WebSphere Application Server Version 6.1 Feature Pack for Web Services
             Operating Systems: z/OS

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

MDB throttle

On z/OS, the "MDB throttle" is used to control the amount of work that the server processes at a given time for a message-driven bean. The MDB throttle limits how far the message listener port will "read ahead" to try to ensure that the work request queue does not have a backlog of messages to be processed.

The preprocessing, classification, building of and queuing of a work record to prepare for dispatching a specific message-driven bean is a relatively basic operation, especially when compared to the actual business logic of the message-driven bean and the container infrastructure on the application dispatch path. When the rate of messages arriving reaches occasional high volumes, or peaks, the controller can preprocess many more messages than the back-end servants can process by running the associated MDB application. The result of these peaks (in asynchronous work) is that the WLM work request queue becomes backed up waiting for worker threads (in the servants) that have a backlog of messages to be processed.

A backlog of messages to be processed can also occur as a result of situations where the scalable server is taken out of service for a period of time. This causes messages to build up on the JMS destination waiting for the server to restart. When the server does restart, there is a flood of new work introduced into the server.

The MDB throttle limits how far the message listener port will "read ahead" down the JMS queue (or topic), to try to ensure that the work request queue does not have a backlog of messages to be processed.

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Last updated: Nov 25, 2008 2:35:59 AM CST
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