CQS structure recovery

The structure recovery function recovers the data objects on a structure from the SRDS and the z/OS® logs after a structure failure.

After a structure failure, the structure might need to be recovered if it is empty or contains only CQS control information. During structure recovery, CQS allocates a structure and repopulates it from either the SRDS (containing valid client data from a previous checkpoint) and the CQS log or the CQS log by itself.

When CQS recovers the structure from a structure checkpoint, it repopulates the structure with the data objects from the structure recovery data set. CQS reads the log starting at the time of the structure checkpoint to update the structure with changes that occurred after the structure checkpoint.

If the primary structure is empty and neither SRDS contains valid structure checkpoint data, CQS determines whether it can use just the CQS log for recovery. If the first log record in the log stream is the Beginning of Log log record, the log stream contains all of the log records required for recovery and CQS can use the log record to complete the structure recovery.

If CQS finds that a previous structure rebuild did not complete successfully, it initiates another rebuild.

If the primary structure contains only CQS control information and the CQS that allocated the structure is not able to determine if a rebuild is necessary, CQS initiates a rebuild if either SRDS is valid or all log records are available.

If neither SRDS is valid and the log records are deleted by a previous structure checkpoint, CQS cannot rebuild the structure. In this case, if rebuild is necessary, CQS issues WTOR CQS0034A to ask you what to do. You can cold start the structure or cancel this CQS.

If no CQS has access to the structure when structure rebuild is initiated, the structure is recovered from the SRDS and the CQS log. Nonrecoverable data objects (such as IMS Fast Path input messages) are lost. Data objects are read from the SRDS and copied into a new structure. CQS then reads the log to bring the structure back to the point of currency. The log contains all the records necessary for structure recovery if no structure checkpoint was ever initiated. In this case, the structure is recovered from just the CQS log.

A client can use the CQSCONN request to specify whether work can be performed while a structure is being rebuilt. While structure recovery is in progress, CQS stops all activity against the structure. This means that CQS requests are held until the structure recovery is complete. You can allow CQS requests to continue during structure rebuild by specifying WAITRBLD=NO when connecting to the structure with the CQSCONN request. In this case, structure recovery stops structure activity for some time, but the structure becomes available much sooner.