Setting the CICS® VR undo logging control string

The CICSVR_UNDOLOG_CONTROL parameter in the active IGDSMSxx member of SYS1.PARMLIB is used to enable or disable CICS® VR undo logging on the system, specify the action that CICS® VR must take if an undo logging failure occurs, and specify if CICS® VR must perform synchronous undo logging.

The following values can be specified for the CICSVR_UNDOLOG_CONTROL parameter in the active IGDSMSxx member:
ENABLE CONT
Enable CICS® VR undo logging and allow a client application, batch job, to continue execution when an error occurs with the undo log stream. VSAM sphere updates are not synchronized with CICS® VR undo logging. ENABLE CONT is the default value for the CICS® VR undo logging control string.
ENABLE TERM
Enable CICS® VR undo logging and cancel a client application, batch job, in the case that an error is encountered with the undo log stream. VSAM sphere updates are not synchronized with CICS® VR undo logging.
ENABLE SYNC
Enable CICS® VR undo logging and cancel a client application, batch job, in the case that an error is encountered with the undo log stream. VSAM sphere updates are synchronized with CICS® VR undo logging.
DISABLE
Disable CICS® VR undo logging on the system.
Note:
If an undo logging error occurs, but the log stream is still accessible, for example; the log structure becomes full, you might want to immediately cancel the batch job, and remove all updates made by the step that was in progress when the logging error occurred. However, you can perform a successful batch backout only when ENABLE SYNC has been specified. SYNC verifies that every log record is successfully written to the undo log stream before control returns to VSAM.

If SYNC was not specified, and a undo logging error occurs, then it might be possible that one or more updates have been made to VSAM data sets that are not reflected in the undo log stream. In this scenario, you would need to restore the affected VSAM spheres from a backup and either run forward recovery or rerun the relevant transactions.

Specifying SYNC could greatly increase the overhead processing of the batch jobs, and might not be ideal in all environments.

Examples
CICSVR_UNDOLOG_CONTROL(ENABLE CONT)
Enable CICS® VR undo logging for all VSAM spheres defined with FRLOG ALL or UNDO and allow a client application, batch job, to continue when a logging error occurs. The VSAM sphere updates are not synchronized with CICS® VR undo logging.
CICSVR_UNDOLOG_CONTROL(DISABLE)
Disable CICS® VR undo logging. No undo logging is performed regardless of the FRLOG settings for the VSAM spheres.