Syncpoints

The queue management functions used when the queue manager is running operate within a syncpoint so that, if a function fails, its effects can be backed out. The queue manager attribute, MAXUMSGS, specifies the maximum number of messages that a task can get or put within a single unit of recovery.

MAXUMSGS should normally be set to a low value, both to protect against looping applications, and because there might be a very large CPU cost in committing a large number of messages.

The utility forcibly takes syncpoints as required and issues the warning message CSQU087I. If the function subsequently fails, the changes already committed are not backed out. Do not just rerun the job to correct the problem or you might get duplicate messages on your queues. Instead, use the current depth of the queue to work out, from the utility output, which messages have not been backed out. Then determine the most appropriate course of action. For example, if the function is LOAD, we can empty the queue and start again, or we can choose to accept duplicate messages on the queues.

To avoid such difficulties if the function fails, but at the risk of incurring a large CPU cost, set MAXUMSGS to be greater than:

• The number of messages in the queue, if you are working with a single queue.

• The number of messages in the longest queue in the page set, if you are working with an entire page set.

Use the DISPLAY QSTATUS command to find out the value of the CURDEPTH attribute, which is the current depth of the queue. To find out the value of MAXUMSGS, use the DISPLAY QMGR MAXUMSGS command. See the WebSphere MQ Script (MQSC) Command Reference manual for more information about these commands.