In this book, incorrect output refers to your application:
If messages do not appear when you are expecting them, check for the following:
If messages are being put or retrieved within syncpoint, they are not available to other tasks until the unit of recovery has been committed.
You can set the wait interval as an option for the MQGET call. Ensure that you are waiting long enough for a response.
Check that you are waiting for a message with the correct MsgId or CorrelId. A successful MQGET call sets both these values to that of the message retrieved, so you might need to reset these values in order to get another message successfully.
Also, check whether you can get other messages from the queue.
If not, and WebSphere MQ has been restarted, the message has been lost.
If you cannot find anything wrong with the queue, and WebSphere MQ is running, check the process that you expected to put the message onto the queue for the following:
If it should have been triggered, check that the correct trigger options were specified.
Look for evidence of an abnormal end in the job log.
If multiple transactions are serving the queue, they can conflict with one another. For example, suppose one transaction issues an MQGET call with a buffer length of zero to find out the length of the message, and then issues a specific MQGET call specifying the MsgId of that message. However, in the meantime, another transaction issues a successful MQGET call for that message, so the first application receives a reason code of MQRC_NO_MSG_AVAILABLE. Applications that are expected to run in a multiple server environment must be designed to cope with this situation.
Consider that the message could have been received, but that your application failed to process it in some way. For example, did an error in the expected format of the message cause your program to reject it? If this is the case, refer to Messages that contain unexpected or corrupted information.
If the information contained in the message is not what your application was expecting, or has been corrupted in some way, consider the following:
Ensure that all changes are simultaneously reflected on all systems that need to be aware of the change.
For example, the format of the message data might have been changed, in which case, both applications must be recompiled to pick up the changes. If one application has not been recompiled, the data will appear corrupt to the other.
Check that the messages your application is receiving are not really intended for an application servicing a different queue. If necessary, change your security definitions to prevent unauthorized applications from putting messages on to the wrong queues.
If your application uses an alias queue, check that the alias points to the correct queue.
Check that your application should have started; or should a different application have started?
If these checks do not enable you to solve the problem, check your application logic, both for the program sending the message, and for the program receiving it.
If your application uses distributed queues, consider the following points:
Check that both systems are available, and connected to WebSphere MQ. Check that the connection between the two systems is active.
You can use the MQSC command PING against either the queue manager (PING QMGR) or the channel (PING CHANNEL) to verify that the link is operable.
Check that triggering is activated in the remote system.
If so, check if the message has been put onto the dead-letter queue.
The dead-letter queue header contains a reason or feedback code explaining why the message could not be put onto the target queue. See the WebSphere MQ Application Programming Reference for information about the dead-letter queue header structure.
For example, the message length could be longer than the receiving queue manager can handle.
For example, a mismatch in sequence number wrap can stop the distributed queuing component. See WebSphere MQ Intercommunication for more information about distributed queuing.
If the data format is not recognized for conversion, the data conversion exit is taken to allow you to perform the translation with your own routines.
Refer to the WebSphere MQ Application Programming Guide for further details of data conversion.
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