You can use the DEBUG facility to trap unauthorized alterations of checkpoint-resident data, a job queue element (JQE), or a job output element (JOE) by specifying the $T DEBUG=Y|N command. It can also be used (if additional parameters are included with the command) to record certain JES2 events and activities. For example, you can specify whether to count certain events, provide certain $HASP095 error information to the operator, verify the integrity of a newly created checkpoint version, or, start or stop monitoring updates made to the checkpoint data set.

Because the DEBUG facility checks all checkpoint records before processing them, DEBUG causes performance degradation. Use the $T DEBUG=Y|N command only when you experience problems that you suspect are checkpoint I/O problems. Also, because of performance degradation, IBM® suggests that you do not use the DEBUG command with the CKPT or VERSION parameters specified in a production environment.