CQS structure functions
CQS provides functions for monitoring structure status and capacity, and enabling structure recovery. Some of these functions are built-in functions and do not require intervention. Other functions are optional, and can be set up or initiated as your installation needs them.
Structure overflow
CQS provides a structure overflow function that automatically warns you when a queue structure is approaching full and takes action to prevent a full structure. When the usage of a structure reaches the overflow threshold, CQS attempts to make the structure larger by initiating a structure alter. If the alter fails, CQS either allocates an overflow structure and moves selected queues to the overflow structure (if you define an overflow structure), or prevents new data objects from being put on the selected queues.
The CQS client requests, CQSPUT and CQSDEL, can provide information about current structure utilization through the FEEDBACK= and FEEDBACKLEN= parameters. IMS uses this capability to provide structure utilization information about the IMS shared message queue structure to the Queue Space Notification exit routine for shared queues (DFSQSSP0). The structure utilization information contains the total number of allocated and in-use entries and elements in the primary and overflow structures. This information helps you prevent the message queue structure from becoming full. Note that DFSQSSP0 provides only information about the IMS shared message queue structure, not the IMS shared EMH structure.
Structure rebuild
Structure rebuild is a z/OS® process that allows another instance of a structure to be allocated with the same name and contain data reconstructed from the initial structure instance. z/OS supports system-managed rebuild, in which case z/OS rebuilds the structure. z/OS also supports user-managed rebuild; the user rebuilds the structure. Structure rebuild can be initiated manually by using an operator command, or automatically by CQS or z/OS.
CQS allows system-managed rebuild for queue structures and resource structures. CQS provides user-managed rebuild to support a structure copy function and a structure recovery function.
Structure copy copies the contents of a structure to another structure for planned reconfiguration. Structure copy is supported for resource structures and queue structures.
Structure recovery recovers a structure from the structure checkpoint data set and the CQS log after a structure failure. Structure recovery is supported for queue structures.
Structure duplexing
CQS can use the duplexing capabilities of z/OS. Duplexing occurs when the operating system creates a duplex (backup) copy of a structure, then maintains the two structures during normal mainline operation. If a structure fails, or a connection to a structure is lost, the operating system switches to the unaffected structure instance.