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The recovery manager also drives:
v The backout processing for any units of work that were in a backout-failed state
at the time of the CICS failure
v The commit processing for any units of work that had not finished commit
processing at the time of failure (for example, for resource definitions that were
being installed when CICS failed)
v The commit processing for any units of work that were in a commit-failed state
at the time of the CICS failure
See “Unit of work recovery” on page 73 for an explanation of the terms
commit-failed and backout-failed.
The recovery manager drives these backout and commit processes because the
condition that caused them to fail might be resolved by the time CICS restarts. If
the condition that caused a failure has not been resolved, the unit of work remains
in backout- or commit-failed state. See “Backout-failed recovery” on page 79 and
“Commit-failed recovery” on page 83 for more information.
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 units of work 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:
v The VSAM ICF catalog entry for the data set if it is defined there, and if
RLS=YES is specified as a system initialization parameter. In this case, CICS
file control manages writes to the log stream directly.
v A journal model definition referenced by a forward recovery journal name
specified in the file resource definition.
Chapter 1. Recovery and restart facilities 7