Converged Application Server enables you to store long-lived call state data in an Oracle or MySQL RDBMS in order to conserve RAM. When you enable RDBMS persistence, by default the Coherence cache persists a call state's data to the RDBMS after the call dialog has been established, and at subsequent dialog boundaries, retrieving or deleting the persisted call state data as necessary to modify or remove the call state.

Oracle also provides an API for application designers to provide "hints" as to when the Coherence cache should persist call state data. These hints can be used to persist call state data to the RDBMS more frequently, or to disable persistence for certain calls.

Note that Converged Application Server only uses the RDBMS to supplement the Coherence cache's in-memory replication functionality. To improve latency performance when using an RDBMS, the Coherence cache maintains SIP timers in memory, along with call states being actively modified (for example, in response to a new call being set up). Call states are automatically persisted only after a dialog has been established and a call is in progress, at subsequent dialog boundaries, or in response to persistence hints added by the application developer.

When used in conjunction with an RDBMS, the Coherence cache selects one engine to process all call state writes (or deletes) to the database. Any available server can be used to retrieve call states from the persistent store as necessary for subsequent reads.

RDBMS call state storage can be used in combination with an engine cache, if your domain uses a SIP-aware load balancer to manage connections to the engine tier. See "Using the Engine Cache".