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babu_murugesan · Posted: Wed Nov 22, 2006 8:56 am Post subject: Message reading

Assume;

Up to 2000 concurrent users to be supported.
MQ listener program written in COBOL, started by CICS when message arrives in an initiation queue.

Message reading
Our current messaging system via APPC on LU6.2 receives the message in chunks dynamically allocating memory to store it as required.
It looks as if with MQ we read the entire message at once. This means that we will have to statically allocate the maximum possible amount of memory required for a message in our MQ listener program. (The MQ listener is triggered from the initiation queue for every new message).
This means that every CICS transaction will have lots of potentially redundant memory allocated for it, for the duration of the MQ listener transaction.
At what sort of maximum message size would this become a problem ?

One possible way around this would be to have different types of message written to different request queues and inquire on the queue before we read the message to get the maximum message length for that queue. Memory would then be allocated dynamically for that maximum size.
Is this a viable solution ?

Alternatively, if we read a message then discover it is too long for our receiving variable, we could allocate more memory then try and read it again. Is there any guarantee that we can re-read the same message ? Can it be â€˜lockedâ€™ to prevent another process reading it (without performance implications?)

Thanks,
Babu M