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Multi-tenant applications are not rare in the cloud since all applications that offer the same services to several different users are often implemented as multi-tenant applications, where each tenant corresponds to a user subscription. Accordingly, relational databases, such as Azure SQL Server, are conceived to work in the cloud and usually offer sharding options for multi-tenant applications. Typically, sharding is not a cloud service and must be defined with database engine commands. Here, we will not describe how to define shards with Azure SQL Server, but the Further reading section contains a link to the official Microsoft documentation. The following table presents the pros and cons of each database approach:
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Subject
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SQL
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NoSQL document-oriented DB
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Schema
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Easy to deal with in well-structured schemas. Today, it is possible to design hybrid solutions with JSON/XML columns to store unstructured data.
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Preferred when data has almost no predefined structure.
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Performance
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In general, bad performance in distributed environments.
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In general, good performance for reading and writing distributed data.
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Language
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Declarative to query and update data, standard.
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Procedural to query and update operations.
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Consistency
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Strong use of foreign keys.
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Weak and left to the developer's decision. All related objects that are likely to be processed together into a single entry.
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Transactions
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Supported.
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By default, they are not supported.
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Scale
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Vertically upgrading hardware.
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Horizontally with data sharding.
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Table 12.1: Pros and cons for each database approach
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In conclusion, relational databases offer a pure, logical view of data that is independent of the way they are stored and use declarative language to query and update them. This simplifies development and system maintenance, but it may cause performance issues in a distributed environment that requires write scale-out. It is also worth noting that tools like Entity Framework, presented in Chapter 13, Interacting with Data in C# – Entity Framework Core, help in bridging the gap between objects and relational data, making development more intuitive for relational databases.
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In NoSQL document-oriented databases, you must handle more details about how to store data, as well as some procedural details for all the update and query operations, manually, but this allows you to optimize performance in distributed environments that require both read and write scale-out. On the flip side, working with NoSQL data, especially when it involves deserializing formats like JSON or XML, can be tricky. It often requires careful mapping to ensure data integrity, which can be both challenging and error-prone. In the next section, we will look at Azure Cosmos DB, the main Azure NoSQL offering, which, fortunately, can be integrated with Entity Framework for a more streamlined development experience.
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Azure Cosmos DB – an opportunity to manage a multi-continental database
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Azure Cosmos DB is Azure’s main NoSQL offering. Azure Cosmos DB has its own interface that is a subset of SQL, but it can be configured with a MongoDB interface, a Table API, or a Cassandra API. It can also be configured as a graph data model that can be queried with Gremlin.
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You can find further details about Cosmos DB in the official documentation: https://docs.microsoft.com/en-us/azure/cosmos-db/.
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Cosmos DB allows replication for fault tolerance and read scale-out, and replicas can be distributed geographically to optimize communication performance. Moreover, you can specify which data center all the replicas are placed in. The user also has the option to write-enable all the replicas so that writes are immediately available in the geographical area where they are done. Write scale-up is achieved with sharding, which the user can configure by defining which properties to use as shard keys.
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Creating an Azure Cosmos DB account
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You can define a Cosmos DB account by typing Cosmos DB into the Azure portal search bar and clicking + Create. The following page will appear:
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Figure 12.5: Creating an Azure Cosmos DB account
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For instance, if you select the Core (SQL) option, the account name you choose is used in the resource URI as {account_name}.documents.azure.com. Then, you can decide which location the main database will be placed in and the capacity mode. You can check more information about the capacity modes available at https://docs.microsoft.com/en-us/azure/cosmos-db/throughput-serverless.
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Microsoft keeps improving many of its Azure services. The best way to keep updated about new features of any Azure component is by checking its documentation from time to time.
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On the Global Distribution tab, the Multi-region Writes toggle lets you enable writes on geographically distributed replicas. If you do not do this, all write operations will be routed to the main location. Finally, you may also define network connectivity, backup policies, and encryption during the creation process.
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Creating an Azure Cosmos DB container
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Once you have created your Azure Cosmos DB – Core SQL account, select Data Explorer to create your databases and containers inside of them. A container is the unit of scalability both for provisioned throughput and storage, available when you decide by provisioned throughput capacity mode.
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