Message queue backup copies

Messages (the transaction requests entered by end users, and the responses going back to them) are stored on queues before being processed. If you are not sharing the IMS message queues, messages are stored in the message queue data set, which resides partly on disk and partly in virtual storage.

In a shared-queues environment, IMS messages are kept on a coupling facility. When IMS takes a regular system checkpoint, it does not record the contents of the message queues, just as it does not record the contents of the databases.

When you shut down IMS normally (rather than abnormally), any changed messages in virtual storage (not on a coupling facility) are automatically written to the disk portion of the message queue data set. Therefore, if you periodically shut down IMS, there is little or no need to backup the message queues manually.

When you run IMS for extended periods without shutting it down, you might want to back up the message queues periodically. In a non-shared-queues environment, use the /CHECKPOINT SNAPQ command to back up the message queues; this command does not shut down IMS.

In a shared-queues environment, you must periodically back up the shared queues. Use the /CQCHKPT command to copy IMS messages to the Common Queue Server's structure recovery data set.

Backing up the message queues reduces the time required for recovery if problems arise with the message queue data sets.