CICS forward recovery

Some types of data set failure cannot be corrected by backward recovery; for example, failures that cause physical damage to a database or data set. Recovery from failures of this type is usually based on the following actions:

  1. Take a backup copy of the data set at regular intervals.
  2. Record an after-image of every change to the data set on the forward recovery log (a general log stream managed by the MVS™ system logger).
  3. After the failure, restore the most recent backup copy of the failed data set, and use the information recorded on the forward recovery log to update the data set with all the changes that have occurred since the backup copy was taken.

These operations are known as forward recovery.

On completion of the forward recovery, as a fourth step, CICS® also performs backout of UOWs that failed in-flight as a result of the data set failure.

Forward recovery of CICS data sets

CICS supports forward recovery of VSAM data sets updated by CICS file control (that is, by files or CICS-maintained data tables defined by a CICS file definition).

CICS writes the after-images of changes made to a data set to a forward recovery log, which is a general log stream managed by the MVS system logger.

CICS obtains the log stream name of a VSAM forward recovery log in one of two ways:

  1. For files opened in VSAM record level sharing (RLS) mode, the explicit log stream name is obtained directly from the VSAM ICF catalog entry for the data set.
  2. For files in non-RLS mode, the log stream name is derived from:
Note:
You cannot use a CICS system log stream as a forward recovery log.

The VSAM recovery options or the CICS file control recovery options that you require to implement forward recovery are explained further in Defining files as recoverable resources.

For details of procedures for performing forward recovery, see Forward recovery procedures.

Forward recovery of other (non-VSAM) resources

CICS does not provide forward recovery logging for other resources, such as BDAM files. However, you can provide this support yourself by ensuring that the necessary information is logged to a suitable log stream. In the case of BDAM files, you can use the CICS autojournaling facility to write the necessary after-images to a log stream.

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