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# CMP and External Transactions

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In general, the transaction isolation information in this section applies to both CMP and non-CMP applications, with the following exception:

For application servers other than OC4J, when using a TopLink application with CMP, Oracle recommends that you configure your container to use separate read and write connection pools, and to associate only the write connections with an external transaction. This means the read connections do not participate in the transaction.

Note: OC4J always uses the same connection pool for reading and writing: it uses JTA connections from that pool for writing, and non-JTA connections from the pool for reading.

However, because TopLink treats EJB finders as just another type of query, you can use your descriptor configuration to exploit the options described in "Reading Through the Write Connection". For example, if you configure a descriptor to use pessimistic locking (see "Configuring Locking Policy"), then when its finder is invoked it will allocate a write connection early and both read and write operations will use the same connection.

Refer to "Externally Managed Transactional Data Sources" for more information on external transactions with transactional data sources.