Using structure full monitoring with CQS structure overflow

You can use the structure full monitoring function (a z/OS® function) with the structure overflow function (a CQS function) for queue structures.

The overflow threshold is a value defined to CQS. The structure full threshold is a value defined to z/OS. If the overflow threshold is close to the structure full threshold and automatic altering is enabled, CQS and z/OS might both try to initiate a structure alter at the same time to prevent the structure from becoming full.

If a CQS-initiated structure alter is in progress when z/OS detects the structure full threshold has been reached, z/OS stops the CQS-initiated structure alter and initiates its own structure alter. When CQS detects that its structure alter has failed, CQS goes into overflow mode, even if the z/OS-initiated structure alter reduces the structure usage below the overflow threshold.

Recommendation: Consider your structure full threshold when deciding what overflow threshold to define, so that you control when a structure goes into overflow mode. If you use structure full threshold, define it to be lower than the overflow threshold to avoid going into overflow mode unnecessarily. If the structure full threshold is lower than the overflow threshold, z/OS can attempt structure full threshold processing before the structure goes into overflow mode.

Related reading:

For detailed information about the CQSSGxxx member of the PROCLIB data set, see IMS Version 15.5 System Definition.
For detailed information about the Queue Overflow User-Supplied exit routine, see IMS Version 15.5 Exit Routines.
For detailed information about the CQSPUT request, see IMS Version 15.5 System Programming APIs.