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From: Keith Gray <[email protected]> |
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-- |
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Keith Gray |
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Technical Services Manager |
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Heart Consulting Services |
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From [email protected] Wed Sep 11 04:47:03 2002 |
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------------------------------------------------------------------------------ |
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> Khusus Pelanggan Telepon DIVRE 2, Tekan 166 untuk mendengarkan pesan Anda |
|
------------------------------------------------------------------------------ |
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|
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From [email protected] Fri Sep 13 20:16:03 2002 |
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Message-ID: <3D827FBF.4[email protected]> |
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Date: Sat, 14 Sep 2002 10:15:59 +1000 |
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From: Justin Clift <[email protected]> |
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To: PostgreSQL Performance Mailing List <[email protected]> |
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Subject: Anyone have any find grained benchmark data? |
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Hi everyone, |
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|
|
There are PostgreSQL servers around that are handling 2,000 simultaneous |
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client connections (in real life) without problems, but no-one obvious |
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seems to have yet taken the time to do fine grained testing of the |
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servers which can take this kind of load, to accurately model their |
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performance characteristics. |
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|
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Does anyone here happen to have fine grained benchmark/performance |
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figures hanging around which get into this range of performance? |
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Preferably with pretty precise details of how the system was configured, |
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etc. |
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|
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:-) |
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|
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Regards and best wishes, |
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|
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Justin Clift |
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|
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-- |
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"My grandfather once told me that there are two kinds of people: those |
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who work and those who take the credit. He told me to try to be in the |
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first group; there was less competition there." |
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- Indira Gandhi |
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|
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From [email protected] Tue Sep 17 06:50:17 2002 |
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------------------------------------------------------------------------------ |
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> Khusus Pelanggan Telepon DIVRE 2, Tekan 166 untuk mendengarkan pesan Anda |
|
------------------------------------------------------------------------------ |
|
|
|
From [email protected] Thu Sep 26 04:35:33 2002 |
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To: [email protected], [email protected] |
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Subject: Performance while loading data and indexing |
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|
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Hello all, |
|
|
|
Some time back I posted a query to build a site with 150GB of database. In last |
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couple of weeks, lots of things were tested at my place and there are some |
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results and again some concerns. |
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|
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This is a long post. Please be patient and read thr. If we win this, I guess we |
|
have a good marketing/advocacy case here..;-) |
|
|
|
First the problems (For those who do not read beyond first page) |
|
|
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1) Database load time from flat file using copy is very high |
|
2) Creating index takes huge amount of time. |
|
3) Any suggsestions for runtime as data load and query will be going in |
|
parallel. |
|
|
|
Now the details. Note that this is a test run only.. |
|
|
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Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI |
|
RedHat7.2/PostgreSQL7.1.3 |
|
|
|
Database in flat file: |
|
125,000,000 records of around 100 bytes each. |
|
Flat file size 12GB |
|
|
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Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec. |
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Create unique composite index on 2 char and a timestamp field: 25226 sec. |
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Database size on disk: 26GB |
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Select query: 1.5 sec. for approx. 150 rows. |
|
|
|
Important postgresql.conf settings |
|
|
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sort_mem = 12000 |
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shared_buffers = 24000 |
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fsync=true (Sad but true. Left untouched.. Will that make a difference on |
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SCSI?) |
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wal_buffers = 65536 |
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wal_files = 64 |
|
|
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Now the requirements |
|
|
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Initial flat data load: 250GB of data. This has gone up since last query. It |
|
was 150GB earlier.. |
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Ongoing inserts: 5000/sec. |
|
Number of queries: 4800 queries/hour |
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Query response time: 10 sec. |
|
|
|
|
|
Now questions. |
|
|
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1) Instead of copying from a single 12GB data file, will a parallel copy from |
|
say 5 files will speed up the things? |
|
|
|
Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 |
|
setup.. |
|
|
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2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further |
|
addition to improve create index performance? |
|
|
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3) 5K concurrent inserts with an index on, will this need a additional CPU |
|
power? Like deploying it on dual RISC CPUs etc? |
|
|
|
4) Query performance is not a problem. Though 4.8K queries per sec. expected |
|
response time from each query is 10 sec. But my guess is some serius CPU power |
|
will be chewed there too.. |
|
|
|
5)Will upgrading to 7.2.2/7.3 beta help? |
|
|
|
All in all, in the test, we didn't see the performance where hardware is |
|
saturated to it's limits. So effectively we are not able to get postgresql |
|
making use of it. Just pushing WAL and shared buffers does not seem to be the |
|
solution. |
|
|
|
If you guys have any suggestions. let me know. I need them all.. |
|
|
|
Mysql is almost out because it's creating index for last 17 hours. I don't |
|
think it will keep up with 5K inserts per sec. with index. SAP DB is under |
|
evaluation too. But postgresql is most favourite as of now because it works. So |
|
I need to come up with solutions to problems that will occur in near future.. |
|
;-) |
|
|
|
TIA.. |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Law of Procrastination: Procrastination avoids boredom; one never has the |
|
feeling that there is nothing important to do. |
|
|
|
|
|
From [email protected] Thu Sep 26 04:53:43 2002 |
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Thu, 26 Sep 2002 14:24:49 +0530 |
|
From: "Shridhar Daithankar" <[email protected]> |
|
To: [email protected], [email protected] |
|
Date: Thu, 26 Sep 2002 14:24:02 +0530 |
|
MIME-Version: 1.0 |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
Reply-To: [email protected] |
|
Message-ID: <3D931882.31859.134B9E4C@localhost> |
|
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|
|
On 26 Sep 2002 at 14:05, Shridhar Daithankar wrote: |
|
> Some time back I posted a query to build a site with 150GB of database. In last |
|
> couple of weeks, lots of things were tested at my place and there are some |
|
> results and again some concerns. |
|
|
|
> 2) Creating index takes huge amount of time. |
|
> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec. |
|
> Create unique composite index on 2 char and a timestamp field: 25226 sec. |
|
> Database size on disk: 26GB |
|
> Select query: 1.5 sec. for approx. 150 rows. |
|
|
|
> 2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further |
|
> addition to improve create index performance? |
|
|
|
Just a thought. If I sort the table before making an index, would it be faster |
|
than creating index on raw table? And/or if at all, how do I sort the table |
|
without duplicating it? |
|
|
|
Just a wild thought.. |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
linux: the choice of a GNU generation([email protected] put this on Tshirts in |
|
'93) |
|
|
|
|
|
From [email protected] Thu Sep 26 05:06:18 2002 |
|
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Date: Thu, 26 Sep 2002 19:05:19 +1000 |
|
From: Martijn van Oosterhout <[email protected]> |
|
To: Shridhar Daithankar <[email protected].in> |
|
Cc: [email protected], [email protected] |
|
Subject: Re: Performance while loading data and indexing |
|
Message-ID: <20020926090519.[email protected]> |
|
Reply-To: Martijn van Oosterhout <[email protected]> |
|
Mail-Followup-To: Shridhar Daithankar <[email protected].in>, |
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|
|
I'll preface this by saying that while I have a large database, it doesn't |
|
require quite the performace you're talking about here. |
|
|
|
On Thu, Sep 26, 2002 at 02:05:44PM +0530, Shridhar Daithankar wrote: |
|
> 1) Database load time from flat file using copy is very high |
|
> 2) Creating index takes huge amount of time. |
|
> 3) Any suggsestions for runtime as data load and query will be going in |
|
> parallel. |
|
|
|
You're loading all the data in one copy. I find that INSERTs are mostly |
|
limited by indexes. While index lookups are cheap, they are not free and |
|
each index needs to be updated for each row. |
|
|
|
I fond using partial indexes to only index the rows you actually use can |
|
help with the loading. It's a bit obscure though. |
|
|
|
As for parallel loading, you'll be limited mostly by your I/O bandwidth. |
|
Have you measured it to take sure it's up to speed? |
|
|
|
> Now the details. Note that this is a test run only.. |
|
> |
|
> Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI |
|
> RedHat7.2/PostgreSQL7.1.3 |
|
> |
|
> Database in flat file: |
|
> 125,000,000 records of around 100 bytes each. |
|
> Flat file size 12GB |
|
> |
|
> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec. |
|
> Create unique composite index on 2 char and a timestamp field: 25226 sec. |
|
> Database size on disk: 26GB |
|
> Select query: 1.5 sec. for approx. 150 rows. |
|
|
|
So you're loading at a rate of 860KB per sec. That's not too fast. How many |
|
indexes are active at that time? Triggers and foreign keys also take their |
|
toll. |
|
|
|
> Important postgresql.conf settings |
|
> |
|
> sort_mem = 12000 |
|
> shared_buffers = 24000 |
|
> fsync=true (Sad but true. Left untouched.. Will that make a difference on |
|
> SCSI?) |
|
> wal_buffers = 65536 |
|
> wal_files = 64 |
|
|
|
fsync IIRC only affects the WAL buffers now but it may be quite expensive, |
|
especially considering it's running on every transaction commit. Oh, your |
|
WAL files are on a seperate disk from the data? |
|
|
|
> Initial flat data load: 250GB of data. This has gone up since last query. It |
|
> was 150GB earlier.. |
|
> Ongoing inserts: 5000/sec. |
|
> Number of queries: 4800 queries/hour |
|
> Query response time: 10 sec. |
|
|
|
That looks quite acheivable. |
|
|
|
> 1) Instead of copying from a single 12GB data file, will a parallel copy from |
|
> say 5 files will speed up the things? |
|
|
|
Limited by I/O bandwidth. On linux vmstat can tell you how many blocks are |
|
being loaded and stored per second. Try it. As long as sync() doesn't get |
|
done too often, it should be help. |
|
|
|
> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 |
|
> setup.. |
|
|
|
No, it's not. You should be able to do better. |
|
|
|
> 2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further |
|
> addition to improve create index performance? |
|
|
|
Should be fine. Admittedly your indexes are taking rather long to build. |
|
|
|
> 3) 5K concurrent inserts with an index on, will this need a additional CPU |
|
> power? Like deploying it on dual RISC CPUs etc? |
|
|
|
It shouldn't. Do you have an idea of what your CPU usage is? ps aux should |
|
give you a decent idea. |
|
|
|
> 4) Query performance is not a problem. Though 4.8K queries per sec. expected |
|
> response time from each query is 10 sec. But my guess is some serius CPU power |
|
> will be chewed there too.. |
|
|
|
Should be fine. |
|
|
|
> 5)Will upgrading to 7.2.2/7.3 beta help? |
|
|
|
Possibly, though it may be wirth it just for the features/bugfixes. |
|
|
|
> All in all, in the test, we didn't see the performance where hardware is |
|
> saturated to it's limits. So effectively we are not able to get postgresql |
|
> making use of it. Just pushing WAL and shared buffers does not seem to be the |
|
> solution. |
|
> |
|
> If you guys have any suggestions. let me know. I need them all.. |
|
|
|
Find the bottleneck: CPU, I/O or memory? |
|
|
|
> Mysql is almost out because it's creating index for last 17 hours. I don't |
|
> think it will keep up with 5K inserts per sec. with index. SAP DB is under |
|
> evaluation too. But postgresql is most favourite as of now because it works. So |
|
> I need to come up with solutions to problems that will occur in near future.. |
|
> ;-) |
|
|
|
17 hours! Ouch. Either way, you should be able to do much better. Hope this |
|
helps, |
|
-- |
|
Martijn van Oosterhout <[email protected]> http://svana.org/kleptog/ |
|
> There are 10 kinds of people in the world, those that can do binary |
|
> arithmetic and those that can't. |
|
|
|
From [email protected] Thu Sep 26 05:12:58 2002 |
|
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Thu, 26 Sep 2002 14:44:06 +0530 |
|
From: "Shridhar Daithankar" <[email protected]> |
|
To: [email protected] |
|
Date: Thu, 26 Sep 2002 14:43:20 +0530 |
|
MIME-Version: 1.0 |
|
Subject: Re: Performance while loading data and indexing |
|
Reply-To: [email protected] |
|
Cc: [email protected] |
|
Message-ID: <3D931D08.1695.135D474B@localhost> |
|
In-reply-to: |
|
<19138.194.185.48.247.1033030286.squirrel@mail.talentwebsolutions.com> |
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|
|
On 26 Sep 2002 at 10:51, [email protected] wrote: |
|
|
|
> Hi, |
|
> it seems you have to cluster it, I don't think you have another choise. |
|
|
|
Hmm.. That didn't occur to me...I guess some real time clustering like usogres |
|
would do. Unless it turns out to be a performance hog.. |
|
|
|
But this is just insert and select. No updates no deletes(Unless customer makes |
|
a 180 degree turn) So I doubt if clustering will help. At the most I can |
|
replicate data across machines and spread queries on them. Replication overhead |
|
as a down side and low query load on each machine as upside.. |
|
|
|
> I'm retrieving the configuration of our postgres servers (I'm out of office |
|
> now), so I can send it to you. I was quite disperate about performance, and |
|
> I was thinking to migrate the data on an oracle database. Then I found this |
|
> configuration on the net, and I had a succesfull increase of performance. |
|
|
|
In this case, we are upto postgresql because we/our customer wants to keep the |
|
costs down..:-) Even they are asking now if it's possible to keep hardware |
|
costs down as well. That's getting some funny responses here but I digress.. |
|
|
|
> Maybe this can help you. |
|
> |
|
> Why you use copy to insert records? I usually use perl scripts, and they |
|
> work well . |
|
|
|
Performance reasons. As I said in one of my posts earlier, putting upto 100K |
|
records in one transaction in steps of 10K did not reach performance of copy. |
|
As Tom said rightly, it was a 4-1 ratio despite using transactions.. |
|
|
|
Thanks once again.. |
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Secretary's Revenge: Filing almost everything under "the". |
|
|
|
|
|
From [email protected] Thu Sep 26 05:17:41 2002 |
|
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Message-ID: <3[email protected]> |
|
Date: Thu, 26 Sep 2002 19:17:32 +1000 |
|
From: Justin Clift <[email protected]> |
|
X-Mailer: Mozilla 4.79 [en] (WinNT; U) |
|
X-Accept-Language: en |
|
MIME-Version: 1.0 |
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To: [email protected].in |
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Cc: [email protected], [email protected] |
|
Subject: Re: Performance while loading data and indexing |
|
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|
|
Hi Shridhar, |
|
|
|
Shridhar Daithankar wrote: |
|
<snip> |
|
> 3) Any suggsestions for runtime as data load and query will be going in |
|
> parallel. |
|
|
|
That sounds unusual. From reading this, it *sounds* like you'll be |
|
running queries against an incomplete dataset, or maybe just running the |
|
queries that affect the tables loaded thus far (during the initial |
|
load). |
|
|
|
<snip> |
|
> fsync=true (Sad but true. Left untouched.. Will that make a difference on |
|
> SCSI?) |
|
|
|
Definitely. Have directly measured a ~ 2x tps throughput increase on |
|
FreeBSD when leaving fsync off whilst performance measuring stuff |
|
recently (PG 7.2.2). Like anything it'll depend on workload, phase of |
|
moon, etc, but it's a decent indicator. |
|
|
|
<snip> |
|
> Now questions. |
|
> |
|
> 1) Instead of copying from a single 12GB data file, will a parallel copy from |
|
> say 5 files will speed up the things? |
|
|
|
Not sure yet. Haven't get done enough performance testing (on the cards |
|
very soon though). |
|
|
|
> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 |
|
> setup.. |
|
|
|
fsync = off would help during the data load, but not a good idea if |
|
you're going to be running queries against it at the same time. |
|
|
|
Am still getting the hang of performance tuning stuff. Have a bunch of |
|
Ultra160 hardware for the Intel platform, and am testing against it as |
|
time permits. |
|
|
|
Not as high end as I'd like, but it's a start. |
|
|
|
:-) |
|
|
|
Regards and best wishes, |
|
|
|
Justin Clift |
|
|
|
<snip> |
|
> Bye |
|
> Shridhar |
|
|
|
-- |
|
"My grandfather once told me that there are two kinds of people: those |
|
who work and those who take the credit. He told me to try to be in the |
|
first group; there was less competition there." |
|
- Indira Gandhi |
|
|
|
From [email protected] Thu Sep 26 05:35:14 2002 |
|
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Thu, 26 Sep 2002 15:06:26 +0530 |
|
From: "Shridhar Daithankar" <[email protected].in> |
|
To: [email protected], [email protected] |
|
Date: Thu, 26 Sep 2002 15:05:40 +0530 |
|
MIME-Version: 1.0 |
|
Subject: Re: Performance while loading data and indexing |
|
Reply-To: [email protected].in |
|
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|
|
On 26 Sep 2002 at 19:17, Justin Clift wrote: |
|
> Shridhar Daithankar wrote: |
|
> <snip> |
|
> > 3) Any suggsestions for runtime as data load and query will be going in |
|
> > parallel. |
|
> |
|
> That sounds unusual. From reading this, it *sounds* like you'll be |
|
> running queries against an incomplete dataset, or maybe just running the |
|
> queries that affect the tables loaded thus far (during the initial |
|
> load). |
|
|
|
That's correct. Load the data so far and keep inserting data as and when it |
|
generates. |
|
|
|
They don't mind running against data so far. It's not very accurate stuff |
|
IMO... |
|
|
|
> > fsync=true (Sad but true. Left untouched.. Will that make a difference on |
|
> > SCSI?) |
|
> |
|
> Definitely. Have directly measured a ~ 2x tps throughput increase on |
|
> FreeBSD when leaving fsync off whilst performance measuring stuff |
|
> recently (PG 7.2.2). Like anything it'll depend on workload, phase of |
|
> moon, etc, but it's a decent indicator. |
|
|
|
I didn't know even that matters with SCSI..Will check out.. |
|
|
|
> fsync = off would help during the data load, but not a good idea if |
|
> you're going to be running queries against it at the same time. |
|
|
|
That's OK for the reasons mentioned above. It wouldn't be out of place to |
|
expect a UPS to such an installation... |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Hoare's Law of Large Problems: Inside every large problem is a small problem |
|
struggling to get out. |
|
|
|
|
|
From [email protected] Thu Sep 26 05:46:29 2002 |
|
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Thu, 26 Sep 2002 15:17:36 +0530 |
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From: "Shridhar Daithankar" <[email protected]> |
|
To: [email protected], [email protected] |
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Date: Thu, 26 Sep 2002 15:16:50 +0530 |
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MIME-Version: 1.0 |
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Subject: Re: Performance while loading data and indexing |
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On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote: |
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> On Thu, Sep 26, 2002 at 02:05:44PM +0530, Shridhar Daithankar wrote: |
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> > 1) Database load time from flat file using copy is very high |
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> > 2) Creating index takes huge amount of time. |
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> > 3) Any suggsestions for runtime as data load and query will be going in |
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> > parallel. |
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> |
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> You're loading all the data in one copy. I find that INSERTs are mostly |
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> limited by indexes. While index lookups are cheap, they are not free and |
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> each index needs to be updated for each row. |
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> |
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> I fond using partial indexes to only index the rows you actually use can |
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> help with the loading. It's a bit obscure though. |
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> |
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> As for parallel loading, you'll be limited mostly by your I/O bandwidth. |
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> Have you measured it to take sure it's up to speed? |
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Well. It's like this, as of now.. CreateDB->create table->create index->Select. |
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So loading is not slowed by index. As of your hint of vmstat, will check it |
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out. |
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> So you're loading at a rate of 860KB per sec. That's not too fast. How many |
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> indexes are active at that time? Triggers and foreign keys also take their |
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> toll. |
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Nothing except the table where data os loaded.. |
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> fsync IIRC only affects the WAL buffers now but it may be quite expensive, |
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> especially considering it's running on every transaction commit. Oh, your |
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> WAL files are on a seperate disk from the data? |
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No. Same RAID 5 disks.. |
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> It shouldn't. Do you have an idea of what your CPU usage is? ps aux should |
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> give you a decent idea. |
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I guess we forgot to monitor system parameters. Next on my list is running |
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vmstat, top and tuning bdflush. |
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> Find the bottleneck: CPU, I/O or memory? |
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Understood.. |
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> |
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> > Mysql is almost out because it's creating index for last 17 hours. I don't |
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> > think it will keep up with 5K inserts per sec. with index. SAP DB is under |
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> > evaluation too. But postgresql is most favourite as of now because it works. So |
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> > I need to come up with solutions to problems that will occur in near future.. |
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> > ;-) |
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> |
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> 17 hours! Ouch. Either way, you should be able to do much better. Hope this |
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> helps, |
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Heh.. no wonder this evaluation is taking more than 2 weeks.. Mysql was running |
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out of disk space while creating index and crashin. An upgrade to mysql helped |
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there but no numbers as yet.. |
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Thanks once again... |
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Bye |
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Shridhar |
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-- |
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Boren's Laws: (1) When in charge, ponder. (2) When in trouble, delegate. (3) |
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When in doubt, mumble. |
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From [email protected] Thu Sep 26 05:59:51 2002 |
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From: Richard Huxton <[email protected]> |
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Organization: Archonet Ltd |
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To: [email protected], |
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[email protected] |
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Subject: Re: Performance while loading data and indexing |
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Date: Thu, 26 Sep 2002 10:48:06 +0100 |
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On Thursday 26 Sep 2002 9:35 am, Shridhar Daithankar wrote: |
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[questions re: large database] |
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Before reading my advice please bear in mind you are operating way beyond t= |
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he=20 |
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scale of anything I have ever built. |
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> Now the details. Note that this is a test run only.. |
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> |
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> Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI |
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> RedHat7.2/PostgreSQL7.1.3 |
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> |
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> Database in flat file: |
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> 125,000,000 records of around 100 bytes each. |
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> Flat file size 12GB |
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> |
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> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec. |
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> Create unique composite index on 2 char and a timestamp field: 25226 sec. |
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> Database size on disk: 26GB |
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> Select query: 1.5 sec. for approx. 150 rows. |
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> |
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> Important postgresql.conf settings |
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[snipped setting details for moment] |
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Have you tried putting the wal files, syslog etc on separate disks/volumes?= |
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If=20 |
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you've settled on Intel, about the only thing you can optimise further is t= |
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he=20 |
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disks. |
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Oh - and the OS - make sure you're running a (good) recent kernel for that= |
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=20 |
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sort of hardware, I seem to remember some substantial changes in the 2.4=20 |
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series regarding multi-processor. |
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|
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> Now the requirements |
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> |
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> Initial flat data load: 250GB of data. This has gone up since last query. |
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> It was 150GB earlier.. |
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> Ongoing inserts: 5000/sec. |
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> Number of queries: 4800 queries/hour |
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> Query response time: 10 sec. |
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Is this 5000 rows in say 500 transactions or 5000 insert transactions per= |
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=20 |
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second. How many concurrent clients is this? Similarly for the 4800 queries= |
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,=20 |
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how many concurrent clients is this? Are they expected to return approx 150= |
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=20 |
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rows as in your test? |
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> Now questions. |
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> |
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> 1) Instead of copying from a single 12GB data file, will a parallel copy |
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> from say 5 files will speed up the things? |
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If the CPU is the bottle-neck then it should, but it's difficult to say=20 |
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without figures. |
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> Couple MB of data per sec. to disk is just not saturating it. It's a RAID= |
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5 |
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> setup.. |
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What is saturating during the flat-file load? Something must be maxed in to= |
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p /=20 |
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iostat / vmstat. |
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[snip] |
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> |
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> 5)Will upgrading to 7.2.2/7.3 beta help? |
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It's unlikely to hurt. |
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> All in all, in the test, we didn't see the performance where hardware is |
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> saturated to it's limits. |
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Something *must* be. |
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What are your disaster recovery plans? I can see problems with taking backu= |
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ps=20 |
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if this beast is live 24/7. |
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- Richard Huxton |
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From [email protected] Thu Sep 26 05:50:02 2002 |
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Message-ID: <3D92D841.3E02[email protected]> |
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Date: Thu, 26 Sep 2002 19:49:53 +1000 |
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From: Justin Clift <[email protected]> |
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To: [email protected].in |
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Subject: Re: [HACKERS] Performance while loading data and indexing |
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Shridhar Daithankar wrote: |
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<snip> |
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> > > fsync=true (Sad but true. Left untouched.. Will that make a difference on |
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> > > SCSI?) |
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> > |
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> > Definitely. Have directly measured a ~ 2x tps throughput increase on |
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> > FreeBSD when leaving fsync off whilst performance measuring stuff |
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> > recently (PG 7.2.2). Like anything it'll depend on workload, phase of |
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> > moon, etc, but it's a decent indicator. |
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> |
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> I didn't know even that matters with SCSI..Will check out.. |
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Cool. When testing it had FreeBSD 4.6.2 installed on one drive along |
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with the PostgreSQL 7.2.2 binaries, it had the data on a second drive |
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(mounted as /pgdata), and it had the pg_xlog directory mounted on a |
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third drive. Swap had it's own drive as well. |
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Everything is UltraSCSI, etc. Haven't yet tested for a performance |
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difference through moving the indexes to another drive after creation |
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though. That apparently has the potential to help as well. |
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:-) |
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Regards and best wishes, |
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Justin Clift |
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-- |
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"My grandfather once told me that there are two kinds of people: those |
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who work and those who take the credit. He told me to try to be in the |
|
first group; there was less competition there." |
|
- Indira Gandhi |
|
|
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From [email protected] Thu Sep 26 05:56:37 2002 |
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Date: Thu, 26 Sep 2002 19:56:34 +1000 |
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From: Justin Clift <[email protected]> |
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To: [email protected] |
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Subject: Re: [HACKERS] Performance while loading data and indexing |
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|
|
Shridhar Daithankar wrote: |
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> |
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> On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote: |
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<snip> |
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> > fsync IIRC only affects the WAL buffers now but it may be quite expensive, |
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> > especially considering it's running on every transaction commit. Oh, your |
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> > WAL files are on a seperate disk from the data? |
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> |
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> No. Same RAID 5 disks.. |
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|
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Not sure if this is a good idea. Would have to think deeply about the |
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controller and drive optimisation/load characteristics. |
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|
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If it's any help, when I was testing recently with WAL on a separate |
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drive, the WAL logs were doing more read&writes per second than the main |
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data drive. This would of course be affected by the queries you are |
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running against the database. I was just running Tatsuo's TPC-B stuff, |
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and the OSDB AS3AP tests. |
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|
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> I guess we forgot to monitor system parameters. Next on my list is running |
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> vmstat, top and tuning bdflush. |
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|
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That'll just be the start of it for serious performance tuning and |
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learning how PostgreSQL works. :) |
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|
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<snip> |
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> Thanks once again... |
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> Bye |
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> Shridhar |
|
|
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-- |
|
"My grandfather once told me that there are two kinds of people: those |
|
who work and those who take the credit. He told me to try to be in the |
|
first group; there was less competition there." |
|
- Indira Gandhi |
|
|
|
From [email protected] Thu Sep 26 10:34:21 2002 |
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To: [email protected] |
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Cc: [email protected], [email protected] |
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Subject: Re: Performance while loading data and indexing |
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In-reply-to: <3D931438.22010.133ADAFA@localhost> |
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References: <3D931438.22010.133ADAFA@localhost> |
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Comments: In-reply-to "Shridhar Daithankar" |
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<[email protected]> |
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message dated "Thu, 26 Sep 2002 14:05:44 +0530" |
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Date: Thu, 26 Sep 2002 10:33:58 -0400 |
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Message-ID: <[email protected]> |
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From: Tom Lane <[email protected]> |
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"Shridhar Daithankar" <[email protected]> writes: |
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> RedHat7.2/PostgreSQL7.1.3 |
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|
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I'd suggest a newer release of Postgres ... 7.1.3 is pretty old ... |
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|
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> Create unique composite index on 2 char and a timestamp field: 25226 sec. |
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|
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What do you mean by "char" exactly? If it's really char(N), how much |
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are you paying in padding space? There are very very few cases where |
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I'd not say to use varchar(N), or text, instead. Also, does it have to |
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be character data? If you could use an integer or float datatype |
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instead the index operations should be faster (though I can't say by |
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how much). Have you thought carefully about the order in which the |
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composite index columns are listed? |
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|
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> sort_mem = 12000 |
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|
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To create an index of this size, you want to push sort_mem as high as it |
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can go without swapping. 12000 sounds fine for the global setting, but |
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in the process that will create the index, try setting sort_mem to some |
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hundreds of megs or even 1Gb. (But be careful: the calculation of space |
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actually used by CREATE INDEX is off quite a bit in pre-7.3 releases |
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:-(. You should probably expect the actual process size to grow to two |
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or three times what you set sort_mem to. Don't let it get so big as to |
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swap.) |
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|
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> wal_buffers = 65536 |
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|
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The above is a complete waste of memory space, which would be better |
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spent on letting the kernel expand its disk cache. There's no reason |
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for wal_buffers to be more than a few dozen. |
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|
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regards, tom lane |
|
|
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From [email protected] Thu Sep 26 10:42:11 2002 |
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To: Justin Clift <[email protected]> |
|
Cc: [email protected], |
|
[email protected], [email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-reply-to: <[email protected]> |
|
References: <3D931438.22010.133ADAFA@localhost> |
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<3D9324E2.30195.137BF348@localhost> |
|
<[email protected]> |
|
Comments: In-reply-to Justin Clift <[email protected]> |
|
message dated "Thu, 26 Sep 2002 19:56:34 +1000" |
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Date: Thu, 26 Sep 2002 10:42:08 -0400 |
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Message-ID: <[email protected]> |
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From: Tom Lane <[email protected]> |
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|
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Justin Clift <[email protected]> writes: |
|
>> On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote: |
|
>>> fsync IIRC only affects the WAL buffers now but it may be quite expensive, |
|
>>> especially considering it's running on every transaction commit. Oh, your |
|
>>> WAL files are on a seperate disk from the data? |
|
|
|
> Not sure if this is a good idea. Would have to think deeply about the |
|
> controller and drive optimisation/load characteristics. |
|
|
|
> If it's any help, when I was testing recently with WAL on a separate |
|
> drive, the WAL logs were doing more read&writes per second than the main |
|
> data drive. |
|
|
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... but way fewer seeks. For anything involving lots of updating |
|
transactions (and certainly 5000 separate insertions per second would |
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qualify; can those be batched??), it should be a win to put WAL on its |
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own spindle, just to get locality of access to the WAL. |
|
|
|
regards, tom lane |
|
|
|
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From: "Shridhar Daithankar" <[email protected]> |
|
To: [email protected], [email protected] |
|
Date: Thu, 26 Sep 2002 20:22:05 +0530 |
|
MIME-Version: 1.0 |
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Subject: Re: Performance while loading data and indexing |
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On 26 Sep 2002 at 10:33, Tom Lane wrote: |
|
|
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> "Shridhar Daithankar" <[email protected]> writes: |
|
> > RedHat7.2/PostgreSQL7.1.3 |
|
> |
|
> I'd suggest a newer release of Postgres ... 7.1.3 is pretty old ... |
|
|
|
I agree.. downloadind 7.2.2 right away.. |
|
|
|
> > Create unique composite index on 2 char and a timestamp field: 25226 sec. |
|
> |
|
> What do you mean by "char" exactly? If it's really char(N), how much |
|
> are you paying in padding space? There are very very few cases where |
|
> I'd not say to use varchar(N), or text, instead. Also, does it have to |
|
> be character data? If you could use an integer or float datatype |
|
> instead the index operations should be faster (though I can't say by |
|
> how much). Have you thought carefully about the order in which the |
|
> composite index columns are listed? |
|
|
|
I have forwarded the idea of putting things into number. If it causes speedup |
|
in index lookup/creation, it would do. Looks like bigint is the order of the |
|
day.. |
|
|
|
> |
|
> > sort_mem = 12000 |
|
> |
|
> To create an index of this size, you want to push sort_mem as high as it |
|
> can go without swapping. 12000 sounds fine for the global setting, but |
|
> in the process that will create the index, try setting sort_mem to some |
|
> hundreds of megs or even 1Gb. (But be careful: the calculation of space |
|
> actually used by CREATE INDEX is off quite a bit in pre-7.3 releases |
|
> :-(. You should probably expect the actual process size to grow to two |
|
> or three times what you set sort_mem to. Don't let it get so big as to |
|
> swap.) |
|
|
|
Great. I was skeptical to push it beyond 100MB. Now I can push it to corners.. |
|
|
|
> > wal_buffers = 65536 |
|
> |
|
> The above is a complete waste of memory space, which would be better |
|
> spent on letting the kernel expand its disk cache. There's no reason |
|
> for wal_buffers to be more than a few dozen. |
|
|
|
That was a rather desparate move. Nothing was improving performance and then we |
|
started pushing numbers.. WIll get it back.. Same goes for 64 WAL files.. A GB |
|
looks like waste to me.. |
|
|
|
I might have found the bottleneck, although by accident. Mysql was running out |
|
of space while creating index. So my friend shut down mysql and tried to move |
|
things by hand to create links. He noticed that even things like cp were |
|
terribly slow and it hit us.. May be the culprit is the file system. Ext3 in |
|
this case. |
|
|
|
My friend argues for ext2 to eliminate journalling overhead but I favour |
|
reiserfs personally having used it in pgbench with 10M rows on paltry 20GB IDE |
|
disk for 25 tps.. |
|
|
|
We will be attempting raiserfs and/or XFS if required. I know how much speed |
|
difference exists between resiserfs and ext2. Would not be surprised if |
|
everythng just starts screaming in one go.. |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Cropp's Law: The amount of work done varies inversly with the time spent in the |
|
office. |
|
|
|
|
|
From [email protected] Thu Sep 26 10:57:42 2002 |
|
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Thu, 26 Sep 2002 20:28:58 +0530 |
|
From: "Shridhar Daithankar" <[email protected].in> |
|
To: [email protected], [email protected] |
|
Date: Thu, 26 Sep 2002 20:28:11 +0530 |
|
MIME-Version: 1.0 |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
Reply-To: [email protected].in |
|
Message-ID: <3D936DDB.26585.14990280@localhost> |
|
References: <3D92D9D2.64[email protected]> |
|
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|
|
On 26 Sep 2002 at 10:42, Tom Lane wrote: |
|
|
|
> Justin Clift <[email protected]> writes: |
|
> > If it's any help, when I was testing recently with WAL on a separate |
|
> > drive, the WAL logs were doing more read&writes per second than the main |
|
> > data drive. |
|
> |
|
> ... but way fewer seeks. For anything involving lots of updating |
|
> transactions (and certainly 5000 separate insertions per second would |
|
> qualify; can those be batched??), it should be a win to put WAL on its |
|
> own spindle, just to get locality of access to the WAL. |
|
|
|
Probably they will be a single transcation. If possible we will bunch more of |
|
them together.. like 5 seconds of data pushed down in a single transaction but |
|
not sure it's possible.. |
|
|
|
This is bit like replication but from live oracle machine to postgres, from |
|
information I have. So there should be some chance of tuning there.. |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Langsam's Laws: (1) Everything depends. (2) Nothing is always. (3) Everything |
|
is sometimes. |
|
|
|
|
|
From [email protected] Thu Sep 26 11:07:07 2002 |
|
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charset="iso-8859-1" |
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From: Denis Perchine <[email protected]> |
|
Organization: AcademSoft Ltd. |
|
To: [email protected], |
|
[email protected], [email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
Date: Thu, 26 Sep 2002 22:04:41 +0700 |
|
User-Agent: KMail/1.4.3 |
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<3D936C6D.12380.14936AEC@localhost> |
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|
|
On Thursday 26 September 2002 21:52, Shridhar Daithankar wrote: |
|
|
|
> I might have found the bottleneck, although by accident. Mysql was running |
|
> out of space while creating index. So my friend shut down mysql and tried |
|
> to move things by hand to create links. He noticed that even things like cp |
|
> were terribly slow and it hit us.. May be the culprit is the file system. |
|
> Ext3 in this case. |
|
> |
|
> My friend argues for ext2 to eliminate journalling overhead but I favour |
|
> reiserfs personally having used it in pgbench with 10M rows on paltry 20GB |
|
> IDE disk for 25 tps.. |
|
> |
|
> We will be attempting raiserfs and/or XFS if required. I know how much |
|
> speed difference exists between resiserfs and ext2. Would not be surprised |
|
> if everythng just starts screaming in one go.. |
|
|
|
As it was found by someone before any non-journaling FS is faster than |
|
journaling one. This due to double work done by FS and database. |
|
|
|
Try it on ext2 and compare. |
|
|
|
-- |
|
Denis |
|
|
|
|
|
From [email protected] Thu Sep 26 11:12:48 2002 |
|
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Message-ID: <[email protected]> |
|
Date: Fri, 27 Sep 2002 01:12:49 +1000 |
|
From: Justin Clift <[email protected]> |
|
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|
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To: [email protected], |
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PostgreSQL Performance Mailing List <[email protected]> |
|
Cc: PostgreSQL Hackers Mailing List <[email protected]>, |
|
PostgreSQL General Mailing List <[email protected]> |
|
Subject: Re: Performance while loading data and indexing |
|
References: <3D931438.22010.133ADAFA@localhost> |
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<3D936C6D.12380.14936AEC@localhost> |
|
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|
|
Shridhar Daithankar wrote: |
|
<snip> |
|
> My friend argues for ext2 to eliminate journalling overhead but I favour |
|
> reiserfs personally having used it in pgbench with 10M rows on paltry 20GB IDE |
|
> disk for 25 tps.. |
|
|
|
If it's any help, the setup I mentioned before with differnt disks for |
|
the data and the WAL files was getting an average of about 72 tps with |
|
200 concurrent users on pgbench. Haven't tuned it in a hard core way at |
|
all, and it only has 256MB DDR RAM in it at the moment (single CPU |
|
AthonXP 1600). These are figures made during the 2.5k+ test runs of |
|
pgbench done when developing pg_autotune recently. |
|
|
|
As a curiosity point, how predictable are the queries you're going to be |
|
running on your database? They sound very simple and very predicatable. |
|
|
|
The pg_autotune tool might be your friend here. It can deal with |
|
arbitrary SQL instead of using the pg_bench stuff of Tatsuos, and it can |
|
also deal with an already loaded database. You'd just have to tweak the |
|
names of the tables that it vacuums and the names of the indexes that it |
|
reindexes between each run, to get some idea of your overall server |
|
performance at different load points. |
|
|
|
Probably worth taking a good look at if you're not afraid of editing |
|
variables in C code. :) |
|
|
|
> We will be attempting raiserfs and/or XFS if required. I know how much speed |
|
> difference exists between resiserfs and ext2. Would not be surprised if |
|
> everythng just starts screaming in one go.. |
|
|
|
We'd all probably be interested to hear this. Added the PostgreSQL |
|
"Performance" mailing list to this thread too, Just In Case. (wow that's |
|
a lot of cross posting now). |
|
|
|
Regards and best wishes, |
|
|
|
Justin Clift |
|
|
|
> Bye |
|
> Shridhar |
|
> |
|
> -- |
|
> Cropp's Law: The amount of work done varies inversly with the time spent in the |
|
> office. |
|
> |
|
> ---------------------------(end of broadcast)--------------------------- |
|
> TIP 3: if posting/reading through Usenet, please send an appropriate |
|
> subscribe-nomail command to [email protected] so that your |
|
> message can get through to the mailing list cleanly |
|
|
|
-- |
|
"My grandfather once told me that there are two kinds of people: those |
|
who work and those who take the credit. He told me to try to be in the |
|
first group; there was less competition there." |
|
- Indira Gandhi |
|
|
|
From [email protected] Thu Sep 26 11:28:32 2002 |
|
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Thu, 26 Sep 2002 20:59:48 +0530 |
|
From: "Shridhar Daithankar" <[email protected]> |
|
To: PostgreSQL Performance Mailing List <[email protected]> |
|
Date: Thu, 26 Sep 2002 20:59:01 +0530 |
|
MIME-Version: 1.0 |
|
Subject: Re: Performance while loading data and indexing |
|
Reply-To: [email protected] |
|
Cc: PostgreSQL Hackers Mailing List <[email protected]>, |
|
PostgreSQL General Mailing List <[email protected]> |
|
Message-ID: <3D937515.11546.14B53C07@localhost> |
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|
|
On 27 Sep 2002 at 1:12, Justin Clift wrote: |
|
|
|
> Shridhar Daithankar wrote: |
|
> As a curiosity point, how predictable are the queries you're going to be |
|
> running on your database? They sound very simple and very predicatable. |
|
|
|
Mostly predictable selects. Not a domain expert on telecom so not very sure. |
|
But in my guess prepare statement in 7.3 should come pretty handy. i.e. by the |
|
time we finish evaluation and test deployment, 7.3 will be out in next couple |
|
of months to say so. So I would recommend doing it 7.3 way only.. |
|
> |
|
> The pg_autotune tool might be your friend here. It can deal with |
|
> arbitrary SQL instead of using the pg_bench stuff of Tatsuos, and it can |
|
> also deal with an already loaded database. You'd just have to tweak the |
|
> names of the tables that it vacuums and the names of the indexes that it |
|
> reindexes between each run, to get some idea of your overall server |
|
> performance at different load points. |
|
> |
|
> Probably worth taking a good look at if you're not afraid of editing |
|
> variables in C code. :) |
|
|
|
Gladly. We started with altering pgbench here for testing and rapidly settled |
|
to perl generated random queries. Once postgresql wins the evaluation match and |
|
things come to implementation, pg_autotune would be a handy tool. Just that |
|
can't do it right now. Have to fight mysql and SAP DB before that.. |
|
|
|
BTW any performance figures on SAP DB? People here are as it frustrated with it |
|
with difficulties in setting it up. But still.. |
|
> |
|
|
|
> > We will be attempting raiserfs and/or XFS if required. I know how much speed |
|
> > difference exists between resiserfs and ext2. Would not be surprised if |
|
> > everythng just starts screaming in one go.. |
|
> |
|
> We'd all probably be interested to hear this. Added the PostgreSQL |
|
> "Performance" mailing list to this thread too, Just In Case. (wow that's |
|
> a lot of cross posting now). |
|
|
|
I know..;-) Glad that PG list does not have strict policies like no non- |
|
subscriber posting or no attachments.. etc.. |
|
|
|
IMO reiserfs, though journalling one, is faster than ext2 etc. because the way |
|
it handles metadata. Personally I haven't come across ext2 being faster than |
|
reiserfs on few machine here for day to day use. |
|
|
|
I guess I should have a freeBSD CD handy too.. Just to give it a try. If it |
|
comes down to a better VM.. though using 2.4.19 here.. so souldn't matter |
|
much.. |
|
|
|
I will keep you guys posted on file system stuff... Glad that we have much |
|
flexibility with postgresql.. |
|
|
|
Bye |
|
Shridhar |
|
|
|
-- |
|
Bilbo's First Law: You cannot count friends that are all packed up in barrels. |
|
|
|
|
|
From [email protected] Thu Sep 26 11:41:47 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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26 Sep 2002 10:41:32 -0500 |
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(CDT).200209261541[email protected]. |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
From: Greg Copeland <[email protected]> |
|
To: [email protected].in |
|
Cc: PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
In-Reply-To: <3D936C6D.12380.14936AEC@localhost> |
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|
|
On Thu, 2002-09-26 at 09:52, Shridhar Daithankar wrote: |
|
> My friend argues for ext2 to eliminate journalling overhead but I favour= |
|
=20 |
|
> reiserfs personally having used it in pgbench with 10M rows on paltry 20G= |
|
B IDE=20 |
|
> disk for 25 tps.. |
|
>=20 |
|
> We will be attempting raiserfs and/or XFS if required. I know how much sp= |
|
eed=20 |
|
> difference exists between resiserfs and ext2. Would not be surprised if= |
|
=20 |
|
> everythng just starts screaming in one go.. |
|
>=20 |
|
|
|
I'm not sure about reiserfs or ext3 but with XFS, you can create your |
|
log on another disk. Also worth noting is that you can also configure |
|
the size and number of log buffers. There are also some other |
|
performance type enhancements you can fiddle with if you don't mind |
|
risking time stamp consistency in the event of a crash. If your setup |
|
allows for it, you might want to consider using XFS in this |
|
configuration. |
|
|
|
While I have not personally tried moving XFS' log to another device, |
|
I've heard that performance gains can be truly stellar. Assuming memory |
|
allows, twiddling with the log buffering is said to allow for large |
|
strides in performance as well. |
|
|
|
If you do try this, I'd love to hear back about your results and |
|
impressions. |
|
|
|
Greg |
|
|
|
|
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From [email protected] Thu Sep 26 12:42:01 2002 |
|
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|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <[email protected]> |
|
Subject: Re: Performance while loading data and indexing |
|
In-Reply-To: <3D936C6D.12380.14936AEC@localhost> |
|
To: [email protected] |
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Date: Thu, 26 Sep 2002 12:41:34 -0400 (EDT) |
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Shridhar Daithankar wrote: |
|
> I might have found the bottleneck, although by accident. Mysql was running out |
|
> of space while creating index. So my friend shut down mysql and tried to move |
|
> things by hand to create links. He noticed that even things like cp were |
|
> terribly slow and it hit us.. May be the culprit is the file system. Ext3 in |
|
> this case. |
|
|
|
I just added a file system and multi-cpu section to my performance |
|
tuning paper: |
|
|
|
http://www.ca.postgresql.org/docs/momjian/hw_performance/ |
|
|
|
The paper does recommend ext3, but the differences between file systems |
|
are very small. If you are seeing 'cp' as slow, I wonder if it may be |
|
something more general, like poorly tuned hardware or something. You can |
|
use 'dd' to throw some data around the file system and see if that is |
|
showing slowness; compare those numbers to another machine that has |
|
different hardware/OS. |
|
|
|
Also, though ext3 is slower, turning fsync off should make ext3 function |
|
similar to ext2. That would be an interesting test if you suspect ext3. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 13:17:12 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
|
by postgresql.org (Postfix) with ESMTP |
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To: Greg Copeland <[email protected]> |
|
From: Doug cNaught <[email protected]> |
|
Cc: [email protected], |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <3D931438.22010.133ADAFA@localhost> |
|
<3D936C6D.12380.14936AEC@localhost> |
|
<[email protected]> |
|
Date: 26 Sep 2002 13:16:36 -0400 |
|
In-Reply-To: Greg Copeland's message of "26 Sep 2002 10:41:37 -0500" |
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Message-ID: <[email protected]> |
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Greg Copeland <[email protected]> writes: |
|
|
|
> I'm not sure about reiserfs or ext3 but with XFS, you can create your |
|
> log on another disk. Also worth noting is that you can also configure |
|
> the size and number of log buffers. There are also some other |
|
> performance type enhancements you can fiddle with if you don't mind |
|
> risking time stamp consistency in the event of a crash. If your setup |
|
> allows for it, you might want to consider using XFS in this |
|
> configuration. |
|
|
|
You can definitely put the ext3 log on a different disk with 2.4 |
|
kernels. |
|
|
|
Also, if you put the WAL logs on a different disk from the main |
|
database, and mount that partition with 'data=writeback' (ie |
|
metadata-only journaling) ext3 should be pretty fast, since WAL files |
|
are preallocated and there will therefore be almost no metadata |
|
updates. |
|
|
|
You should be able to mount the main database with "data=ordered" (the |
|
default) for good performance and reasonable safety. |
|
|
|
I think putting WAL on its own disk(s) is one of the keys here. |
|
|
|
-Doug |
|
|
|
From [email protected] Thu Sep 26 14:14:21 2002 |
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26 Sep 2002 12:36:51 -0500 |
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(CDT).200209261736[email protected]. |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
From: Greg Copeland <[email protected]> |
|
To: Bruce Momjian <[email protected]> |
|
Cc: [email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
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In-Reply-To: <200209261641.[email protected]> |
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References: <200209261641.[email protected]> |
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On Thu, 2002-09-26 at 11:41, Bruce Momjian wrote: |
|
> Shridhar Daithankar wrote: |
|
> > I might have found the bottleneck, although by accident. Mysql was runn= |
|
ing out=20 |
|
> > of space while creating index. So my friend shut down mysql and tried t= |
|
o move=20 |
|
> > things by hand to create links. He noticed that even things like cp wer= |
|
e=20 |
|
> > terribly slow and it hit us.. May be the culprit is the file system. Ex= |
|
t3 in=20 |
|
> > this case.=20 |
|
>=20 |
|
> I just added a file system and multi-cpu section to my performance |
|
> tuning paper: |
|
>=20 |
|
> http://www.ca.postgresql.org/docs/momjian/hw_performance/ |
|
>=20 |
|
> The paper does recommend ext3, but the differences between file systems |
|
> are very small. If you are seeing 'cp' as slow, I wonder if it may be |
|
> something more general, like poorly tuned hardware or something. You can |
|
> use 'dd' to throw some data around the file system and see if that is |
|
> showing slowness; compare those numbers to another machine that has |
|
> different hardware/OS. |
|
|
|
|
|
That's a good point. Also, if you're using IDE, you do need to verify |
|
that you're using DMA and proper PIO mode if at possible. Also, big |
|
performance improvements can be seen by making sure your IDE bus speed |
|
has been properly configured. The drivetweak-gtk and hdparm utilities |
|
can make huge difference in performance. Just be sure you know what the |
|
heck your doing when you mess with those. |
|
|
|
Greg |
|
|
|
|
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=HFjK |
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|
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From [email protected] Thu Sep 26 14:13:31 2002 |
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(CDT)[email protected]. |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
From: Greg Copeland <[email protected]> |
|
To: Bruce Momjian <[email protected]> |
|
Cc: [email protected], |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
In-Reply-To: <[email protected]> |
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|
|
On Thu, 2002-09-26 at 11:41, Bruce Momjian wrote: |
|
> Shridhar Daithankar wrote: |
|
> > I might have found the bottleneck, although by accident. Mysql was runn= |
|
ing out=20 |
|
> > of space while creating index. So my friend shut down mysql and tried t= |
|
o move=20 |
|
> > things by hand to create links. He noticed that even things like cp wer= |
|
e=20 |
|
> > terribly slow and it hit us.. May be the culprit is the file system. Ex= |
|
t3 in=20 |
|
> > this case.=20 |
|
>=20 |
|
> I just added a file system and multi-cpu section to my performance |
|
> tuning paper: |
|
>=20 |
|
> http://www.ca.postgresql.org/docs/momjian/hw_performance/ |
|
>=20 |
|
> The paper does recommend ext3, but the differences between file systems |
|
> are very small. If you are seeing 'cp' as slow, I wonder if it may be |
|
> something more general, like poorly tuned hardware or something. You can |
|
> use 'dd' to throw some data around the file system and see if that is |
|
> showing slowness; compare those numbers to another machine that has |
|
> different hardware/OS. |
|
>=20 |
|
> Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> similar to ext2. That would be an interesting test if you suspect ext3. |
|
|
|
I'm curious as to why you recommended ext3 versus some other (JFS, |
|
XFS). Do you have tests which validate that recommendation or was it a |
|
simple matter of getting the warm fuzzies from familiarity? |
|
|
|
Greg |
|
|
|
|
|
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|
From [email protected] Thu Sep 26 14:46:12 2002 |
|
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Date: Thu, 26 Sep 2002 12:41:55 -0600 (MDT) |
|
From: "scott.marlowe" <[email protected]> |
|
To: Shridhar Daithankar <[email protected].in> |
|
Cc: <[email protected]>, <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <3D931882.31859.134B9E4C@localhost> |
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|
|
If you are seeing very slow performance on a drive set, check dmesg to see |
|
if you're getting SCSI bus errors or something similar. If your drives |
|
aren't properly terminated then the performance will suffer a great deal. |
|
|
|
|
|
From [email protected] Thu Sep 26 16:01:20 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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|
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|
Thu, 26 Sep 2002 16:00:48 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262000.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <1033062262.23475.16[email protected]> |
|
To: Greg Copeland <[email protected]> |
|
Date: Thu, 26 Sep 2002 16:00:48 -0400 (EDT) |
|
Cc: [email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
X-Mailer: ELM [version 2.4ME+ PL99 (25)] |
|
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--ELM1033070448-26881-0_ |
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|
|
Greg Copeland wrote: |
|
> > The paper does recommend ext3, but the differences between file systems |
|
> > are very small. If you are seeing 'cp' as slow, I wonder if it may be |
|
> > something more general, like poorly tuned hardware or something. You can |
|
> > use 'dd' to throw some data around the file system and see if that is |
|
> > showing slowness; compare those numbers to another machine that has |
|
> > different hardware/OS. |
|
> > |
|
> > Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> > similar to ext2. That would be an interesting test if you suspect ext3. |
|
> |
|
> I'm curious as to why you recommended ext3 versus some other (JFS, |
|
> XFS). Do you have tests which validate that recommendation or was it a |
|
> simple matter of getting the warm fuzzies from familiarity? |
|
|
|
I used the attached email as a reference. I just changed the wording to |
|
be: |
|
|
|
File system choice is particularly difficult on Linux because there are |
|
so many file system choices, and none of them are optimal: ext2 is not |
|
entirely crash-safe, ext3 and xfs are journal-based, and Reiser is |
|
optimized for small files. Fortunately, the journaling file systems |
|
aren't significantly slower than ext2 so they are probably the best |
|
choice. |
|
|
|
so I don't specifically recommend ext3 anymore. As I remember, ext3 is |
|
good only in that it can read ext2 file systems. I think XFS may be the |
|
best bet. |
|
|
|
Can anyone clarify if "data=writeback" is safe for PostgreSQL. |
|
Specifically, are the data files recovered properly or is this option |
|
only for a filesystem containing WAL? |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
--ELM1033070448-26881-0_ |
|
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|
|
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--ELM1033070448-26881-0_-- |
|
From [email protected] Thu Sep 26 16:42:13 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
|
by postgresql.org (Postfix) with ESMTP |
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id 5B9B147676D; Thu, 26 Sep 2002 16:42:12 -0400 (EDT) |
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|
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|
To: Bruce Momjian <[email protected]> |
|
Cc: [email protected], |
|
[email protected], [email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <[email protected]> |
|
From: Neil Conway <[email protected]> |
|
In-Reply-To: <[email protected]> |
|
Date: 26 Sep 2002 16:41:49 -0400 |
|
Message-ID: <[email protected]> |
|
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|
|
Bruce Momjian <[email protected]> writes: |
|
> The paper does recommend ext3, but the differences between file systems |
|
> are very small. |
|
|
|
Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
the results I found were drastically different: ext2 was significantly |
|
faster (~50%) than ext3-writeback, which was in turn significantly |
|
faster (~25%) than ext3-ordered. |
|
|
|
> Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> similar to ext2. |
|
|
|
Why would that be? |
|
|
|
Cheers, |
|
|
|
Neil |
|
|
|
-- |
|
Neil Conway <[email protected]> || PGP Key ID: DB3C29FC |
|
|
|
|
|
From [email protected] Thu Sep 26 16:46:10 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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|
Thu, 26 Sep 2002 16:45:55 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <[email protected]> |
|
To: Neil Conway <[email protected]> |
|
Date: Thu, 26 Sep 2002 16:45:54 -0400 (EDT) |
|
Cc: [email protected], |
|
[email protected], [email protected] |
|
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|
|
Neil Conway wrote: |
|
> Bruce Momjian <[email protected]> writes: |
|
> > The paper does recommend ext3, but the differences between file systems |
|
> > are very small. |
|
> |
|
> Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
> the results I found were drastically different: ext2 was significantly |
|
> faster (~50%) than ext3-writeback, which was in turn significantly |
|
> faster (~25%) than ext3-ordered. |
|
|
|
Wow. That leaves no good Linux file system alternatives. PostgreSQL |
|
just wants an ordinary file system that has reliable recovery from a |
|
crash. |
|
|
|
> > Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> > similar to ext2. |
|
> |
|
> Why would that be? |
|
|
|
I assumed it was the double fsync for the normal and journal that made |
|
the journalling file systems slog. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 16:50:43 2002 |
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To: Neil Conway <[email protected]>, [email protected] |
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Subject: Re: [GENERAL] Performance while loading data and indexing |
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References: <[email protected]> |
|
<[email protected]> |
|
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|
I have seen various benchmarks where XFS seems to perform best when it |
|
comes to huge amounts of data and many files (due to balanced internal |
|
b+ trees). |
|
also, XFS seems to be VERY mature and very stable. |
|
ext2/3 don't seem to be that fast in most of the benchmarks. |
|
|
|
i did some testing with reiser some time ago. the problem is that it |
|
seems to restore a very historic consistent snapshot of the data. XFS |
|
seems to be much better in this respect. |
|
|
|
i have not tested JFS yet (but on this damn AIX beside me) |
|
from my point of view i strongly recommend XFS (maybe somebody from |
|
RedHat should think about it). |
|
|
|
Hans |
|
|
|
|
|
Neil Conway wrote: |
|
|
|
>Bruce Momjian <[email protected]> writes: |
|
> |
|
> |
|
>>The paper does recommend ext3, but the differences between file systems |
|
>>are very small. |
|
>> |
|
>> |
|
> |
|
>Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
>the results I found were drastically different: ext2 was significantly |
|
>faster (~50%) than ext3-writeback, which was in turn significantly |
|
>faster (~25%) than ext3-ordered. |
|
> |
|
> |
|
> |
|
>>Also, though ext3 is slower, turning fsync off should make ext3 function |
|
>>similar to ext2. |
|
>> |
|
>> |
|
> |
|
>Why would that be? |
|
> |
|
>Cheers, |
|
> |
|
>Neil |
|
> |
|
> |
|
> |
|
|
|
|
|
-- |
|
*Cybertec Geschwinde u Schoenig* |
|
Ludo-Hartmannplatz 1/14, A-1160 Vienna, Austria |
|
Tel: +43/1/913 68 09; +43/664/233 90 75 |
|
www.postgresql.at <http://www.postgresql.at>, cluster.postgresql.at |
|
<http://cluster.postgresql.at>, www.cybertec.at |
|
<http://www.cybertec.at>, kernel.cybertec.at <http://kernel.cybertec.at> |
|
|
|
|
|
From [email protected] Thu Sep 26 16:57:22 2002 |
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Thu, 26 Sep 2002 16:57:03 -0400 (EDT) |
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From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262057.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <871[email protected]> |
|
To: Neil Conway <[email protected]> |
|
Date: Thu, 26 Sep 2002 16:57:03 -0400 (EDT) |
|
Cc: [email protected].in, |
|
[email protected], [email protected] |
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|
|
Neil Conway wrote: |
|
> Bruce Momjian <[email protected]> writes: |
|
> > The paper does recommend ext3, but the differences between file systems |
|
> > are very small. |
|
> |
|
> Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
> the results I found were drastically different: ext2 was significantly |
|
> faster (~50%) than ext3-writeback, which was in turn significantly |
|
> faster (~25%) than ext3-ordered. |
|
> |
|
> > Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> > similar to ext2. |
|
> |
|
> Why would that be? |
|
|
|
OK, I changed the text to: |
|
|
|
File system choice is particularly difficult on Linux because there are |
|
so many file system choices, and none of them are optimal: ext2 is not |
|
entirely crash-safe, ext3, xfs, and jfs are journal-based, and Reiser is |
|
optimized for small files and does journalling. The journalling file |
|
systems can be significantly slower than ext2 but when crash recovery is |
|
required, ext2 isn't an option. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 17:03:41 2002 |
|
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To: Bruce Momjian <[email protected]> |
|
Cc: Neil Conway <[email protected]>, |
|
[email protected], [email protected], |
|
[email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <[email protected]> |
|
From: Neil Conway <[email protected]> |
|
In-Reply-To: <[email protected]> |
|
Date: 26 Sep 2002 17:03:26 -0400 |
|
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|
|
Bruce Momjian <[email protected]> writes: |
|
> Wow. That leaves no good Linux file system alternatives. |
|
> PostgreSQL just wants an ordinary file system that has reliable |
|
> recovery from a crash. |
|
|
|
I'm not really familiar with the reasoning behind ext2's reputation as |
|
recovering poorly from crashes; if we fsync a WAL record to disk |
|
before we lose power, can't we recover reliably, even with ext2? |
|
|
|
> > > Also, though ext3 is slower, turning fsync off should make ext3 |
|
> > > function similar to ext2. |
|
> > |
|
> > Why would that be? |
|
> |
|
> I assumed it was the double fsync for the normal and journal that |
|
> made the journalling file systems slog. |
|
|
|
Well, a journalling file system would need to write a journal entry |
|
and flush that to disk, even if fsync is disabled -- whereas without |
|
fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that |
|
the performance advantage of ext2 over ext3 is should be even larger |
|
when fsync is not enabled. |
|
|
|
Cheers, |
|
|
|
Neil |
|
|
|
-- |
|
Neil Conway <[email protected]> || PGP Key ID: DB3C29FC |
|
|
|
|
|
From [email protected] Thu Sep 26 17:04:07 2002 |
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Subject: Re: [GENERAL] Performance while loading data and indexing |
|
From: Greg Copeland <[email protected]> |
|
To: [email protected] |
|
Cc: PostgresSQL Hackers Mailing List <[email protected]> |
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In-Reply-To: <[email protected]> |
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References: <[email protected]> |
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<[email protected]> <[email protected]> |
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I tend to agree with this though I have nothing to back up it with. My |
|
impression is that XFS does very well for large files. Accepting that |
|
as fact?, my impression is that XFS historically does well for |
|
database's. Again, I have nothing to back that up other than hear-say |
|
and conjecture. |
|
|
|
Greg |
|
|
|
|
|
On Thu, 2002-09-26 at 15:55, Hans-J=FCrgen Sch=F6nig wrote: |
|
> I have seen various benchmarks where XFS seems to perform best when it=20 |
|
> comes to huge amounts of data and many files (due to balanced internal=20 |
|
> b+ trees). |
|
> also, XFS seems to be VERY mature and very stable. |
|
> ext2/3 don't seem to be that fast in most of the benchmarks. |
|
>=20 |
|
> i did some testing with reiser some time ago. the problem is that it=20 |
|
> seems to restore a very historic consistent snapshot of the data. XFS=20 |
|
> seems to be much better in this respect. |
|
>=20 |
|
> i have not tested JFS yet (but on this damn AIX beside me) |
|
> from my point of view i strongly recommend XFS (maybe somebody from=20 |
|
> RedHat should think about it). |
|
>=20 |
|
> Hans |
|
>=20 |
|
>=20 |
|
> Neil Conway wrote: |
|
>=20 |
|
> >Bruce Momjian <[email protected]> writes: |
|
> >=20=20 |
|
> > |
|
> >>The paper does recommend ext3, but the differences between file systems |
|
> >>are very small. |
|
> >>=20=20=20=20 |
|
> >> |
|
> > |
|
> >Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
> >the results I found were drastically different: ext2 was significantly |
|
> >faster (~50%) than ext3-writeback, which was in turn significantly |
|
> >faster (~25%) than ext3-ordered. |
|
> > |
|
> >=20=20 |
|
> > |
|
> >>Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> >>similar to ext2. |
|
> >>=20=20=20=20 |
|
> >> |
|
> > |
|
> >Why would that be? |
|
> > |
|
> >Cheers, |
|
> > |
|
> >Neil |
|
> > |
|
> >=20=20 |
|
> > |
|
>=20 |
|
>=20 |
|
> --=20 |
|
> *Cybertec Geschwinde u Schoenig* |
|
> Ludo-Hartmannplatz 1/14, A-1160 Vienna, Austria |
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> Tel: +43/1/913 68 09; +43/664/233 90 75 |
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> www.postgresql.at <http://www.postgresql.at>, cluster.postgresql.at=20 |
|
> <http://cluster.postgresql.at>, www.cybertec.at=20 |
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> <http://www.cybertec.at>, kernel.cybertec.at <http://kernel.cybertec.at> |
|
>=20 |
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>=20 |
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From: "James Maes" <[email protected]> |
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To: "Bruce Momjian" <[email protected]>, |
|
"Neil Conway" <[email protected]> |
|
Cc: <[email protected]>, |
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<[email protected]>, <[email protected]> |
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Subject: Re: [GENERAL] Performance while loading data and indexing |
|
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Has there been any thought of providing RAW disk support to bypass the fs? |
|
|
|
-----Original Message----- |
|
From: [email protected] |
|
[mailto:[email protected]]On Behalf Of Bruce Momjian |
|
Sent: Thursday, September 26, 2002 3:57 PM |
|
To: Neil Conway |
|
Cc: [email protected]; [email protected]; |
|
[email protected] |
|
Subject: Re: [HACKERS] [GENERAL] Performance while loading data and |
|
indexing |
|
|
|
|
|
Neil Conway wrote: |
|
> Bruce Momjian <[email protected]> writes: |
|
> > The paper does recommend ext3, but the differences between file systems |
|
> > are very small. |
|
> |
|
> Well, I only did a very rough benchmark (a few runs of pgbench), but |
|
> the results I found were drastically different: ext2 was significantly |
|
> faster (~50%) than ext3-writeback, which was in turn significantly |
|
> faster (~25%) than ext3-ordered. |
|
> |
|
> > Also, though ext3 is slower, turning fsync off should make ext3 function |
|
> > similar to ext2. |
|
> |
|
> Why would that be? |
|
|
|
OK, I changed the text to: |
|
|
|
File system choice is particularly difficult on Linux because there are |
|
so many file system choices, and none of them are optimal: ext2 is not |
|
entirely crash-safe, ext3, xfs, and jfs are journal-based, and Reiser is |
|
optimized for small files and does journalling. The journalling file |
|
systems can be significantly slower than ext2 but when crash recovery is |
|
required, ext2 isn't an option. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
---------------------------(end of broadcast)--------------------------- |
|
TIP 5: Have you checked our extensive FAQ? |
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From [email protected] Thu Sep 26 17:08:13 2002 |
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Thu, 26 Sep 2002 17:07:57 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262107.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <87[email protected]> |
|
To: Neil Conway <[email protected]> |
|
Date: Thu, 26 Sep 2002 17:07:57 -0400 (EDT) |
|
Cc: [email protected].in, |
|
[email protected], [email protected] |
|
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|
|
Neil Conway wrote: |
|
> Bruce Momjian <[email protected]> writes: |
|
> > Wow. That leaves no good Linux file system alternatives. |
|
> > PostgreSQL just wants an ordinary file system that has reliable |
|
> > recovery from a crash. |
|
> |
|
> I'm not really familiar with the reasoning behind ext2's reputation as |
|
> recovering poorly from crashes; if we fsync a WAL record to disk |
|
> before we lose power, can't we recover reliably, even with ext2? |
|
> |
|
> > > > Also, though ext3 is slower, turning fsync off should make ext3 |
|
> > > > function similar to ext2. |
|
> > > |
|
> > > Why would that be? |
|
> > |
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> > I assumed it was the double fsync for the normal and journal that |
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> > made the journalling file systems slog. |
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> |
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> Well, a journalling file system would need to write a journal entry |
|
> and flush that to disk, even if fsync is disabled -- whereas without |
|
> fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that |
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> the performance advantage of ext2 over ext3 is should be even larger |
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> when fsync is not enabled. |
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|
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Yes, it is still double-writing. I just thought that if that wasn't |
|
happening while the db was waiting for a commit that it wouldn't be too |
|
bad. |
|
|
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Is it just me or do all the Linux file systems seem like they are |
|
lacking something when PostgreSQL is concerned? We just want a UFS-like |
|
file system on Linux and no one has it. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 17:09:32 2002 |
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26 Sep 2002 16:09:07 -0500 |
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(CDT).200209262109[email protected]. |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
From: Greg Copeland <[email protected]> |
|
To: Neil Conway <[email protected]> |
|
Cc: Bruce Momjian <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
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In-Reply-To: <87[email protected]> |
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References: <200209262045.[email protected]> |
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<87[email protected]> |
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Content-Type: multipart/signed; micalg=pgp-sha1; |
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On Thu, 2002-09-26 at 16:03, Neil Conway wrote: |
|
> Bruce Momjian <[email protected]> writes: |
|
> > Wow. That leaves no good Linux file system alternatives. |
|
> > PostgreSQL just wants an ordinary file system that has reliable |
|
> > recovery from a crash. |
|
>=20 |
|
> I'm not really familiar with the reasoning behind ext2's reputation as |
|
> recovering poorly from crashes; if we fsync a WAL record to disk |
|
> before we lose power, can't we recover reliably, even with ext2? |
|
|
|
Well, I have experienced data loss from ext2 before. Also, recovery |
|
from crashes on large file systems take a very, very long time. I can't |
|
imagine anyone running a production database on an ext2 file system |
|
having 10's or even 100's of GB. Ouch. Recovery would take forever!=20 |
|
Even recovery on small file systems (2-8G) can take extended periods of |
|
time. Especially so on IDE systems. Even then manual intervention is |
|
not uncommon. |
|
|
|
While I can't say that x, y or z is the best FS to use on Linux, I can |
|
say that ext2 is probably an exceptionally poor choice from a |
|
reliability and/or uptime perspective. |
|
|
|
Greg |
|
|
|
|
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From [email protected] Thu Sep 26 17:17:43 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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|
To: Greg Copeland <[email protected]> |
|
Cc: Neil Conway <[email protected]>, Bruce Momjian <[email protected]>, |
|
[email protected], |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <[email protected]> |
|
<[email protected]> |
|
<[email protected]> |
|
From: Neil Conway <[email protected]> |
|
In-Reply-To: <[email protected]> |
|
Date: 26 Sep 2002 17:17:30 -0400 |
|
Message-ID: <[email protected]> |
|
Lines: 24 |
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|
|
Greg Copeland <[email protected]> writes: |
|
> On Thu, 2002-09-26 at 16:03, Neil Conway wrote: |
|
> > I'm not really familiar with the reasoning behind ext2's |
|
> > reputation as recovering poorly from crashes; if we fsync a WAL |
|
> > record to disk before we lose power, can't we recover reliably, |
|
> > even with ext2? |
|
> |
|
> Well, I have experienced data loss from ext2 before. Also, recovery |
|
> from crashes on large file systems take a very, very long time. |
|
|
|
Yes, but wouldn't you face exactly the same issues if you ran a |
|
UFS-like filesystem in asynchronous mode? Albeit it's not the default, |
|
but performance in synchronous mode is usually pretty poor. |
|
|
|
The fact that ext2 defaults to asynchronous mode and UFS (at least on |
|
the BSDs) defaults to synchronous mode seems like a total non-issue to |
|
me. Is there any more to the alleged difference in reliability? |
|
|
|
Cheers, |
|
|
|
Neil |
|
|
|
-- |
|
Neil Conway <[email protected]> || PGP Key ID: DB3C29FC |
|
|
|
|
|
From [email protected] Thu Sep 26 17:32:17 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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by postgresql.org (Postfix) with ESMTP |
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by postgresql.org (Postfix) with ESMTP |
|
id 0DC964769AE; Thu, 26 Sep 2002 17:32:15 -0400 (EDT) |
|
Received: from doug by varsoon.wireboard.com with local (Exim 3.35 |
|
id 17ugEl-0006nF-00; Thu, 26 Sep 2002 17:31:55 -0400 |
|
To: Bruce Momjian <[email protected]> |
|
From: Doug McNaught <[email protected]> |
|
Cc: Greg Copeland <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <200209262000.[email protected]> |
|
Date: 26 Sep 2002 17:31:55 -0400 |
|
In-Reply-To: Bruce Momjian's message of "Thu, |
|
26 Sep 2002 16:00:48 -0400 (EDT)" |
|
Message-ID: <[email protected]> |
|
Lines: 24 |
|
User-Agent: Gnus/5.0806 (Gnus v5.8.6) Emacs/20.7 |
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|
|
Bruce Momjian <[email protected]> writes: |
|
|
|
> Can anyone clarify if "data=writeback" is safe for PostgreSQL. |
|
> Specifically, are the data files recovered properly or is this option |
|
> only for a filesystem containing WAL? |
|
|
|
"data=writeback" means that no data is journaled, just metadata (which |
|
is like XFS or Reiser). An fsync() call should still do what it |
|
normally does, commit the writes to disk before returning. |
|
|
|
"data=journal" journals all data and is the slowest and safest. |
|
"data=ordered" writes out data blocks before committing a journal |
|
transaction, which is faster than full data journaling (since data |
|
doesn't get written twice) and almost as safe. "data=writeback" is |
|
noted to keep obsolete data in the case of some crashes (since the |
|
data may not have been written yet) but a completed fsync() should |
|
ensure that the data is valid. |
|
|
|
So I guess I'd probably use data=ordered for an all-on-one-fs |
|
installation, and data=writeback for a WAL-only drive. |
|
|
|
Hope this helps... |
|
|
|
-Doug |
|
|
|
From [email protected] Thu Sep 26 17:32:39 2002 |
|
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Thu, 26 Sep 2002 17:32:01 -0400 (EDT) |
|
To: Neil Conway <[email protected]> |
|
Cc: Bruce Momjian <[email protected]>, |
|
[email protected], [email protected], |
|
[email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-reply-to: <[email protected]> |
|
References: <[email protected]> |
|
<[email protected]> |
|
Comments: In-reply-to Neil Conway <[email protected]> |
|
message dated "26 Sep 2002 17:03:26 -0400" |
|
Date: Thu, 26 Sep 2002 17:32:01 -0400 |
|
Message-ID: <[email protected]> |
|
From: Tom Lane <[email protected]> |
|
X-Virus-Scanned: by AMaViS new-20020517 |
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X-Sequence-Number: 30803 |
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|
|
Neil Conway <[email protected]> writes: |
|
> I'm not really familiar with the reasoning behind ext2's reputation as |
|
> recovering poorly from crashes; if we fsync a WAL record to disk |
|
> before we lose power, can't we recover reliably, even with ext2? |
|
|
|
Up to a point. We do assume that the filesystem won't lose checkpointed |
|
(sync'd) writes to data files. To the extent that the filesystem is |
|
vulnerable to corruption of its own metadata for a file (indirect blocks |
|
or whatever ext2 uses), that's not a completely safe assumption. |
|
|
|
We'd be happiest with a filesystem that journals its own metadata and |
|
not the user data in the file(s). I dunno if there are any. |
|
|
|
Hmm, maybe this is why Oracle likes doing their own filesystem on a raw |
|
device... |
|
|
|
regards, tom lane |
|
|
|
From [email protected] Thu Sep 26 17:37:39 2002 |
|
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|
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|
To: Tom Lane <[email protected]> |
|
From: Doug McNaught <[email protected]> |
|
Cc: Neil Conway <[email protected]>, Bruce Momjian <[email protected]>, |
|
[email protected].in, [email protected], |
|
[email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <200209262045.[email protected]> |
|
<87[email protected]> <12930.1033075921@sss.pgh.pa.us> |
|
Date: 26 Sep 2002 17:37:10 -0400 |
|
In-Reply-To: Tom Lane's message of "Thu, 26 Sep 2002 17:32:01 -0400" |
|
Message-ID: <[email protected]> |
|
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|
|
Tom Lane <[email protected]> writes: |
|
|
|
> We'd be happiest with a filesystem that journals its own metadata and |
|
> not the user data in the file(s). I dunno if there are any. |
|
|
|
ext3 with data=writeback? (See my previous message to Bruce). |
|
|
|
-Doug |
|
|
|
From [email protected] Thu Sep 26 17:39:35 2002 |
|
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Thu, 26 Sep 2002 17:39:14 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262139.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <87[email protected]> |
|
To: Neil Conway <[email protected]> |
|
Date: Thu, 26 Sep 2002 17:39:14 -0400 (EDT) |
|
Cc: Greg Copeland <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
X-Mailer: ELM [version 2.4ME+ PL99 (25)] |
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|
|
Neil Conway wrote: |
|
> Greg Copeland <[email protected]> writes: |
|
> > On Thu, 2002-09-26 at 16:03, Neil Conway wrote: |
|
> > > I'm not really familiar with the reasoning behind ext2's |
|
> > > reputation as recovering poorly from crashes; if we fsync a WAL |
|
> > > record to disk before we lose power, can't we recover reliably, |
|
> > > even with ext2? |
|
> > |
|
> > Well, I have experienced data loss from ext2 before. Also, recovery |
|
> > from crashes on large file systems take a very, very long time. |
|
> |
|
> Yes, but wouldn't you face exactly the same issues if you ran a |
|
> UFS-like filesystem in asynchronous mode? Albeit it's not the default, |
|
> but performance in synchronous mode is usually pretty poor. |
|
|
|
Yes, before UFS had soft updates, the synchronous nature of UFS made it |
|
slower than ext2, but now with soft updates, that performance difference |
|
is gone so you have two files systems, ext2 and ufs, similar peformance, |
|
but one is crash-safe and the other is not. |
|
|
|
And, when comparing the journalling file systems, you have UFS vs. |
|
XFS/ext3/JFS/Reiser, and UFS is faster. The only thing the journalling |
|
file system give you is more rapid reboot, but frankly, if your OS goes |
|
down often enough so that is an issue, you have bigger problems than |
|
fsync time. |
|
|
|
The big problem is that Linux went from non-crash safe right to |
|
crash-safe and reboot quick. We need a middle ground, which is where |
|
UFS/soft updates is. |
|
|
|
> The fact that ext2 defaults to asynchronous mode and UFS (at least on |
|
> the BSDs) defaults to synchronous mode seems like a total non-issue to |
|
> me. Is there any more to the alleged difference in reliability? |
|
|
|
The reliability problem isn't alleged. ext2 developers admits ext2 |
|
isn't 100% crash-safe. They will say it is usually crash-safe, but that |
|
isn't good enough for PostgreSQL. |
|
|
|
I wish I was wrong. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 17:42:05 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
|
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Thu, 26 Sep 2002 17:41:22 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262141.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <[email protected]> |
|
To: Doug McNaught <[email protected]> |
|
Date: Thu, 26 Sep 2002 17:41:22 -0400 (EDT) |
|
Cc: Tom Lane <[email protected]>, Neil Conway <[email protected]>, |
|
[email protected].in, [email protected], |
|
[email protected] |
|
X-Mailer: ELM [version 2.4ME+ PL99 (25)] |
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|
|
Doug McNaught wrote: |
|
> Tom Lane <[email protected]> writes: |
|
> |
|
> > We'd be happiest with a filesystem that journals its own metadata and |
|
> > not the user data in the file(s). I dunno if there are any. |
|
> |
|
> ext3 with data=writeback? (See my previous message to Bruce). |
|
|
|
OK, so that makes ext3 crash safe without lots of overhead? |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 17:45:16 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
|
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|
id 454C542C; Thu, 26 Sep 2002 17:45:15 -0400 (EDT) |
|
Subject: Re: [GENERAL] Performance while loading data and indexing |
|
From: Rod Taylor <[email protected]> |
|
To: Bruce Momjian <[email protected]> |
|
Cc: Neil Conway <[email protected]>, |
|
Greg Copeland <[email protected]>, |
|
[email protected], |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
In-Reply-To: <[email protected]> |
|
References: <[email protected]> |
|
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On Thu, 2002-09-26 at 17:39, Bruce Momjian wrote: |
|
> Neil Conway wrote: |
|
> > Greg Copeland <[email protected]> writes: |
|
> > > On Thu, 2002-09-26 at 16:03, Neil Conway wrote: |
|
> > > > I'm not really familiar with the reasoning behind ext2's |
|
> > > > reputation as recovering poorly from crashes; if we fsync a WAL |
|
> > > > record to disk before we lose power, can't we recover reliably, |
|
> > > > even with ext2? |
|
> > > |
|
> > > Well, I have experienced data loss from ext2 before. Also, recovery |
|
> > > from crashes on large file systems take a very, very long time. |
|
> > |
|
> > Yes, but wouldn't you face exactly the same issues if you ran a |
|
> > UFS-like filesystem in asynchronous mode? Albeit it's not the default, |
|
> > but performance in synchronous mode is usually pretty poor. |
|
> |
|
> Yes, before UFS had soft updates, the synchronous nature of UFS made it |
|
> slower than ext2, but now with soft updates, that performance difference |
|
> is gone so you have two files systems, ext2 and ufs, similar peformance, |
|
> but one is crash-safe and the other is not. |
|
|
|
Note entirely true. ufs is both crash-safe and quick-rebootable. You |
|
do need to fsck at some point, but not prior to mounting it. Any |
|
corrupt blocks are empty, and are easy to avoid. |
|
|
|
Someone just needs to implement a background fsck that will run on a |
|
mounted filesystem. |
|
|
|
-- |
|
Rod Taylor |
|
|
|
|
|
From [email protected] Thu Sep 26 17:48:03 2002 |
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Thu, 26 Sep 2002 17:47:43 -0400 (EDT) |
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From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262147.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <1033076723.27772.4.camel@jester> |
|
To: Rod Taylor <[email protected]> |
|
Date: Thu, 26 Sep 2002 17:47:43 -0400 (EDT) |
|
Cc: Neil Conway <[email protected]>, |
|
Greg Copeland <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
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|
|
Rod Taylor wrote: |
|
> > Yes, before UFS had soft updates, the synchronous nature of UFS made it |
|
> > slower than ext2, but now with soft updates, that performance difference |
|
> > is gone so you have two files systems, ext2 and ufs, similar peformance, |
|
> > but one is crash-safe and the other is not. |
|
> |
|
> Note entirely true. ufs is both crash-safe and quick-rebootable. You |
|
> do need to fsck at some point, but not prior to mounting it. Any |
|
> corrupt blocks are empty, and are easy to avoid. |
|
|
|
I am assuming you need to mount the drive as part of the reboot. Of |
|
course you can boot fast with any file system if you don't have to mount |
|
it. :-) |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Sat Sep 28 13:41:23 2002 |
|
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id 8ECED42C; Thu, 26 Sep 2002 18:03:28 -0400 (EDT) |
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Subject: Re: [HACKERS] Performance while loading data and indexing |
|
From: Rod Taylor <[email protected]> |
|
To: Bruce Momjian <[email protected]> |
|
Cc: Neil Conway <[email protected]>, |
|
Greg Copeland <[email protected]>, |
|
[email protected], |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
In-Reply-To: <[email protected]> |
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References: <[email protected]> |
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|
|
On Thu, 2002-09-26 at 17:47, Bruce Momjian wrote: |
|
> Rod Taylor wrote: |
|
> > > Yes, before UFS had soft updates, the synchronous nature of UFS made it |
|
> > > slower than ext2, but now with soft updates, that performance difference |
|
> > > is gone so you have two files systems, ext2 and ufs, similar peformance, |
|
> > > but one is crash-safe and the other is not. |
|
> > |
|
> > Note entirely true. ufs is both crash-safe and quick-rebootable. You |
|
> > do need to fsck at some point, but not prior to mounting it. Any |
|
> > corrupt blocks are empty, and are easy to avoid. |
|
> |
|
> I am assuming you need to mount the drive as part of the reboot. Of |
|
> course you can boot fast with any file system if you don't have to mount |
|
> it. :-) |
|
|
|
Sorry, poor explanation. |
|
|
|
Background fsck (when implemented) would operate on a currently mounted |
|
(and active) file system. The only reason fsck is required prior to |
|
reboot now is because no-one had done the work. |
|
|
|
http://www.freebsd.org/cgi/man.cgi?query=fsck&sektion=8&manpath=FreeBSD+5.0-current |
|
|
|
See the first paragraph of the above. |
|
-- |
|
Rod Taylor |
|
|
|
|
|
From [email protected] Thu Sep 26 18:05:13 2002 |
|
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Thu, 26 Sep 2002 18:04:52 -0400 (EDT) |
|
From: Bruce Momjian <[email protected]> |
|
Message-Id: <200209262204.[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <1033077816.27772.9.camel@jester> |
|
To: Rod Taylor <[email protected]> |
|
Date: Thu, 26 Sep 2002 18:04:52 -0400 (EDT) |
|
Cc: Neil Conway <[email protected]>, |
|
Greg Copeland <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
X-Mailer: ELM [version 2.4ME+ PL99 (25)] |
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|
|
Rod Taylor wrote: |
|
> On Thu, 2002-09-26 at 17:47, Bruce Momjian wrote: |
|
> > Rod Taylor wrote: |
|
> > > > Yes, before UFS had soft updates, the synchronous nature of UFS made it |
|
> > > > slower than ext2, but now with soft updates, that performance difference |
|
> > > > is gone so you have two files systems, ext2 and ufs, similar peformance, |
|
> > > > but one is crash-safe and the other is not. |
|
> > > |
|
> > > Note entirely true. ufs is both crash-safe and quick-rebootable. You |
|
> > > do need to fsck at some point, but not prior to mounting it. Any |
|
> > > corrupt blocks are empty, and are easy to avoid. |
|
> > |
|
> > I am assuming you need to mount the drive as part of the reboot. Of |
|
> > course you can boot fast with any file system if you don't have to mount |
|
> > it. :-) |
|
> |
|
> Sorry, poor explanation. |
|
> |
|
> Background fsck (when implemented) would operate on a currently mounted |
|
> (and active) file system. The only reason fsck is required prior to |
|
> reboot now is because no-one had done the work. |
|
> |
|
> http://www.freebsd.org/cgi/man.cgi?query=fsck&sektion=8&manpath=FreeBSD+5.0-current |
|
> |
|
> See the first paragraph of the above. |
|
|
|
Oh, yes, I have heard of that missing feature. |
|
|
|
-- |
|
Bruce Momjian | http://candle.pha.pa.us |
|
[email protected] | (610) 359-1001 |
|
+ If your life is a hard drive, | 13 Roberts Road |
|
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073 |
|
|
|
From [email protected] Thu Sep 26 19:26:22 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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id 625C74763DD; Thu, 26 Sep 2002 19:26:21 -0400 (EDT) |
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|
Received: from doug by varsoon.wireboard.com with local (Exim 3.35 #1) |
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id 17ui1D-0006sX-00; Thu, 26 Sep 2002 19:26:03 -0400 |
|
To: Bruce Momjian <[email protected]> |
|
From: Doug McNaught <[email protected]> |
|
Cc: Tom Lane <[email protected]>, Neil Conway <[email protected]>, |
|
[email protected], [email protected], |
|
[email protected] |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
References: <[email protected]> |
|
Date: 26 Sep 2002 19:26:03 -0400 |
|
In-Reply-To: Bruce Momjian's message of "Thu, |
|
26 Sep 2002 17:41:22 -0400 (EDT)" |
|
Message-ID: <[email protected]> |
|
Lines: 23 |
|
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|
|
Bruce Momjian <[email protected]> writes: |
|
|
|
> Doug McNaught wrote: |
|
> > Tom Lane <[email protected]> writes: |
|
> > |
|
> > > We'd be happiest with a filesystem that journals its own metadata and |
|
> > > not the user data in the file(s). I dunno if there are any. |
|
> > |
|
> > ext3 with data=writeback? (See my previous message to Bruce). |
|
> |
|
> OK, so that makes ext3 crash safe without lots of overhead? |
|
|
|
Metadata is journaled so you shouldn't lose data blocks or directory |
|
entries. Some data blocks (that haven't been fsync()'ed) may have old |
|
or wrong data in them, but I think that's the same as ufs, right? And |
|
WAL replay should take care of that. |
|
|
|
It'd be very interesting to do some tests of the various journaling |
|
modes. I have an old K6 that I might be able to turn into a |
|
hit-the-reset-switch-at-ramdom-times machine. What kind of tests |
|
should be run? |
|
|
|
-Doug |
|
|
|
From [email protected] Thu Sep 26 22:53:21 2002 |
|
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Date: Fri, 27 Sep 2002 10:55:10 +0800 |
|
From: Yusuf Goolamabbas <[email protected]> |
|
To: [email protected] |
|
Subject: Would ext3 data=journal help for Postgres synchronous io mode |
|
Message-ID: <20020927025510.[email protected]> |
|
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|
|
According to ext3 hackers (Stephen Tweedie, Andrew Morton). ext3 |
|
data=journal mode is much faster than any of the other mode for |
|
workloads which do a lot of syncrhonous i/o. Personally, I have seen |
|
dramatic improvements on moving mail queues to this mode (postfix in |
|
particularly flies with this mode) |
|
|
|
While this may seem contradictory (forcing journaling for the data in |
|
addition to the metadata), it will likely improve the performance for |
|
sync I/O loads like mail servers because it can do all of the I/O to the |
|
journal without any seek or sync overhead while the mail is arriving. |
|
|
|
I assume that since Postgresql does a lot of fsyncs, it would benefit |
|
also. I have sent email to Sridhar asking if he could test this |
|
|
|
Another thing to note is that Linux 2.4.x kernels < 2.4.20-pre4 use |
|
bounce buffer's to do IO if the machine has > 1GB memory. Distributor |
|
kernels such as Redhat/Suse/Mandrake are patched to do IO via DMA |
|
to/from highmem (>1GB). According to IBM's paper @ OLS, this improves IO |
|
performance by 40% |
|
|
|
BTW, Is this list archived on the website |
|
|
|
Regards, Yusuf |
|
-- |
|
Yusuf Goolamabbas |
|
[email protected] |
|
|
|
From [email protected] Thu Sep 26 23:08:32 2002 |
|
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Thu, 26 Sep 2002 23:07:45 -0400 (EDT) |
|
To: Doug McNaught <[email protected]> |
|
Cc: Bruce Momjian <[email protected]>, |
|
Greg Copeland <[email protected]>, |
|
[email protected].in, |
|
PostgresSQL Hackers Mailing List <[email protected]>, |
|
PostgresSQL General Mailing List <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-reply-to: <[email protected]> |
|
References: <200209262000.[email protected]> |
|
<[email protected]> |
|
Comments: In-reply-to Doug McNaught <[email protected]> |
|
message dated "26 Sep 2002 17:31:55 -0400" |
|
Date: Thu, 26 Sep 2002 23:07:44 -0400 |
|
Message-ID: <20359.1033096064@sss.pgh.pa.us> |
|
From: Tom Lane <[email protected]> |
|
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|
|
Doug McNaught <[email protected]> writes: |
|
> "data=writeback" means that no data is journaled, just metadata (which |
|
> is like XFS or Reiser). An fsync() call should still do what it |
|
> normally does, commit the writes to disk before returning. |
|
> "data=journal" journals all data and is the slowest and safest. |
|
> "data=ordered" writes out data blocks before committing a journal |
|
> transaction, which is faster than full data journaling (since data |
|
> doesn't get written twice) and almost as safe. "data=writeback" is |
|
> noted to keep obsolete data in the case of some crashes (since the |
|
> data may not have been written yet) but a completed fsync() should |
|
> ensure that the data is valid. |
|
|
|
Thanks for the explanation. |
|
|
|
> So I guess I'd probably use data=ordered for an all-on-one-fs |
|
> installation, and data=writeback for a WAL-only drive. |
|
|
|
Actually I think the ideal thing for Postgres would be data=writeback |
|
for both data and WAL drives. We can handle loss of un-fsync'd data |
|
for ourselves in both cases. |
|
|
|
Of course, if you keep anything besides Postgres data files on a |
|
partition, you'd possibly want the more secure settings. |
|
|
|
regards, tom lane |
|
|
|
From [email protected] Fri Sep 27 01:12:31 2002 |
|
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Date: Fri, 27 Sep 2002 12:14:40 +0700 (NOVST) |
|
From: Yury Bokhoncovich <[email protected]> |
|
To: Bruce Momjian <[email protected]> |
|
Cc: Neil Conway <[email protected]>, <[email protected].in>, |
|
<[email protected]>, <[email protected]> |
|
Subject: Re: [HACKERS] Performance while loading data and indexing |
|
In-Reply-To: <200209262107.[email protected]> |
|
Message-ID: <Pine.LNX.4.44L0.0209271201580.7775-100000@panda.center-f1.ru> |
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|
|
Hello! |
|
|
|
On Thu, 26 Sep 2002, Bruce Momjian wrote: |
|
|
|
> > I'm not really familiar with the reasoning behind ext2's reputation as |
|
> > recovering poorly from crashes; if we fsync a WAL record to disk |
|
|
|
On relatively big volumes ext2 recovery can end up in formatting the fs |
|
under certain cirrumstances.;-) |
|
|
|
> > > I assumed it was the double fsync for the normal and journal that |
|
> > > made the journalling file systems slog. |
|
> > |
|
> > Well, a journalling file system would need to write a journal entry |
|
> > and flush that to disk, even if fsync is disabled -- whereas without |
|
> > fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that |
|
> > the performance advantage of ext2 over ext3 is should be even larger |
|
> > when fsync is not enabled. |
|
> |
|
> Yes, it is still double-writing. I just thought that if that wasn't |
|
> happening while the db was waiting for a commit that it wouldn't be too |
|
> bad. |
|
> |
|
> Is it just me or do all the Linux file systems seem like they are |
|
> lacking something when PostgreSQL is concerned? We just want a UFS-like |
|
> file system on Linux and no one has it. |
|
|
|
mount -o sync an ext2 volume on Linux - and you can get a "UFS-like" fs.:) |
|
mount -o async an FFS volume on FreeBSD - and you can get boost in fs |
|
performance. |
|
Personally me always mount ext2 fs where Pg is living with sync option. |
|
Fsync in pg is off (since 6.3), this way successfully pass thru a few |
|
serious crashes on various systems (mostly on power problems). |
|
If fsync is on in Pg, performance gets so-oh-oh-oh-oh slowly!=) |
|
I just have done upgrade from 2.2 kernel on ext2 to ext3 capable 2.4 one |
|
so I'm planning to do some benchmarking. Roughly saying w/o benchmarks, |
|
the performance have been degraded in 2/3 proportion. |
|
"But better safe then sorry". |
|
|
|
-- |
|
WBR, Yury Bokhoncovich, Senior System Administrator, NOC of F1 Group. |
|
Phone: +7 (3832) 106228, ext.140, E-mail: [email protected]. |
|
Unix is like a wigwam -- no Gates, no Windows, and an Apache inside. |
|
|
|
|
|
|
|
From [email protected] Fri Sep 27 05:42:31 2002 |
|
Received: from localhost (postgresql.org [64.49.215.8]) |
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From: Mats Lofkvist <[email protected]> |
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X-Newsgroups: comp.databases.postgresql.general, |
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comp.databases.postgresql.questions |
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Subject: Re: [HACKERS] Performance while loading data and indexing |
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Date: 27 Sep 2002 12:40:13 +0200 |
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[email protected] (Neil Conway) writes: |
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[snip] |
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> > Well, I have experienced data loss from ext2 before. Also, recovery |
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> > from crashes on large file systems take a very, very long time. |
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> |
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> Yes, but wouldn't you face exactly the same issues if you ran a |
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> UFS-like filesystem in asynchronous mode? Albeit it's not the default, |
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> but performance in synchronous mode is usually pretty poor. |
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> |
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> The fact that ext2 defaults to asynchronous mode and UFS (at least on |
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> the BSDs) defaults to synchronous mode seems like a total non-issue to |
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> me. Is there any more to the alleged difference in reliability? |
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|
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UFS on most unix systems (BSD, solaris etc) defaults to sync |
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metadata, async data which is a mode that is completely missing |
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from ext2 as far as I know. |
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This is why UFS is considered safer than ext2. (Running with |
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'sync' is too slow to be a usable alternative in most cases.) |
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|
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_ |
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Mats Lofkvist |
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[email protected] |
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|
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PS The BSD soft updates yields the safety of the default sync |
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metadata / async data mode while being at least as fast as |
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running fully async. |
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From [email protected] Fri Sep 27 06:49:23 2002 |
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From: Mats Lofkvist <[email protected]> |
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X-Newsgroups: comp.databases.postgresql.general, |
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comp.databases.postgresql.questions |
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Subject: Re: Performance while loading data and indexing |
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Date: 27 Sep 2002 12:49:17 +0200 |
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[email protected].in ("Shridhar Daithankar") writes: |
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[snip] |
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> |
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> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 |
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> setup.. |
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> |
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|
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RAID5 is not the best for performance, especially write performance. |
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If it is software RAID it is even worse :-). |
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(Note also that you need to check that you are not saturating the |
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number of seeks the disks can handle, not just the bandwith.) |
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Striping should be better (combined with mirroring if you need the |
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safety, but with both striping and mirroring you may need multiple |
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SCSI channels). |
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_ |
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Mats Lofkvist |
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[email protected] |
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From [email protected] Fri Sep 27 11:20:38 2002 |
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Date: Fri, 27 Sep 2002 09:16:03 -0600 (MDT) |
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From: "scott.marlowe" <[email protected]> |
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To: Mats Lofkvist <[email protected]> |
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Cc: <[email protected]> |
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Subject: Re: Performance while loading data and indexing |
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In-Reply-To: <[email protected]> |
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On 27 Sep 2002, Mats Lofkvist wrote: |
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|
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> [email protected] ("Shridhar Daithankar") writes: |
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> |
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> [snip] |
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> > |
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> > Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 |
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> > setup.. |
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> > |
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> |
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> RAID5 is not the best for performance, especially write performance. |
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> If it is software RAID it is even worse :-). |
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|
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I take exception to this. RAID5 is a great choice for most folks. |
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|
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1: RAID5 only writes out the parity stripe and data stripe, not all |
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stripes when writing. So, in an 8 disk RAID5 array, writing to a single |
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64 k stripe involves one 64k read (parity stripe) and two 64k writes. |
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|
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On a mirror set, writing to one 64k stripe involves two 64k writes. The |
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difference isn't that great, and in my testing, a large enough RAID5 |
|
provides so much faster read speads by spreading the reads across so many |
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heads as to more than make up for the slightly slower writes. My testing |
|
has shown that a 4 disk RAID5 can generally run about 85% or more the |
|
speed of a mirror set. |
|
|
|
2: Why does EVERYONE have to jump on the bandwagon that software RAID 5 |
|
is bad. My workstation running RH 7.2 uses about 1% of the CPU during |
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very heavy parallel access (i.e. 50 simo pgbenchs) at most. I've seen |
|
many hardware RAID cards that are noticeable slower than my workstation |
|
running software RAID. You do know that hardware RAID is just software |
|
RAID where the processing is done on a seperate CPU on a card, but it's |
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still software doing the work. |
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|
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3: We just had a hardware RAID card mark both drives in a mirror set bad. |
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It wouldn't accept them back, and all the data was gone. poof. That |
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would never happen in Linux's kernel software RAID, I can always make |
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Linux take back a "bad" drive. |
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|
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The only difference between RAID5 with n+1 disks and RAID0 with n disks is |
|
that we have to write a parity stripe in RAID5. It's ability to handle |
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high parallel load is much better than a RAID1 set, and on average, you |
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actually write about the same amount with either RAID1 or RAID5. |
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|
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Don't dog software RAID5, it works and it works well in Linux. Windows, |
|
however, is another issue. There, the software RAID5 is pretty pitiful, |
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both in terms of performance and maintenance. |
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From [email protected] Fri Sep 27 15:01:43 2002 |
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To: [email protected] |
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Subject: Re: [GENERAL] Performance while loading data and indexing |
|
References: <[email protected]> |
|
<[email protected]> <[email protected]> |
|
Mail-Followup-To: [email protected] |
|
From: Florian Weimer <[email protected]> |
|
Date: Fri, 27 Sep 2002 21:01:38 +0200 |
|
In-Reply-To: <[email protected]> (Tom Lane's message of "Thu, |
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26 Sep 2002 17:32:01 -0400") |
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Tom Lane <[email protected]> writes: |
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|
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> We'd be happiest with a filesystem that journals its own metadata and |
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> not the user data in the file(s). I dunno if there are any. |
|
|
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Most journalling file systems work this way. Data journalling is not |
|
very widespread, AFAIK. |
|
|
|
-- |
|
Florian Weimer [email protected] |
|
University of Stuttgart http://CERT.Uni-Stuttgart.DE/people/fw/ |
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RUS-CERT fax +49-711-685-5898 |
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From [email protected] Fri Sep 27 21:46:57 2002 |
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Date: Sat, 28 Sep 2002 13:38:52 +1200 |
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From: Mark Kirkwood <[email protected]> |
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To: "scott.marlowe" <[email protected]> |
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Cc: Mats Lofkvist <[email protected]>, [email protected] |
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Subject: Re: Performance while loading data and indexing |
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scott.marlowe wrote: |
|
|
|
>(snippage) |
|
>I take exception to this. RAID5 is a great choice for most folks. |
|
> |
|
> |
|
I agree - certainly RAID5 *used* to be rather sad, but modern cards have |
|
improved this no end on the hardware side - e.g. |
|
|
|
I recently benchmarked a 3Ware 8x card on a system with 4 x 15000 rpm |
|
Maxtor 70Gb drives and achieved 120 Mb/s for (8K) reads and 60 Mb/s for |
|
(8K) writes using RAID5. I used Redhat 7.3 + ext2. The benchmarking |
|
program was Bonnie. |
|
|
|
Given that the performance of a single disk was ~30 Mb/s for reads and |
|
writes, I felt this was quite a good result ! ( Other cards I had tried |
|
previously struggled to maintain 1/2 the write rate of a single disk in |
|
such a configuration). |
|
|
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As for software RAID5, I have not tried it out. |
|
|
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Of course I could not get 60Mb/s while COPYing data into Postgres... |
|
typically cpu seemed to be the bottleneck in this case (what was the |
|
actual write rate? I hear you asking..err.. cant recall I'm afraid.. |
|
must try it out again ) |
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|
|
cheers |
|
|
|
Mark |
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|
|
|
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From [email protected] Sat Sep 28 11:49:21 2002 |
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Reply-To: "Waruna Geekiyanage" <[email protected]> |
|
From: "Waruna Geekiyanage" <[email protected]> |
|
To: <[email protected]> |
|
Subject: INDEX |
|
Date: Sat, 28 Sep 2002 21:50:13 +0600 |
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|
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When a table is created with a primary key it generates a index. |
|
Dos the queries on that table use that index automatically? |
|
Do I need to reindex that index after insertions? |
|
|
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------=_NextPart_000_0105_01C26739.06687120 |
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Content-Type: text/html; |
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charset="iso-8859-1" |
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
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</HEAD> |
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<BODY bgColor=3D |
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<DIV><FONT face=3DArial size=3D2>When a table is created with a primary key= |
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it=20 |
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generates a index.</FONT></DIV> |
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<DIV><FONT face=3DArial size=3D2>Dos the queries on that table use that ind= |
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ex=20 |
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automatically?</FONT></DIV> |
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<DIV><FONT face=3DArial size=3D2>Do I need to reindex that index after=20 |
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insertions?</FONT></DIV></BODY></HTML> |
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------=_NextPart_000_0105_01C26739.06687120-- |
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From [email protected] Sat Sep 28 15:13:19 2002 |
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for <[email protected]>; Sat, 28 Sep 2002 15:13:18 -0400 |
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Date: Sat, 28 Sep 2002 15:13:18 -0400 |
|
From: Andrew Sullivan <[email protected]> |
|
To: [email protected] |
|
Subject: Re: INDEX |
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Message-ID: <20020928151318.[email protected]> |
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On Sat, Sep 28, 2002 at 09:50:13PM +0600, Waruna Geekiyanage wrote: |
|
> When a table is created with a primary key it generates a index. |
|
> Dos the queries on that table use that index automatically? |
|
|
|
Only if you analyse the table, and it's a "win". See the various |
|
past discussion on -general, for instance, about index use, and the |
|
FAQ. |
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|
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> Do I need to reindex that index after insertions? |
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|
|
No, but you need to analyse. |
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|
|
A |
|
|
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-- |
|
---- |
|
Andrew Sullivan 204-4141 Yonge Street |
|
Liberty RMS Toronto, Ontario Canada |
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<[email protected]> M2P 2A8 |
|
+1 416 646 3304 x110 |
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