHEL3, (2.4 Kernel) wi=
th
> RAID-10 (15K drives)
> and 12 GB Ram.  I was expecting it to take about 4 hours - based on some
> experience with a
> similar dataset on a different machine (RH9, PG7.3 Dual Xeon, 4GB RAM,
> Raid-5 10K drives)
>=20
>   This machine is COMPLETELY devoted to running these relatively simple
> queries one at a
> time. (No multi-user support needed!)    I've been tooling with the vario=
us
> performance settings:
> effective_cache at 5GB, shared_buffers at 2 GB, workmem, sortmem at 1 GB
> each.
> ( Shared buffers puzzles me a it bit - my instinct says to set it as high=
 as
> possible,
> but everything I read says that "too high" can hurt performance.)
>=20
>    Any ideas for performance tweaking in this kind of application would b=
e
> greatly appreciated.
> We've got indexes on the fields being grouped, and always vacuum analzye
> after building them.
>=20
>    It's difficult to just "try" various ideas because each attempt takes =
a
> full day to test.  Real
> experience is needed here!
>=20
> Thanks much,
>=20
> Mike
>=20
>=20
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
>=20
>=20



--B_3221286835_1192920
Content-Type: text/html;
 charset=iso-8859-1
Content-Transfer-Encoding: quoted-printable

<HTML>
<HEAD>
<TITLE>Re: [PERFORM] Huge Data sets, simple queries</TITLE>
</HEAD>
<BODY>
<FONT FACE=3D"Verdana, Helvetica, Arial"><SPAN STYLE=3D'font-size:14.0px'>Sound=
s like you are running into the limits of your disk subsystem. &nbsp;You are=
 scanning all of the data in the transactions table, so you will be limited =
by the disk bandwidth you have &#8211; and using RAID-10, you should divide =
the number of disk drives by 2 and multiply by their indiividual bandwidth (=
around 60MB/s) and that&#8217;s what you can expect in terms of performance.=
 &nbsp;So, if you have 8 drives, you should expect to get 4 x 60 MB/s =3D 240 =
MB/s in bandwidth. &nbsp;That means that if you are dealing with 24,000 MB o=
f data in the &#8220;transactions&#8221; table, then you will scan &nbsp;it =
in 100 seconds.<BR>
<BR>
With a workload like this, you are in the realm of business intelligence / =
data warehousing I think. &nbsp;You should check your disk performance, I wo=
uld expect you&#8217;ll find it lacking, partly because you are running RAID=
10, but mostly because I expect you are using a hardware RAID adapter.<BR>
<BR>
- Luke<BR>
<BR>
<BR>
On 1/27/06 5:23 PM, &quot;Mike Biamonte&quot; &lt;mike@dbeat.com&gt; wrote:=
<BR>
<BR>
</SPAN></FONT><BLOCKQUOTE><FONT FACE=3D"Verdana, Helvetica, Arial"><SPAN STYL=
E=3D'font-size:14.0px'><BR>
<BR>
<BR>
Does anyone have any experience with extremely large data sets?<BR>
I'm mean hundreds of millions of rows.<BR>
<BR>
The queries I need to run on my 200 million transactions are relatively<BR>
simple:<BR>
<BR>
&nbsp;&nbsp;&nbsp;select month, count(distinct(cardnum)) count(*), sum(amou=
nt) from<BR>
transactions group by month;<BR>
<BR>
This query took 18 hours on PG 8.1 on a Dual Xeon, RHEL3, (2.4 Kernel) with=
<BR>
RAID-10 (15K drives)<BR>
and 12 GB Ram. &nbsp;I was expecting it to take about 4 hours - based on so=
me<BR>
experience with a<BR>
similar dataset on a different machine (RH9, PG7.3 Dual Xeon, 4GB RAM,<BR>
Raid-5 10K drives)<BR>
<BR>
&nbsp;&nbsp;This machine is COMPLETELY devoted to running these relatively =
simple<BR>
queries one at a<BR>
time. (No multi-user support needed!) &nbsp;&nbsp;&nbsp;I've been tooling w=
ith the various<BR>
performance settings:<BR>
effective_cache at 5GB, shared_buffers at 2 GB, workmem, sortmem at 1 GB<BR=
>
each.<BR>
( Shared buffers puzzles me a it bit - my instinct says to set it as high a=
s<BR>
possible,<BR>
but everything I read says that &quot;too high&quot; can hurt performance.)=
<BR>
<BR>
&nbsp;&nbsp;&nbsp;Any ideas for performance tweaking in this kind of applic=
ation would be<BR>
greatly appreciated.<BR>
We've got indexes on the fields being grouped, and always vacuum analzye<BR=
>
after building them.<BR>
<BR>
&nbsp;&nbsp;&nbsp;It's difficult to just &quot;try&quot; various ideas beca=
use each attempt takes a<BR>
full day to test. &nbsp;Real<BR>
experience is needed here!<BR>
<BR>
Thanks much,<BR>
<BR>
Mike<BR>
<BR>
<BR>
---------------------------(end of broadcast)---------------------------<BR=
>
TIP 5: don't forget to increase your free space map settings<BR>
<BR>
<BR>
</SPAN></FONT></BLOCKQUOTE><FONT FACE=3D"Verdana, Helvetica, Arial"><SPAN STY=
LE=3D'font-size:14.0px'><BR>
</SPAN></FONT>
</BODY>
</HTML>


--B_3221286835_1192920--


From pgsql-performance-owner@postgresql.org  Sat Jan 28 02:56:46 2006
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Subject: Re: Huge Data sets, simple queries
From: "Jeffrey W. Baker" <jwbaker@acm.org>
To: Mike Biamonte <mike@dbeat.com>
Cc: pgsql-performance@postgresql.org
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On Fri, 2006-01-27 at 20:23 -0500, Mike Biamonte wrote:
> 
> Does anyone have any experience with extremely large data sets?
> I'm mean hundreds of millions of rows.

Sure, I think more than a few of us do.  Just today I built a summary
table from a 25GB primary table with ~430 million rows.  This took about
45 minutes.

> The queries I need to run on my 200 million transactions are relatively
> simple:
> 
>    select month, count(distinct(cardnum)) count(*), sum(amount) from
> transactions group by month;
> 
> This query took 18 hours on PG 8.1 on a Dual Xeon, RHEL3, (2.4 Kernel) with
> RAID-10 (15K drives)
> and 12 GB Ram.  I was expecting it to take about 4 hours - based on some
> experience with a
> similar dataset on a different machine (RH9, PG7.3 Dual Xeon, 4GB RAM,
> Raid-5 10K drives)

Possibly the latter machine has a faster I/O subsystem.  How large is
the table on disk?

>   This machine is COMPLETELY devoted to running these relatively simple
> queries one at a
> time. (No multi-user support needed!)    I've been tooling with the various
> performance settings:
> effective_cache at 5GB, shared_buffers at 2 GB, workmem, sortmem at 1 GB
> each.
> ( Shared buffers puzzles me a it bit - my instinct says to set it as high as
> possible,
> but everything I read says that "too high" can hurt performance.)
> 
>    Any ideas for performance tweaking in this kind of application would be
> greatly appreciated.
> We've got indexes on the fields being grouped, 
> and always vacuum analzye
> after building them.

Probably vacuum makes no difference.

>    It's difficult to just "try" various ideas because each attempt takes a
> full day to test.  Real
> experience is needed here!

Can you send us an EXPLAIN of the query?  I believe what you're seeing
here is probably:

Aggregate
+-Sort
  +-Sequential Scan

or perhaps:

Aggregate
+-Index Scan

I have a feeling that the latter will be much faster.  If your table has
been created over time, then it is probably naturally ordered by date,
and therefore also ordered by month.  You might expect a Sequential Scan
to be the fastest, but the Sort step will be a killer.  On the other
hand, if your table is badly disordered by date, the Index Scan could
also be very slow.

Anyway, send us the query plan and also perhaps a sample of vmstat
during the query.

For what it's worth, I have:

effective_cache_size            | 700000
cpu_tuple_cost                  | 0.01
cpu_index_tuple_cost            | 0.001
random_page_cost                | 3
shared_buffers                  | 50000
temp_buffers                    | 1000
work_mem                        | 1048576 <= for this query only

And here's a few lines from vmstat during the query:

procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 2  1     76  43476  94916 7655148    0    0 78800     0 1662   788 68 12  0 20
 1  1     76  45060  91196 7658088    0    0 78028     0 1639   712 71 11  0 19
 2  0     76  44668  87624 7662960    0    0 78924    52 1650   736 69 12  0 19
 2  0     76  45300  83672 7667432    0    0 83536    16 1688   768 71 12  0 18
 1  1     76  45744  80652 7670712    0    0 84052     0 1691   796 70 12  0 17

That's about 80MB/sec sequential input, for comparison purposes.

-jwb


From pgsql-performance-owner@postgresql.org  Sat Jan 28 11:55:03 2006
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To: "Mike Biamonte" <mike@dbeat.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries 
In-reply-to: <007101c623a9$82207c10$0200a8c0@videobox> 
References: <007101c623a9$82207c10$0200a8c0@videobox>
Comments: In-reply-to "Mike Biamonte" <mike@dbeat.com>
	message dated "Fri, 27 Jan 2006 20:23:55 -0500"
Date: Sat, 28 Jan 2006 10:55:02 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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"Mike Biamonte" <mike@dbeat.com> writes:
> The queries I need to run on my 200 million transactions are relatively
> simple:

>    select month, count(distinct(cardnum)) count(*), sum(amount) from
> transactions group by month;

count(distinct) is not "relatively simple", and the current
implementation isn't especially efficient.  Can you avoid that
construct?

Assuming that "month" means what it sounds like, the above would result
in running twelve parallel sort/uniq operations, one for each month
grouping, to eliminate duplicates before counting.  You've got sortmem
set high enough to blow out RAM in that scenario ...

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 28 13:08:57 2006
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Subject: Re: Huge Data sets, simple queries
From: "Jeffrey W. Baker" <jwbaker@acm.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
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On Sat, 2006-01-28 at 10:55 -0500, Tom Lane wrote:
> 
> Assuming that "month" means what it sounds like, the above would
> result
> in running twelve parallel sort/uniq operations, one for each month
> grouping, to eliminate duplicates before counting.  You've got sortmem
> set high enough to blow out RAM in that scenario ...

Hrmm, why is it that with a similar query I get a far simpler plan than
you describe, and relatively snappy runtime?

  select date
       , count(1) as nads
       , sum(case when premium then 1 else 0 end) as npremium
       , count(distinct(keyword)) as nwords
       , count(distinct(advertiser)) as nadvertisers 
    from data 
group by date 
order by date asc

                                          QUERY PLAN                                           
-----------------------------------------------------------------------------------------------
 GroupAggregate  (cost=0.00..14452743.09 rows=721 width=13)
   ->  Index Scan using data_date_idx on data  (cost=0.00..9075144.27 rows=430206752 width=13)
(2 rows)

=# show server_version;
 server_version 
----------------
 8.1.2
(1 row)

-jwb


From pgsql-performance-owner@postgresql.org  Sat Jan 28 13:37:07 2006
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To: "Jeffrey W. Baker" <jwbaker@acm.org>
cc: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries 
In-reply-to: <1138468133.9336.5.camel@noodles> 
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	message dated "Sat, 28 Jan 2006 09:08:53 -0800"
Date: Sat, 28 Jan 2006 12:37:00 -0500
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"Jeffrey W. Baker" <jwbaker@acm.org> writes:
> On Sat, 2006-01-28 at 10:55 -0500, Tom Lane wrote:
>> Assuming that "month" means what it sounds like, the above would result
>> in running twelve parallel sort/uniq operations, one for each month
>> grouping, to eliminate duplicates before counting.  You've got sortmem
>> set high enough to blow out RAM in that scenario ...

> Hrmm, why is it that with a similar query I get a far simpler plan than
> you describe, and relatively snappy runtime?

You can't see the sort operations in the plan, because they're invoked
implicitly by the GroupAggregate node.  But they're there.

Also, a plan involving GroupAggregate is going to run the "distinct"
sorts sequentially, because it's dealing with only one grouping value at
a time.  In the original case, the planner probably realizes there are
only 12 groups and therefore prefers a HashAggregate, which will try
to run all the sorts in parallel.  Your "group by date" isn't a good
approximation of the original conditions because there will be a lot
more groups.

(We might need to tweak the planner to discourage selecting
HashAggregate in the presence of DISTINCT aggregates --- I don't
remember whether it accounts for the sortmem usage in deciding
whether the hash will fit in memory or not ...)

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sat Jan 28 14:55:13 2006
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To: "Jeffrey W. Baker" <jwbaker@acm.org>, pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries 
In-reply-to: <18415.1138469820@sss.pgh.pa.us> 
References: <007101c623a9$82207c10$0200a8c0@videobox>
	<11814.1138463702@sss.pgh.pa.us> <1138468133.9336.5.camel@noodles>
	<18415.1138469820@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Sat, 28 Jan 2006 12:37:00 -0500"
Date: Sat, 28 Jan 2006 13:55:08 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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I wrote:
> (We might need to tweak the planner to discourage selecting
> HashAggregate in the presence of DISTINCT aggregates --- I don't
> remember whether it accounts for the sortmem usage in deciding
> whether the hash will fit in memory or not ...)

Ah, I take that all back after checking the code: we don't use
HashAggregate at all when there are DISTINCT aggregates, precisely
because of this memory-blow-out problem.

For both your group-by-date query and the original group-by-month query,
the plan of attack is going to be to read the original input in grouping
order (either via sort or indexscan, with sorting probably preferred
unless the table is pretty well correlated with the index) and then
sort/uniq on the DISTINCT value within each group.  The OP is probably
losing on that step compared to your test because it's over much larger
groups than yours, forcing some spill to disk.  And most likely he's not
got an index on month, so the first sort is in fact a sort and not an
indexscan.

Bottom line is that he's probably doing a ton of on-disk sorting
where you're not doing any.  This makes me think Luke's theory about
inadequate disk horsepower may be on the money.

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Sun Jan 29 07:25:26 2006
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Date: Sun, 29 Jan 2006 12:25:23 +0100
From: hubert depesz lubaczewski <depesz@gmail.com>
To: Luke Lonergan <llonergan@greenplum.com>
Subject: Re: Huge Data sets, simple queries
Cc: pgsql-performance@postgresql.org
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On 1/28/06, Luke Lonergan <llonergan@greenplum.com> wrote:
> You should check your disk performance, I would
> expect you'll find it lacking, partly because you are running RAID10, but
> mostly because I expect you are using a hardware RAID adapter.

hmm .. do i understand correctly that you're suggesting that using
raid 10 and/or hardware raid adapter might hurt disc subsystem
performance? could you elaborate on the reasons, please? it's not that
i'm against the idea - i'm just curious as this is very
"against-common-sense". and i always found it interesting when
somebody states something that uncommon...

best regards

depesz

From pgsql-performance-owner@postgresql.org  Sun Jan 29 11:43:25 2006
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From: Michael Stone <mstone+postgres@mathom.us>
Subject: Re: Huge Data sets, simple queries
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On Sun, Jan 29, 2006 at 12:25:23PM +0100, hubert depesz lubaczewski wrote:
>hmm .. do i understand correctly that you're suggesting that using
>raid 10 and/or hardware raid adapter might hurt disc subsystem
>performance? could you elaborate on the reasons, please?

I think it's been fairly well beaten to death that the low-end hardware 
raid adapters have lousy performance. It's not until you get into the 
range of battery-backed disk caches with 512M+ and multiple I/O channels 
that hardware raid becomes competitive with software raid.

Mike Stone

From pgsql-performance-owner@postgresql.org  Sun Jan 29 14:46:41 2006
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From: "Luke Lonergan" <LLonergan@greenplum.com>
To: "hubert depesz lubaczewski" <depesz@gmail.com>
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Depesz,

> [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of=20
> hubert depesz lubaczewski
> Sent: Sunday, January 29, 2006 3:25 AM
>
> hmm .. do i understand correctly that you're suggesting that=20
> using raid 10 and/or hardware raid adapter might hurt disc=20
> subsystem performance? could you elaborate on the reasons,=20
> please? it's not that i'm against the idea - i'm just curious=20
> as this is very "against-common-sense". and i always found it=20
> interesting when somebody states something that uncommon...

See previous postings on this list - often when someone is reporting a
performance problem with large data, the answer comes back that their
I/O setup is not performing well.  Most times, people are trusting that
when they buy a hardware RAID adapter and set it up, that the
performance will be what they expect and what is theoretically correct
for the number of disk drives.

In fact, in our testing of various host-based SCSI RAID adapters (LSI,
Dell PERC, Adaptec, HP SmartArray), we find that *all* of them
underperform, most of them severely.  Some produce results slower than a
single disk drive.  We've found that some external SCSI RAID adapters,
those built into the disk chassis, often perform better.  I think this
might be due to the better drivers and perhaps a different marketplace
for the higher end solutions driving performance validation.

The important lesson we've learned is to always test the I/O subsystem
performance - you can do so with a simple test like:
  time bash -c "dd if=3D/dev/zero of=3Dbigfile bs=3D8k count=3D4000000 =
&& sync"
  time dd if=3Dbigfile of=3D/dev/null bs=3D8k

If the answer isn't something close to the theoretical rate, you are
likely limited by your RAID setup.  You might be shocked to find a
severe performance problem.  If either is true, switching to software
RAID using a simple SCSI adapter will fix the problem.

BTW - we've had very good experiences with the host-based SATA adapters
from 3Ware.  The Areca controllers are also respected.

Oh - and about RAID 10 - for large data work it's more often a waste of
disk performance-wise compared to RAID 5 these days.  RAID5 will almost
double the performance on a reasonable number of drives.

- Luke


From pgsql-performance-owner@postgresql.org  Sun Jan 29 17:04:03 2006
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Subject: Re: Huge Data sets, simple queries
From: "Jeffrey W. Baker" <jwbaker@acm.org>
To: Luke Lonergan <LLonergan@greenplum.com>
Cc: pgsql-performance@postgresql.org
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On Sun, 2006-01-29 at 13:44 -0500, Luke Lonergan wrote:
> Depesz,
> 
> > [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of 
> > hubert depesz lubaczewski
> > Sent: Sunday, January 29, 2006 3:25 AM
> >
> > hmm .. do i understand correctly that you're suggesting that 
> > using raid 10 and/or hardware raid adapter might hurt disc 
> > subsystem performance? could you elaborate on the reasons, 
> > please? it's not that i'm against the idea - i'm just curious 
> > as this is very "against-common-sense". and i always found it 
> > interesting when somebody states something that uncommon...

> Oh - and about RAID 10 - for large data work it's more often a waste of
> disk performance-wise compared to RAID 5 these days.  RAID5 will almost
> double the performance on a reasonable number of drives.

I think you might want to be more specific here.  I would agree with you
for data warehousing, decision support, data mining, and similar
read-mostly non-transactional loads.  For transactional loads RAID-5 is,
generally speaking, a disaster due to the read-before-write problem.

While we're on the topic, I just installed another one of those Areca
ARC-1130 controllers with 1GB cache.  It's ludicrously fast: 250MB/sec
burst writes, CPU-limited reads.  I can't recommend them highly enough.

-jwb

PS: Could you look into fixing your mailer?  Your messages sometimes
don't contain In-Reply-To headers, and therefore don't thread properly.


From pgsql-performance-owner@postgresql.org  Sun Jan 29 20:32:18 2006
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Date: Sun, 29 Jan 2006 19:32:15 -0500
From: Michael Adler <adler@pobox.com>
To: Mike Biamonte <mike@dbeat.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
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On Fri, Jan 27, 2006 at 08:23:55PM -0500, Mike Biamonte wrote:

> This query took 18 hours on PG 8.1 on a Dual Xeon, RHEL3, (2.4
> Kernel) with RAID-10 (15K drives) and 12 GB Ram.  I was expecting it
> to take about 4 hours - based on some experience with a similar
> dataset on a different machine (RH9, PG7.3 Dual Xeon, 4GB RAM,
> Raid-5 10K drives)
>
>    It's difficult to just "try" various ideas because each attempt
> takes a full day to test.  Real experience is needed here!

It seems like you are changing multiple variables at the same time.

I think you need to first compare the query plans with EXPLAIN SELECT
to see if they are significantly different. Your upgrade from 7.3 to
8.1 may have resulted in a less optimal plan.

Second, you should monitor your IO performance during the query
execution and test it independent of postgres. Then compare the stats
between the two systems. 

As a side note, if you have many disks and you are concerned about
bottlenecks on read operations, RAID 5 may perform better than
RAID 10. 

 -Mike

From pgsql-performance-owner@postgresql.org  Sun Jan 29 23:24:26 2006
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Date: Sun, 29 Jan 2006 19:19:46 -0800
From: "Craig A. James" <cjames@modgraph-usa.com>
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To: Mike Biamonte <mike@dbeat.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
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Mike Biamonte wrote:
> Does anyone have any experience with extremely large data sets?
> I'm mean hundreds of millions of rows.
> 
> The queries I need to run on my 200 million transactions are relatively
> simple:
> 
>    select month, count(distinct(cardnum)) count(*), sum(amount) from
> transactions group by month;

This may be heretical to post to a relational-database group, but sometimes a problem can be better solved OUTSIDE of the relational system.

I had a similar problem recently: I have a set of about 100,000 distinct values, each of which occurs one to several million times in the database, with an aggregate total of several hundred million occurances in the database.

Sorting this into distinct lists ("Which rows contain this value?") proved quite time consuming (just like your case), but on reflection, I realized that it was dumb to expect a general-purpose sorting algorithm to sort a list about which I had specialized knowledge.  General-purpose sorting usually takes O(N*log(N)), but if you have a small number of distinct values, you can use "bucket sorting" and sort in O(N) time, a huge improvement.  In my case, it was even more specialized -- there was a very small number of the lists that contained thousands or millions of items, but about 95% of the lists only had a few items.

Armed with this knowledge, it took me couple weeks to write a highly-specialized sorting system that used a combination of Postgres, in-memory and disk caching, and algorithms dredged up from Knuth.  The final result ran in about four hours.

The thing to remember about relational databases is that the designers are constrained by the need for generality, reliability and SQL standards.  Given any particular well-defined task where you have specialized knowledge about the data, and/or you don't care about transactional correctness, and/or you're not concerned about data loss, a good programmer can always write a faster solution.

Of course, there's a huge penalty.  You lose support, lose of generality, the application takes on complexity that should be in the database, and on and on.  A hand-crafted solution should be avoided unless there's simply no other way.

A relational database is a tool.  Although powerful, like any tool it has limitations.  Use the tool where it's useful, and use other tools when necessary.

Craig

From pgsql-performance-owner@postgresql.org  Sun Jan 29 23:50:56 2006
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To: Jen Sale <js@slipt.net>
cc: pgsql-performance@postgresql.org
Subject: Re: Desperate: View not using indexes (very slow) 
In-reply-to: <200601251109.25876.js@slipt.net> 
References: <200601251109.25876.js@slipt.net>
Comments: In-reply-to Jen Sale <js@slipt.net>
	message dated "Wed, 25 Jan 2006 11:09:25 -0500"
Date: Sun, 29 Jan 2006 22:50:58 -0500
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Jen Sale <js@slipt.net> writes:
> can someone please tell me what we did wrong?

Joins against union subqueries aren't handled very well at the moment.
(As it happens, I'm working on that exact problem right now for 8.2,
but that won't help you today.)

The plan indicates that you are using UNION rather than UNION ALL,
which is not helping any.  Do you really need duplicate elimination
in that view?

			regards, tom lane

From pgsql-performance-owner@postgresql.org  Mon Jan 30 01:35:13 2006
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Subject: Re: Huge Data sets, simple queries
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On Sun, 29 Jan 2006, Luke Lonergan wrote:

> In fact, in our testing of various host-based SCSI RAID adapters (LSI,
> Dell PERC, Adaptec, HP SmartArray), we find that *all* of them
> underperform, most of them severely.

[snip]

> The important lesson we've learned is to always test the I/O subsystem
> performance - you can do so with a simple test like:
>  time bash -c "dd if=/dev/zero of=bigfile bs=8k count=4000000 && sync"
>  time dd if=bigfile of=/dev/null bs=8k

I'm curious about this since we're shopping around for something new...  I 
do want to get some kind of baseline to compare new products to.  Areca 
sent me stats on their SCSI->SATA controller and it looks like it maxes 
out around 10,000 IOPS.

I'd like to see how our existing stuff compares to this.  I'd especially 
like to see it in graph form such as the docs Areca sent (IOPS on one 
axis, block size on the other, etc.).  Looking at the venerable Bonnie, it 
doesn't really seem to focus so much on the number of read/write 
operations per second, but on big bulky transfers.

What are you folks using to measure your arrays?

I've been considering using some of our data and just basically 
benchmarking postgres on various hardware with that, but I cannot compare 
that to any manufacturer tests.

Sorry to meander a bit off topic, but I've been getting frustrated with 
this little endeavour...

Thanks,

Charles

> - Luke
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: Have you checked our extensive FAQ?
>
>               http://www.postgresql.org/docs/faq
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From pgsql-performance-owner@postgresql.org  Mon Jan 30 03:25:33 2006
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Date: Sun, 29 Jan 2006 23:25:22 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Charles Sprickman" <spork@bway.net>
cc: "hubert depesz lubaczewski" <depesz@gmail.com>,
	pgsql-performance@postgresql.org
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Charles,

On 1/29/06 9:35 PM, "Charles Sprickman" <spork@bway.net> wrote:

> What are you folks using to measure your arrays?

Bonnie++ measures random I/Os, numbers we find are typically in the 500/s
range, the best I've seen is 1500/s on a large Fibre Channel RAID0 (at
http://www.wlug.org.nz/HarddiskBenchmarks).

- Luke 



From pgsql-performance-owner@postgresql.org  Mon Jan 30 20:36:13 2006
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Arnau Rebassa Villalonga wrote:
> 
>   The configuration of postgresql is the default, I tried to tune the
> postgresql.conf and the results where disappointing, so I left again the
> default values.

That's the first thing to fix. Go to the page below and read through the 
  "Performance Tuning" article.
http://www.varlena.com/varlena/GeneralBits/Tidbits/index.php

-- 
   Richard Huxton
   Archonet Ltd

From pgsql-performance-owner@postgresql.org  Mon Jan 30 07:00:57 2006
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From: Michael Stone <mstone+postgres@mathom.us>
Subject: Re: Where is my bottleneck?
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On Tue, Jan 24, 2006 at 07:40:22PM +0100, Arnau Rebassa Villalonga wrote:
>   I have a performance problem and I don't know where is my bottleneck.
[snip]
>   Most of the time the idle value is even higher than 60%.

It's generally a fairly safe bet that if you are running slow and your 
cpu is idle, your i/o isn't fast enough.

Mike Stone

From pgsql-performance-owner@postgresql.org  Mon Jan 30 12:58:08 2006
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Date: Mon, 30 Jan 2006 08:49:04 -0800
Subject: Re: Where is my bottleneck?
From: "Luke Lonergan" <llonergan@greenplum.com>
To: arnaulist@andromeiberica.com,
	pgsql-performance@postgresql.org
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Arnau,

On 1/24/06 10:40 AM, "Arnau Rebassa Villalonga" <arebassa@androme.es> wrote:

> I know it's a  problem with a very big scope, but could you give me a
> hint about where I should look to?

Try this:

  time bash -c "dd if=/dev/zero of=bigfile bs=8k count=2000000 && sync"
  time dd if=bigfile of=/dev/null bs=8k

And report the results back here.  If it takes too long to complete (more
than a couple of minutes), bring up another window and run "vmstat 1" then
report the values in the columns "bi" and "bo".

- Luke



From pgsql-performance-owner@postgresql.org  Mon Jan 30 13:53:35 2006
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Date: Mon, 30 Jan 2006 18:53:29 +0100
From: hubert depesz lubaczewski <depesz@gmail.com>
To: Luke Lonergan <LLonergan@greenplum.com>
Subject: Re: Huge Data sets, simple queries
Cc: pgsql-performance@postgresql.org
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On 1/29/06, Luke Lonergan <LLonergan@greenplum.com> wrote:
> Oh - and about RAID 10 - for large data work it's more often a waste of
> disk performance-wise compared to RAID 5 these days.  RAID5 will almost
> double the performance on a reasonable number of drives.

how many is reasonable?

depesz

From pgsql-performance-owner@postgresql.org  Mon Jan 30 15:49:16 2006
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Date: Mon, 30 Jan 2006 11:48:49 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "hubert depesz lubaczewski" <depesz@gmail.com>
cc: pgsql-performance@postgresql.org
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Depesz,

On 1/30/06 9:53 AM, "hubert depesz lubaczewski" <depesz@gmail.com> wrote:

>> double the performance on a reasonable number of drives.
> 
> how many is reasonable?

What I mean by that is: given a set of disks N, the read performance of RAID
will be equal to the drive read rate A times the number of drives used for
reading by the RAID algorithm.  In the case of RAID5, that number is (N-1),
so the read rate is A x (N-1).  In the case of RAID10, that number is N/2,
so the read rate is A x (N/2). So, the ratio of read performance
RAID5/RAID10 is (N-1)/(N/2) = 2 x (N-1)/N.  For numbers of drives, this
ratio looks like this:
N       RAID5/RAID10
3       1.33  
6       1.67  
8       1.75  
14      1.86

So - I think reasonable would be 6-8, which are common disk configurations.

- Luke



From pgsql-performance-owner@postgresql.org  Mon Jan 30 16:10:42 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: arnaulist@andromeiberica.com
Cc: pgsql-performance@postgresql.org
Subject: Re: Where is my bottleneck?
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On Tue, Jan 24, 2006 at 07:40:22PM +0100, Arnau Rebassa Villalonga wrote:
> Hi all,
> 
>   I have a performance problem and I don't know where is my bottleneck.
> I have postgresql 7.4.2 running on a debian server with kernel

You should really upgrade to the latest 7.4 version. You're probably
vulnerable to some data-loss issues.

> 2.4.26-1-686-smp with two Xeon(TM) at 2.80GHz and 4GB of RAM and a RAID
> 5 made with SCSI disks. Maybe its not the latest hardware but I think

Generally speaking, databases (or anything else that does a lot of
random writes) don't like RAID5.

>   My problem is that the general performance is not good enough and I
> don't know where is the bottleneck. It could be because the queries are
> not optimized as they should be, but I also think it can be a postgresql
> configuration problem or hardware problem (HDs not beeing fast enough,
> not enough RAM, ... )

What kind of performance are you expecting? What are you actually
seeing?

>   The configuration of postgresql is the default, I tried to tune the
> postgresql.conf and the results where disappointing, so I left again the
> default values.

Probably not so good... you'll most likely want to tune shared_buffers,
sort_mem and effective_cache_size at a minimum. Granted, that might not
be your current bottleneck, but it would probably be your next.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Mon Jan 30 16:25:26 2006
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To: Luke Lonergan <llonergan@greenplum.com>
Cc: Mike Biamonte <mike@dbeat.com>, pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
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On Fri, Jan 27, 2006 at 07:05:04PM -0800, Luke Lonergan wrote:
> Sounds like you are running into the limits of your disk subsystem.  You are
> scanning all of the data in the transactions table, so you will be limited
> by the disk bandwidth you have ? and using RAID-10, you should divide the
> number of disk drives by 2 and multiply by their indiividual bandwidth
> (around 60MB/s) and that?s what you can expect in terms of performance.  So,
> if you have 8 drives, you should expect to get 4 x 60 MB/s = 240 MB/s in
> bandwidth.  That means that if you are dealing with 24,000 MB of data in the
> ?transactions? table, then you will scan  it in 100 seconds.

Why divide by 2? A good raid controller should be able to send read
requests to both drives out of the mirrored set to fully utilize the
bandwidth. Of course, that probably won't come into play unless the OS
decides that it's going to read-ahead fairly large chunks of the table
at a time...

Also, some vmstat output would certainly help clarify where the
bottleneck is...
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Mon Jan 30 18:57:23 2006
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Date: Mon, 30 Jan 2006 23:57:11 +0100
From: Emmanuel Lacour <elacour@easter-eggs.com>
To: pgsql-performance@postgresql.org
Subject: Query planner issue
Message-ID: <20060130225711.GE1320@easter-eggs.com>
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Hi everybody,

I have the following problem, on a test server, if I do a fresh import
of production data then run 
'explain analyze select count(*) from mandats;'

I get this result:

Aggregate  (cost=6487.32..6487.32 rows=1 width=0) (actual time=607.61..607.61 rows=1 loops=1)
  ->  Seq Scan on mandats  (cost=0.00..6373.26 rows=45626 width=0) (actual time=0.14..496.20 rows=45626 loops=1)
  Total runtime: 607.95 msec


On the production server, if I do the same (without other use of the server), I get:

Aggregate  (cost=227554.33..227554.33 rows=1 width=0) (actual time=230705.79..230705.79 rows=1 loops=1)
  ->  Seq Scan on mandats  (cost=0.00..227440.26 rows=45626 width=0) (actual time=0.03..230616.64 rows=45760 loops=1)
  Total runtime: 230706.08 msec



Is there anyone having an idea on how yo solve this poor performances? I
think it is caused by many delete/insert on this table every day, but
how to solve it, I need to run this qury each hour :(. I run
vacuum each night, postgresql is unfortunatly 7.2.1 :( (no upgrade
before 2 or 3 months).

-- 
Emmanuel Lacour ------------------------------------ Easter-eggs
44-46 rue de l'Ouest  -  75014 Paris   -   France -  M�tro Gait�
Phone: +33 (0) 1 43 35 00 37    -     Fax: +33 (0) 1 41 35 00 76
mailto:elacour@easter-eggs.com   -    http://www.easter-eggs.com

From pgsql-performance-owner@postgresql.org  Mon Jan 30 19:26:27 2006
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	30 Jan 2006 15:26:23 -0800
Subject: Re: Query planner issue
From: Mark Lewis <mark.lewis@mir3.com>
To: Emmanuel Lacour <elacour@easter-eggs.com>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <20060130225711.GE1320@easter-eggs.com>
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You have lots of dead rows.  Do a vacuum full to get it under control,
then run VACUUM more frequently and/or increase your FSM settings to
keep dead rows in check.  In 7.2 vacuum is pretty intrusive; it will be
much better behaved once you can upgrade to a more recent version.

You really, really want to upgrade as soon as possible, and refer to the
on-line docs about what to do with your FSM settings.

-- Mark Lewis


On Mon, 2006-01-30 at 23:57 +0100, Emmanuel Lacour wrote:
> Hi everybody,
> 
> I have the following problem, on a test server, if I do a fresh import
> of production data then run 
> 'explain analyze select count(*) from mandats;'
> 
> I get this result:
> 
> Aggregate  (cost=6487.32..6487.32 rows=1 width=0) (actual time=607.61..607.61 rows=1 loops=1)
>   ->  Seq Scan on mandats  (cost=0.00..6373.26 rows=45626 width=0) (actual time=0.14..496.20 rows=45626 loops=1)
>   Total runtime: 607.95 msec
> 
> 
> On the production server, if I do the same (without other use of the server), I get:
> 
> Aggregate  (cost=227554.33..227554.33 rows=1 width=0) (actual time=230705.79..230705.79 rows=1 loops=1)
>   ->  Seq Scan on mandats  (cost=0.00..227440.26 rows=45626 width=0) (actual time=0.03..230616.64 rows=45760 loops=1)
>   Total runtime: 230706.08 msec
> 
> 
> 
> Is there anyone having an idea on how yo solve this poor performances? I
> think it is caused by many delete/insert on this table every day, but
> how to solve it, I need to run this qury each hour :(. I run
> vacuum each night, postgresql is unfortunatly 7.2.1 :( (no upgrade
> before 2 or 3 months).
> 

From pgsql-performance-owner@postgresql.org  Mon Jan 30 19:37:31 2006
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From: "Jim Buttafuoco" <jim@contactbda.com>
To: Emmanuel Lacour <elacour@easter-eggs.com>,
 pgsql-performance@postgresql.org
Reply-To: jim@contactbda.com
Subject: Re: Query planner issue
Date: Mon, 30 Jan 2006 18:37:22 -0500
Message-Id: <20060130233550.M83895@contactbda.com>
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with Postgresql 7.2.1 you will need to do BOTH vacuum and reindex and with a table that gets many updates/deletes, you 
should run vacuum more than daily.

Both issues have been solved in 8.1.

Jim
 

---------- Original Message -----------
From: Emmanuel Lacour <elacour@easter-eggs.com>
To: pgsql-performance@postgresql.org
Sent: Mon, 30 Jan 2006 23:57:11 +0100
Subject: [PERFORM] Query planner issue

> Hi everybody,
> 
> I have the following problem, on a test server, if I do a fresh import
> of production data then run 
> 'explain analyze select count(*) from mandats;'
> 
> I get this result:
> 
> Aggregate  (cost=6487.32..6487.32 rows=1 width=0) (actual time=607.61..607.61 rows=1 loops=1)
>   ->  Seq Scan on mandats  (cost=0.00..6373.26 rows=45626 width=0) (actual time=0.14..496.20 rows=45626 
> loops=1)  Total runtime: 607.95 msec
> 
> On the production server, if I do the same (without other use of the server), I get:
> 
> Aggregate  (cost=227554.33..227554.33 rows=1 width=0) (actual time=230705.79..230705.79 rows=1 loops=1)
>   ->  Seq Scan on mandats  (cost=0.00..227440.26 rows=45626 width=0) (actual time=0.03..230616.64 rows=45760 
> loops=1)  Total runtime: 230706.08 msec
> 
> Is there anyone having an idea on how yo solve this poor performances? I
> think it is caused by many delete/insert on this table every day, but
> how to solve it, I need to run this qury each hour :(. I run
> vacuum each night, postgresql is unfortunatly 7.2.1 :( (no upgrade
> before 2 or 3 months).
> 
> -- 
> Emmanuel Lacour ------------------------------------ Easter-eggs
> 44-46 rue de l'Ouest  -  75014 Paris   -   France -  M�tro Gait�
> Phone: +33 (0) 1 43 35 00 37    -     Fax: +33 (0) 1 41 35 00 76
> mailto:elacour@easter-eggs.com   -    http://www.easter-eggs.com
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
------- End of Original Message -------


From pgsql-performance-owner@postgresql.org  Mon Jan 30 20:27:24 2006
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Date: Tue, 31 Jan 2006 01:27:25 +0100
From: Emmanuel Lacour <elacour@easter-eggs.com>
To: pgsql-performance@postgresql.org
Subject: Re: Query planner issue
Message-ID: <20060131002725.GF1320@easter-eggs.com>
References: <20060130225711.GE1320@easter-eggs.com>
	<1138663583.28241.96.camel@archimedes>
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On Mon, Jan 30, 2006 at 03:26:23PM -0800, Mark Lewis wrote:
> You have lots of dead rows.  Do a vacuum full to get it under control,
> then run VACUUM more frequently and/or increase your FSM settings to
> keep dead rows in check.  In 7.2 vacuum is pretty intrusive; it will be
> much better behaved once you can upgrade to a more recent version.
> 
> You really, really want to upgrade as soon as possible, and refer to the
> on-line docs about what to do with your FSM settings.
> 

Thanks! Vacuum full did it. I will now play with fsm settings to avoid
running a full vacuum daily...


-- 
Emmanuel Lacour ------------------------------------ Easter-eggs
44-46 rue de l'Ouest  -  75014 Paris   -   France -  M�tro Gait�
Phone: +33 (0) 1 43 35 00 37    -     Fax: +33 (0) 1 41 35 00 76
mailto:elacour@easter-eggs.com   -    http://www.easter-eggs.com

From pgsql-performance-owner@postgresql.org  Mon Jan 30 21:55:55 2006
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To: Mark Lewis <mark.lewis@mir3.com>
cc: Emmanuel Lacour <elacour@easter-eggs.com>,
 pgsql-performance@postgresql.org
Subject: Re: Query planner issue 
In-reply-to: <1138663583.28241.96.camel@archimedes> 
References: <20060130225711.GE1320@easter-eggs.com>
	<1138663583.28241.96.camel@archimedes>
Comments: In-reply-to Mark Lewis <mark.lewis@mir3.com>
	message dated "Mon, 30 Jan 2006 15:26:23 -0800"
Date: Mon, 30 Jan 2006 20:55:53 -0500
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Mark Lewis <mark.lewis@mir3.com> writes:
> You really, really want to upgrade as soon as possible,

No, sooner than that.  Show your boss the list of known
data-loss-causing bugs in 7.2.1, and refuse to take responsibility
if the database eats all your data before the "in good time" upgrade.

The release note pages starting here:
http://developer.postgresql.org/docs/postgres/release-7-2-8.html
mention the problems we found while 7.2 was still supported.  It's
likely that some of the 7.3 bugs found later than 2005-05-09 also
apply to 7.2.

			regards, tom lane

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Can you delete me from the mail list Please?


From pgsql-performance-owner@postgresql.org  Tue Jan 31 13:01:01 2006
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Date: Tue, 31 Jan 2006 09:00:30 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
cc: "Mike Biamonte" <mike@dbeat.com>,
	pgsql-performance@postgresql.org
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Jim,

On 1/30/06 12:25 PM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:

> Why divide by 2? A good raid controller should be able to send read
> requests to both drives out of the mirrored set to fully utilize the
> bandwidth. Of course, that probably won't come into play unless the OS
> decides that it's going to read-ahead fairly large chunks of the table
> at a time...

I've not seen one that does, nor would it work in the general case IMO.  In
RAID1 writes are duplicated and reads come from one of the copies.  You
could alternate read service requests to minimize rotational latency, but
you can't improve bandwidth.

- Luke   



From pgsql-performance-owner@postgresql.org  Tue Jan 31 13:39:13 2006
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Luke Lonergan wrote:
> Jim,
>
> On 1/30/06 12:25 PM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:
>
>   
>> Why divide by 2? A good raid controller should be able to send read
>> requests to both drives out of the mirrored set to fully utilize the
>> bandwidth. Of course, that probably won't come into play unless the OS
>> decides that it's going to read-ahead fairly large chunks of the table
>> at a time...
>>     
>
> I've not seen one that does, nor would it work in the general case IMO.  In
> RAID1 writes are duplicated and reads come from one of the copies.  You
> could alternate read service requests to minimize rotational latency, but
> you can't improve bandwidth.
>
> - Luke   
>
>   
For Solaris's software raid, the default settings for raid-1 sets is:  
round-robin read, parallel write.   I assumed this mean't it would give 
similar read performance to raid-0, but I've never benchmarked it.

-Kevin

From pgsql-performance-owner@postgresql.org  Tue Jan 31 14:33:18 2006
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2386429@studenti.unige.it wrote:
> Can you delete me from the mail list Please?

Go to the website.
Click "community"
Click "mailing lists"
On the left-hand side click "Subscribe"
Fill in the form, changing action to "unsubscribe"

HTH

-- 
   Richard Huxton
   Archonet Ltd

From pgsql-performance-owner@postgresql.org  Tue Jan 31 15:21:47 2006
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Date: Tue, 31 Jan 2006 13:21:45 -0600
From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Luke Lonergan <llonergan@greenplum.com>
Cc: Mike Biamonte <mike@dbeat.com>, pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
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On Tue, Jan 31, 2006 at 09:00:30AM -0800, Luke Lonergan wrote:
> Jim,
> 
> On 1/30/06 12:25 PM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:
> 
> > Why divide by 2? A good raid controller should be able to send read
> > requests to both drives out of the mirrored set to fully utilize the
> > bandwidth. Of course, that probably won't come into play unless the OS
> > decides that it's going to read-ahead fairly large chunks of the table
> > at a time...
> 
> I've not seen one that does, nor would it work in the general case IMO.  In
> RAID1 writes are duplicated and reads come from one of the copies.  You
> could alternate read service requests to minimize rotational latency, but
> you can't improve bandwidth.

(BTW, I did some testing that seems to confirm this)

Why couldn't you double the bandwidth? If you're doing a largish read
you should be able to do something like have drive a read the first
track, drive b the second, etc. Of course that means that the controller
or OS would have to be able to stitch things back together.

As for software raid, I'm wondering how well that works if you can't use
a BBU to allow write caching/re-ordering...
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 31 15:23:24 2006
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From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Richard Huxton <dev@archonet.com>
Cc: 2386429@studenti.unige.it, pgsql-performance@postgresql.org
Subject: Re: Delete me
Message-ID: <20060131192321.GV95850@pervasive.com>
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	<43DFAD6A.8000206@archonet.com>
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On Tue, Jan 31, 2006 at 06:33:14PM +0000, Richard Huxton wrote:
> 2386429@studenti.unige.it wrote:
> >Can you delete me from the mail list Please?
> 
> Go to the website.
> Click "community"
> Click "mailing lists"
> On the left-hand side click "Subscribe"
> Fill in the form, changing action to "unsubscribe"

Or take a look at the header that's included with every single message
sent to the list...

List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 31 16:04:02 2006
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Subject: Re: Huge Data sets, simple queries
From: "Jeffrey W. Baker" <jwbaker@acm.org>
To: pgsql-performance@postgresql.org
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On Tue, 2006-01-31 at 09:00 -0800, Luke Lonergan wrote:
> Jim,
> 
> On 1/30/06 12:25 PM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:
> 
> > Why divide by 2? A good raid controller should be able to send read
> > requests to both drives out of the mirrored set to fully utilize the
> > bandwidth. Of course, that probably won't come into play unless the OS
> > decides that it's going to read-ahead fairly large chunks of the table
> > at a time...
> 
> I've not seen one that does, nor would it work in the general case IMO.  In
> RAID1 writes are duplicated and reads come from one of the copies.  You
> could alternate read service requests to minimize rotational latency, but
> you can't improve bandwidth.

Then you've not seen Linux.  Linux does balanced reads on software
mirrors.  I'm not sure why you think this can't improve bandwidth.  It
does improve streaming bandwidth as long as the platter STR is more than
the bus STR.

-jwb

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Date: Tue, 31 Jan 2006 12:47:10 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Jeffrey W. Baker" <jwbaker@acm.org>,
	pgsql-performance@postgresql.org
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Jeffrey,

On 1/31/06 12:03 PM, "Jeffrey W. Baker" <jwbaker@acm.org> wrote:

> Then you've not seen Linux.

:-D

> Linux does balanced reads on software
> mirrors.  I'm not sure why you think this can't improve bandwidth.  It
> does improve streaming bandwidth as long as the platter STR is more than
> the bus STR.

... Prove it.

- Luke



From pgsql-performance-owner@postgresql.org  Tue Jan 31 18:53:15 2006
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Date: Tue, 31 Jan 2006 14:52:57 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
cc: "Mike Biamonte" <mike@dbeat.com>,
	pgsql-performance@postgresql.org
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Jim,

On 1/31/06 11:21 AM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:

> (BTW, I did some testing that seems to confirm this)
> 
> Why couldn't you double the bandwidth? If you're doing a largish read
> you should be able to do something like have drive a read the first
> track, drive b the second, etc. Of course that means that the controller
> or OS would have to be able to stitch things back together.

It's because your alternating reads are skipping in chunks across the
platter.  Disks work at their max internal rate when reading sequential
data, and the cache is often built to buffer a track-at-a-time, so
alternating pieces that are not contiguous has the effect of halving the max
internal sustained bandwidth of each drive - the total is equal to one
drive's sustained internal bandwidth.

This works differently for RAID0, where the chunks are allocated to each
drive and laid down contiguously on each, so that when they're read back,
each drive runs at it's sustained sequential throughput.

The alternating technique in mirroring might improve rotational latency for
random seeking - a trick that Tandem exploited, but it won't improve
bandwidth.
 
> As for software raid, I'm wondering how well that works if you can't use
> a BBU to allow write caching/re-ordering...

Works great with standard OS write caching.

- Luke



From pgsql-performance-owner@postgresql.org  Tue Jan 31 19:10:17 2006
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>> Linux does balanced reads on software
>> mirrors.  I'm not sure why you think this can't improve bandwidth.  It
>> does improve streaming bandwidth as long as the platter STR is more than
>> the bus STR.
>
> ... Prove it.
>

	(I have a software RAID1 on this desktop machine)

	It's a lot faster than a single disk for random reads when more than 1  
thread hits the disk, because it distributes reads to both disks. Thus,  
applications start faster, and the machine is more reactive even when the  
disk is thrashing. Cron starting a "updatedb" is less painful. It's cool  
for desktop use (and of course it's more reliable).

	However large reads (dd-style) are just the same speed as 1 drive. I  
guess you'd need a humongous readahead in order to read from both disks.

From pgsql-performance-owner@postgresql.org  Tue Jan 31 19:12:27 2006
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To: Luke Lonergan <llonergan@greenplum.com>
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On Tue, Jan 31, 2006 at 02:52:57PM -0800, Luke Lonergan wrote:
> It's because your alternating reads are skipping in chunks across the
> platter.  Disks work at their max internal rate when reading sequential
> data, and the cache is often built to buffer a track-at-a-time, so
> alternating pieces that are not contiguous has the effect of halving the max
> internal sustained bandwidth of each drive - the total is equal to one
> drive's sustained internal bandwidth.
> 
> This works differently for RAID0, where the chunks are allocated to each
> drive and laid down contiguously on each, so that when they're read back,
> each drive runs at it's sustained sequential throughput.
> 
> The alternating technique in mirroring might improve rotational latency for
> random seeking - a trick that Tandem exploited, but it won't improve
> bandwidth.

Or just work in multiples of tracks, which would greatly reduce the
impact of delays from seeking.

> > As for software raid, I'm wondering how well that works if you can't use
> > a BBU to allow write caching/re-ordering...
> 
> Works great with standard OS write caching.

Well, the only problem with that is if the machine crashes for any
reason you risk having the database corrupted (or at best losing some
committed transactions).
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

From pgsql-performance-owner@postgresql.org  Tue Jan 31 19:13:17 2006
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Date: Tue, 31 Jan 2006 15:13:10 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "PFC" <lists@peufeu.com>, "Jeffrey W. Baker" <jwbaker@acm.org>,
	pgsql-performance@postgresql.org
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PFC,

On 1/31/06 3:11 PM, "PFC" <lists@peufeu.com> wrote:

>> ... Prove it.
>> 
> 
> (I have a software RAID1 on this desktop machine)
> 
> It's a lot faster than a single disk for random reads when more than 1
> thread hits the disk, because it distributes reads to both disks. Thus,
> applications start faster, and the machine is more reactive even when the
> disk is thrashing. Cron starting a "updatedb" is less painful. It's cool
> for desktop use (and of course it's more reliable).

Exactly - improved your random seeks.

> However large reads (dd-style) are just the same speed as 1 drive. I
> guess you'd need a humongous readahead in order to read from both disks.

Nope - won't help.

- Luke



From pgsql-performance-owner@postgresql.org  Tue Jan 31 19:20:05 2006
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Date: Tue, 31 Jan 2006 15:19:38 -0800
Subject: Re: Huge Data sets, simple queries
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
cc: "Mike Biamonte" <mike@dbeat.com>,
	pgsql-performance@postgresql.org
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Jim,

On 1/31/06 3:12 PM, "Jim C. Nasby" <jnasby@pervasive.com> wrote:

>> The alternating technique in mirroring might improve rotational latency for
>> random seeking - a trick that Tandem exploited, but it won't improve
>> bandwidth.
> 
> Or just work in multiples of tracks, which would greatly reduce the
> impact of delays from seeking.

So, having rediscovered the facts underlying the age-old RAID10 versus RAID5
debate we're back to the earlier points.

RAID10 is/was the best option when latency / random seek was the predominant
problem to be solved, RAID5/50 is best where read bandwidth is needed.
Modern developments in fast CPUs for write checksumming have made RAID5/50 a
viable alternative to RAID10 even when there is moderate write / random seek
workloads and fast read is needed.
    
>> 
>> Works great with standard OS write caching.
> 
> Well, the only problem with that is if the machine crashes for any
> reason you risk having the database corrupted (or at best losing some
> committed transactions).

So, do you routinely turn off Linux write caching?  If not, then there's no
difference.

- Luke



From pgsql-performance-owner@postgresql.org  Tue Jan 31 19:51:33 2006
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Subject: partitioning and locking problems
Date: Tue, 31 Jan 2006 18:25:01 -0500
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We have a large database system designed around partitioning.  Our
application is characterized with
=20
- terabytes of data
- billions of rows in dozens of base tables (and 100s of paritions)
- 24x7 insert load of new data that cannot be stopped, data is time
sensitive.
- periodic reports that can have long running queries with query times
measured in hours
=20
We have 2 classes of "maintenance" activities that are causing us
problems:
- periodically we need to change an insert rule on a view to point to a
different partition.
- periodically we need to delete data that is no longer needed.
Performed via truncate.
=20
Under both these circumstances (truncate and create / replace rule) the
locking behaviour of these commands can cause locking problems for us.
The scenario is best illustrated as a series of steps:
=20

	1- long running report is running on view
	2- continuous inserters into view into a table via a rule
	3- truncate or rule change occurs, taking an exclusive lock.
Must wait for #1 to finish.
	4- new reports and inserters must now wait for #3.
	5- now everyone is waiting for a single query in #1.   Results
in loss of insert data granularity (important for our application).

=20
Would like to understand the implications of changing postgres'
code/locking for rule changes and truncate to not require locking out
select statements? =20
=20
The following is a simplified schema to help illustrate the problem.
=20

	create table a_1
	(
	    pkey int primary key
	);
	create table a_2
	(
	    pkey int primary key
	);
	=20
	create view a as select * from a_1 union all select * from a_2;
	=20
	create function change_rule(int) returns void as
	'
	begin
	    execute ''create or replace rule insert as on insert to a do
instead insert into a_''||$1||''(pkey) values(NEW.pkey)'';
	end;
	' language plpgsql;
	=20
	-- change rule, execute something like the following
periodically
	select change_rule(1);

=20
We've looked at the code and the rule changes appear "easy" but we are
concerned about the required changes for truncate.
=20
Thanks
Marc