What is CICS® VR VSAM batch logging?

CICS® VR VSAM batch logging provides logging for your batch changes to VSAM data sets that are not accessed in RLS-mode.

This means that your CICS® transactions and your batch jobs that use CICS® VR VSAM batch logging cannot update the same VSAM data set at the same time. Once you have disabled the file from CICS®, you can use CICS® VR VSAM batch logging to log your application's batch updates. The following types of VSAM batch logging are available:
  • Forward recovery logging (REDO logging)
  • Undo logging
  • Replication logging

CICS® VR forward recovery logging records an after-image log record for every update made to the VSAM data set by a batch job. Therefore allowing you to run CICS® VR forward recovery to recover the batch updates if the data set becomes corrupted.

CICSVR undo logging records a copy of the data prior to any changes being made, so UNDO logging is always done when any indication is given of intent to update the data, therefore allowing you to run CICSVR batch backout to remove the batch updates if the batch job encounter an abend.

UNDO logging is done for the following VSAM commands in the application:
GET UPD
Get a record with the intent to update or erase it.
PUT ADD
Add a new record.
UNDO records are not written to the undo log for a PUT UPD or ERASE request because these operations modify existing records that are first obtained using GET UPD.

If a batch job reads all records using GET UPD commands even though only a few records are actually updated, CICSVR undo logger records every before-image record. However, unless a record is updated, logging the before image is not necessary and it adds to the overhead and runtime of the batch job. Also batch backout takes longer when before-images are written back to a data set but they only replace identical records. The alternate approach to avoid such overhead is to specify FRLOG(ALL) for the sphere. In this case, if a subsequent PUT_UPDATE or ERASE is not done, CICS VR will remove the GET for UPDATE UNDO record if it is still present in the log buffer

CICS VR replication logging records both the before-image and the after-image log records in the replication log. If both forward recovery and replication logging are requested for the VSAM sphere, the VSAM batch logger shares the forward recovery log for forward recovery logging and replication logging. If both undo and replication logging are requested for the VSAM sphere, VSAM batch logger uses separate logs for undo logging and replication logging.