Creating database connections is expensive. You reduce overhead by pooling your database connections. Make sure you call on a connection as soon as possible. When pooling is enabled, calling Closeor Dispose returns the connection to the pool instead of closing the underlying database connection.


You must account for the following issues when pooling is part of your design:

  •  Share connections. Use a per-application or per-group service account to connect to the database. This creates a single pool or a small number of pools, and it enables many client requests to share the same connections.

  •  Avoid per-user logons to the database. Each logon creates a separate pooled connection. This means that you end up with a large number of small pools. If you need a different user for each connection, disable pooling or set a small maximum size for the pool.

  • Do not vary connection strings. Different connection strings generate different connection pools. For example, using different capitalization, extra spaces, or different ordering of attributes causes connections to go to different pools. The SQL Server .NET Data Provider performs a byte-by-byte comparison to determine whether connection strings match.
  •  Release connections. Do not cache connections. For example, do not put them in session or application variables. Close connections as soon as you are finished with them. Busy connections are not pooled.
  •  Passing connections. Do not pass connections between logical or physical application layers.
  •  Consider tuning your pool size if needed. For example, in the case of the .NET Framework Data Provider for SQL Server, the default minimum pool size is zero and the maximum is 100. You might need to increase the minimum size to reduce warm-up time. You might need to increase the maximum size if your application needs more than 100 connections.
  • Connection pools are managed by the specific database provider. SqlClient, OleDB client, and third-party clients may provide different configuration and monitoring options.

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