Question

How to handle messages bigger than 4MB on z/OS? I can’t use segmentation, because it is not supported on z/OS.

Some OS have even bigger limits measured even in kB.

What is the common approach in this case?

Answer 1

You are not hitting a z/OS limit but rather the default maximum message length on WebSphere MQ. Note that the Infocenter says “On z/OS, specify a value in the range zero through 100 MB (104 857 600 bytes)”.

To fix this, change the MAXMSGL on any queues and channels through which the message might pass. Don’t forget to update the Dead Letter Queue’s MAXMSGL as well as transmission queues.

Be aware that MAXMSGL is there to save you! Many people set the value to its highest possible size and then run out of disk space. If the application hits a soft limit such as MAXMSGL or MAXDEPTH the effect is limited and generally recoverable. If the disk space is exhausted, the entire QMgr comes to a screeching halt and all connected apps are impacted.

For more on this, please see the Mice and Elephants article on developerWorks.

UDATE:
Update based on comments asking about specifics of HP NonStop and WMQ V5.3.

Please see the WMQ V5.3 manuals available in the WMQ Documentation library. The second link is the System Administration Guide for WMQ V5.3 on HP NonStop. Message lengths are discussed on P4:

The default maximum message length is 4 MB, although you can increase
this to a maximum length of 100 MB (where 1 MB equals 1 048 576
bytes). In practice, the message length might be limited by:

• The maximum message length defined for the receiving queue
• The maximum message length defined for the queue manager
• The maximum message length defined by the queue
• The maximum message length defined by either the sending or receiving application
• The amount of storage available for the message

So there’s no arbitrarily small max message length on HP NonStop or associated with V5.3 of WMQ.