The message-driven bean throttling mechanism on z/OS
On z/OS , message-driven bean throttling mechanisms control the amount of work that the server processes at any given time for a message-driven bean. The throttling mechanism limits how far the listener will read ahead to try to ensure that the work request queue does not have a backlog of messages to be processed.
Figure 1. Controlling processing of the WMQ queue and WLM queues
The MDB throttling mechanism is needed because the preprocessing, classification, building, and queuing of a work record to prepare for the dispatch of a message-driven bean is a simple operation, when compared with the business logic of the message-driven bean and the container infrastructure on the application dispatch path. This means that, when messages arrive at the WMQ queue at a high rate, the controller can preprocesses the messages faster than the message-driven bean application running in the servant regions. Peaks in asynchronous work cause a build up of messages in the workload management (WLM) work request queue, because these messages are waiting for worker threads in the servants that have a backlog of messages to be processed. For example, a backlog of messages to be processed can occur when a scalable server is taken out of service. Messages build up on the JMS destination waiting for the server to restart. When the server does restart, a flood of new work is introduced into the server.
To avoid a backlog of messages on the WLM work request queue, the message-driven bean throttling mechanism limits how far the message listener port canread ahead down the JMS queue or topic.
Related concepts
(zos) Tune listener ports for workload management on WebSphere Application Server for z/OS
(zos) MDB throttle settings for message-driven beans on z/OS