The container for message-driven beans (MDB) is different than the containers for entity and session beans. In the MDB container, sessions and threads are attached to the beans in the MDB pool. This design makes it possible to pool the threads for executing message-driven requests in the container.
Tune the Message-Driven bean’s pool size to optimize the concurrent processing of messages. Set the size of the MDB pool to, based on all the parameters of the server (taking other applications into account). For example, a value greater than 500 is generally too large.
You can configure MDB pool settings in the Admin Console at Configurations > config-name > EJB Container (MDB Settings). You can also set it with asadmin as follows:
asadmin set server.mdb-container.max-pool-size = value