CICS® VR undo logging

CICS® VR undo logging writes a before-image log record to a log stream for every update made to a VSAM data set by a batch job. If the batch job encounters an abend, CICS® VR batch backout processing can use these records to remove the updates made by the failed batch job or batch job step.

Like CICS® VR forward recovery logging, CICS® VR undo logging can use different log streams, which are known as undo logs. However, an undo log cannot be assigned to a specific VSAM sphere. You can use the Undo logs assignment feature of CICS® VR to associate an undo log with:
  • A user ID
  • A job name prefix
  • The high-level qualifier of a VSAM sphere name
When you submit a VSAM sphere update job which involves undo logging, CICS® VR searches for any matching associations that you have set up between these elements of the job and a particular undo log. When CICS® VR finds an association that applies for a submitted job, it writes undo records to the undo log named for the association. The CICS® VR User's Guide explains how to create undo log associations using the CICS® VR ISPF dialog interface as part of the information on customizing CICS® VR undo logs.

The undo logs must be used only by CICS® VR undo logging. No other applications, such as forward recovery logging, writes to these log streams.

Only one undo log can be used for each VSAM sphere update job. For example, if a job updates more than one VSAM sphere, you cannot associate some of the VSAM spheres with a different undo log; they must all be associated with the same undo log. Because there are different types of undo log association, some jobs which you submit might have more than one matching association. When you submit a job, CICS® VR checks that there are no conflicting associations which name different undo logs. If a conflict is found, CICS® VR undo logging produces an error.

If CICS® VR does not find any associations which apply for a submitted job, it uses the default undo log which is defined for the system. You need to define the default undo log, by setting the default undo log name prefix, before you submit any job involving undo logging. You also need to specify an undo logging control string and a backout control string.