The PersistenceManager (PM) is used by a destination to store messages marked as being persistent. JBossMQ has several different implementations of the persistent manager, but only one can be enabled per server instance. You should enable the persistence manager that best matches your requirements.
JDBC2 persistence manager: The JDBC2 persistence manager allows you to store persistent messages to a relational database using JDBC. The performance of this PM is directly related to the performance that can be obtained from the database. This PM has a very low memory overhead compared to the other persistence managers. Furthermore it is also highly integrated with the MessageCache to provide efficient persistence on a system that has a very active MessageCache.
Null Persistence Manager: A wrapper persistence manager that can delegate to a real persistence manager. Configuration on the destinations decide whether persistence and caching is actually performed. The example configuration can be found in docs/examples/jms. To use the null persistence manager backed by a real persistence manager, you need to change the ObjectName of the real persistence manager and link the new name to the null persistence manager.