This topic applies only on the z/OS operating system.

Message Listener Service on z/OS

On the z/OS platform, the Message Listener Service implementation exploits the scalable server architecture provided by WebSphere Application Server for z/OS, by dividing the listener port functionality across the controller and servant processes.

A single message listener is registered in the controller portion of the ListenerPort, while application dispatch (that is, dispatch of the user application's onMessage(Message) EJB method) is then spread across the various servants comprising the server. This implementation is referred to as "listening in the controller" for the message-driven bean messages.

Note: An important point to note is that the WebSphere Application Server for z/OS Message Listener Service implementation does not use the just-described "listening in the controller" internal configuration in all cases, but rather only in the cases in which the message-driven bean is mapped to a queue (that is, listening on a Queue) or mapped (listening) to a topic through a durable subscription.

In the case in which the message-driven bean is listening to a topic through a nondurable subscription, the listener port registers a listener in each servant, rather than registering a single listener in the controller.

For a topic on which a message-driven bean is listening through a non-durable subscription, a single message published to that topic is dispatched once for each servant comprising the server. In contrast, if a message-driven bean is listening on a queue, or a topic through a durable subscription, a single message sent is dispatched once only, to a single servant, for the entire server.

The configuration of the listener port, in the "listening in the controller" case, is administered externally through the controls described in Tuning MDB processing on z/OS and Concepts and considerations for MDB settings on z/OS.

For a non-durable subscription message-driven bean, which is listening in each servant as described above, the listener ports are configured in the same manner as they are on distributed platforms. The single set of settings configured for the listener port are applied identically to each servant in this case.




Related tasks
Configuring the message listener service
Related reference
Message listener service
Reference topic    

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