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:
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.
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:
Forward recovery journal names are of the form DFHJnn where nn is a number in the range 1-99 and is obtained from the forward recovery log id (FWDRECOVLOG) in the FILE resource definition.
In this case, CICS creates a journal entry for the forward recovery log, which can be mapped by a JOURNALMODEL resource definition. Although this method enables user application programs to reference the log, and write user journal records to it, you are recommended not to do so--you should ensure that forward recovery log streams are reserved for forward recovery data only.
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.
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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