Message queue data set failures

Two types of problems can occur with message queue data sets: they can run out of space, or an I/O error can occur. In either case, you need to scratch and reallocate the problem data set, and increase its size if necessary.

Note: This topic does not apply to a DBCTL environment or to a shared-queues environment.

IMS automatically reconstructs the contents of the message queues when you restart IMS and specify the BUILDQ and FORMAT keywords on the restart command.

Restriction: IMS can only reconstruct the message queue data sets from the initial cold start or from a SNAPQ or DUMPQ checkpoint.

To recover message queues during IMS restart, use the /NRE BUILDQ or /ERE BUILDQ command. If you also want to reinitialize the message queue data sets (that is, reformat them with null records), use the FORMAT keyword on the restart command.

To use the /NRE BUILDQ command, you must have previously shut down IMS using a /CHECKPOINT DUMPQ | PURGE command. You can use the/ERE BUILDQ command to recover messages from a prior SNAPQ checkpoint (/CHECKPOINT SNAPQ).

If an emergency restart fails, you must initiate an emergency cold start using the /ERE COLDSYS command. An emergency cold start does not perform any database recovery, so you must close and archive the last OLDS.

If an IMS restart fails, you can use the IBM® IMS Queue Control Facility for z/OS® (QCF) to recover the message queues if you use one of the following cold start commands after the failed restart: /ERE CHECKPOINT 0, /ERE COLDCOMM, or /ERE COLDSYS. With QCF, you can select messages from the OLDS or an SLDS and requeue them to the message queues after IMS restarts (cold start). QCF provides recovery modes that analyze and select the messages to be requeued.