You create a message when you use an MQI call to put the message on a queue. As input to the call, you supply some control information in a message descriptor (MQMD) and the data that you want to send to another program. But at the design stage, you need to consider the following questions, because they affect the way that you create your messages:
Do you want your request and reply messages to be synchronous? This implies that you set a timeout period for the reply to answer your request, and if you do not receive the reply within that period, it is treated as an error.
Or would you prefer to work asynchronously, so that your processes do not have to depend upon the occurrence of specific events, such as common timing signals?
Another consideration is whether you have all your messages inside a unit of work.
Programs can also select a message using the identifier that the queue manager assigned when the message was put on the queue. Alternatively, you can generate your own identifiers for each of your messages.
Because messages on shared queues (only available on WebSphere MQ for z/OS) are held in the Coupling Facility (CF), nonpersistent messages are preserved across restarts of a queue manager as long as the CF remains available. If the CF fails, nonpersistent messages are lost.
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