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# Externally Managed Transactional Data Sources

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A TopLink transactional data source is externally managed if the connection pool is managed by a transaction service (such as an application server controlled transaction or a JTA transaction). A JTA managed data source or connection pool is commonly used in J2EE applications and normally required in EJB applications. Use an externally-managed connection pool as follows:

- Configure the session to use an `ExternalTransactionController` to integrate TopLink's unit of work with the external transaction service (see "Integrating the Unit of Work With an External Transaction Service").

- Use the external-transaction-control option to specify the connection's login and inform TopLink that the connection is maintained by the external controller (see "Configuring External Connection Pooling").

- You may need to configure the TopLink read connection pool or sequence connection pool to use a non-JTA connection pool in order to avoid transactional overhead (see "Default (Write) and Read Connection Pools").

For more information on transactional data sources, see the following:

- "JTA Controlled Transactions"

- "OTS Controlled Transactions"

- "CMP Controlled Transactions"

Refer to Understanding TopLink Transactions for more information on TopLink transactions.