2 MDB Life Cycle

Overview

This section describes the phases in the life cycle of a message-driven bean instance.

MDBs and Concurrent Processing

MDBs support concurrent processing for both topics and queues. For more information about topics and queues, see MDBs and Messaging Models.

WebLogic Server maintains a free pool where MDB instances that are not currently servicing requests reside.The number of MDB instances in the free pool is controlled by the value of the max-beans-in-free-pool attribute, the number of available threads in the thread pool, the type of thread pool, and sometimes other factors. See "Tuning Message-Driven Beans" in Oracle Fusion Middleware Performance and Tuning for Oracle WebLogic Server.

Each MDB that is deployed to a server instance creates a single JMS connection.

In a queue-based JMS application (point-to-point model), each MDB instance has its own session.

In a topic-based JMS application (the publish/subscribe model), all local instances of an MDB share a JMS session. A given message is distributed to multiple MDBs—one copy to each subscribing MDB. If multiple MDBs are deployed to listen on the same topic, then each MDB receives a copy of every message. A message is processed by one instance of each MDB that listens to the topic.

Limitations for Multi-threaded Topic MDBs

The default behavior for non-transactional topic MDBs is to multi-thread the message processing. In this situation, the MDB container fails to provide reproducible behavior when the topic is not a WebLogic JMS Topic, such as unexpected exceptions and acknowledgement of messages that have not yet been processed. For example, if an application throws RuntimeException from onmessage, the container may still acknowledges the message.

Oracle recommends setting max-beans-in-free-pool to a value of 1 in the deployment descriptor to prevent multi-threading in topic MDBs when the topic is a foreign vendor topic (not a WebLogic JMS topic).