For each MDB, application server maintains a pool of its instances based on the configuration done in the Application Server. If number of MDB instances in application server is configured as 5 then 5 instances of MDB is active to fetch messages from the JMS Queue.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: Performance Tuning with respect to Message Queue and Message Driven Beans