Monitoring shared message queue usage with the Queue Space Notification exit routine (DFSQSSP0)

IMS provides the Queue Space Notification exit routine for shared queues (DFSQSSP0) with feedback on the overall utilization of the shared message queue structures on the coupling facility so that a solution can be implemented in the exit to monitor and prevent queue structures from becoming full.

When IMS runs by using shared queues, it stores transaction messages on the IMS shared messages queues coupling facility structure. The structure usage fluctuates during business operation depending on how busy the system is and how fast the transaction processing rate is. The structure might overflow if the rate of the messages arriving is faster than the rate of the messages being processed. The full condition of the shared queues might affect system availability.

You can receive information, through the Queue Space Notification exit routine, about how much of the message queue structure is used for both the primary structure and overflow structure:

This structure usage information is updated whenever IMS puts a message to the shared queue structure or deletes a message from the shared queue structure. The DFSQSSP0 exit parameter list, DFSPARM, provides input and output parameters for communication between IMS and the user exit DFSQSSP0.

In the Queue Space Notification exit parameter list DFSPARM, under the existing PARM DSECT, the following fields can be used to receive structure usage information:
  • QSPCFBKP - Structure feedback area address
  • QSPCFBKL - Structure feedback area length

For details about the feedback area, see the CQSSFBA macro, which is shipped with IMS.

Warning: The Queue Space Notification exit for shared queues (DFSQSSP0) provides structure utilization information only about the IMS shared message queue structure. It does not provide information about the IMS shared EMH structure.