Understanding nonrecoverable versus recoverable resources

With VSAM file recovery, there are two different types of resources, ones that are not recoverable and ones that are recoverable.

Nonrecoverable Data Sets: Nonrecoverable data sets are those for which updates are committed immediately, and therefore cannot be backed out. These data sets can be read and updated by both CICS® and batch jobs but neither CICS nor VSAM provides any support for forward recovery logging for a nonrecoverable data set.

Recoverable Data Sets: A recoverable data set is one that participates in syncpoint activity and is eligible for changes to be backed out in the event of a transaction failure. When several changes are made to a recoverable data set from within a unit-of-work (UOW), these changes are either all committed, or all backed out, together.

The ICF catalog recovery option allows you to specify the following requirements:
  • No recovery is required; the sphere is not recoverable.
  • Backout is required; the sphere is recoverable.
  • Backout and forward recovery are required; the sphere is recoverable.
If you also require a forward recovery capability for recoverable data sets, you must specify in the ICF catalog the name of the MVS log stream that CICS uses as the forward recovery log. This log stream name must match the name of a log stream that is defined to the MVS system logger.

If you specify forward recovery for a data set (LOG=ALL) VSAM might not check that you have specified the required forward recovery MVS log stream name. However, CICS performs this check when it opens a file against a data set that has an ICF catalog entry that specifies forward recovery. CICS fails the open request if the ICF catalog forward recovery attributes are inconsistent.

The section that follows focuses on recoverable data sets, that is, data sets that can be recovered using CICS VR. The following topics are described:
  • Backup-while-open (BWO)
  • VSAM RLS
  • CICS System Definition data