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# Connection Pools

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A connection pool is a service that creates and maintains a shared collection (pool) of data source connections on behalf of one or more clients. The connection pool provides a connection to a process on request, and returns the connection to the pool when the process is finished using it. When it is returned to the pool, the connection is available for other processes. Because establishing a connection to a data source can be time-consuming, reusing such connections in a connection pool can improve performance.

TopLink uses connection pools to manage and share the connections used by server and client sessions. This feature reduces the number of connections required and allows your application to support many clients.

You can configure your session to use internal connection pools provided by TopLink or external connection pools provided by a JDBC driver or J2EE container.

You can use connection pools in your TopLink application for a variety of purposes, such as reading, writing, sequencing, and other application-specific functions.

This section describes the following:

- Internal Connection Pools

- External Connection Pools

- Default (Write) and Read Connection Pools

- Sequence Connection Pools

- Application-Specific Connection Pools