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The WebSphere MQ dead-letter queue handler

 

A dead-letter queue (DLQ), sometimes referred to as an undelivered-message queue, is a holding queue for messages that cannot be delivered to their destination queues. Every queue manager in a network should have an associated DLQ.

Messages can be put on the DLQ by queue managers, message channel agents (MCAs), and applications. All messages on the DLQ must be prefixed with a dead-letter header structure, MQDLH.

Messages put on the DLQ by a queue manager or a message channel agent always have an MQDLH; applications putting messages on the DLQ must supply an MQDLH. The Reason field of the MQDLH structure contains a reason code that identifies why the message is on the DLQ.

All WebSphere MQ environments need a routine to process messages on the DLQ regularly. WebSphere MQ supplies a default routine, called the dead-letter queue handler (the DLQ handler), which you invoke using the runmqdlq command.

Instructions for processing messages on the DLQ are supplied to the DLQ handler by means of a user-written rules table. That is, the DLQ handler matches messages on the DLQ against entries in the rules table; when a DLQ message matches an entry in the rules table, the DLQ handler performs the action associated with that entry.

This chapter contains the following sections:

• Invoking the DLQ handler

• The DLQ handler rules table

• How the rules table is processed

• An example DLQ handler rules table

• Invoking the DLQ handler
  

• The DLQ handler rules table
  

• How the rules table is processed
  

• An example DLQ handler rules table
  

 

Parent topic:

Configuring WebSphere MQ

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