Dead Letter Queue handler (runmqdlq)
This section looks at the WebSphere MQ Dead Letter Queue (DLQ), what it is, and how to handle messages that are put on this queue.
Firstly, let's look at what a DLQ actually does. In one sentence, a DLQ is a queue that stores messages that cannot be routed to their correct destination(s). This occurs when, for example, the destination queue is full.
In our examples, we always define a DLQ called DEAD.LETTER.QUEUE.<QMgr-name>.
We can check that we have a DLQ defined by displaying the attributes of the Queue Manager. So for Q Apply running on CLP-B, we would issue:
$ runmqsc QMB
: dis qmgrThe output from this command can be seen in the Issuing commands to a Queue Manager (runmqsc)—Displaying the attributes of a Queue Manager section.
To handle messages in the DLQ, we use the WebSphere MQ DLQ message handler utility called runmqdlq. Note that we cannot simply read the messages off the DLQ and put them somewhere else, because then we would change the message...
