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Exit XFCBOVER, file control backout override exit
XFCBOVER is part of the support CICS file control provides for “batch windows” in
a VSAM RLS environment.
VSAM RLS locks individual records within a data set, and these locks are converted
to retained locks for those UOWs that are not completed because of backout or
in-doubt failures, thus preserving data integrity. To avoid corruption of a data set by
a non-RLS batch job, which is not aware of the retained record locks, a data set
cannot normally be opened for update in non-RLS mode if it has any locked
records.
Retained lock override for batch
There may be circumstances in which you want to override these locks and force
the open of a data set for batch processing. For example, when:
v There is insufficient time available, before running the batch job, in which to
resolve the situation that caused the records to be locked, or
v It is known that the batch job cannot harm data integrity (because it does not
update existing records in the data set, or it does not update any records that
CICS may have updated).
To override the open restriction, VSAM RLS provides the SHCDS
PERMITNONRLSUPDATE command, to allow a non-RLS batch job to open a
sphere for update even when there are retained locks.
Effect of retained lock override on CICS
VSAM records the use of the option to override retained locks, so that it can notify
a CICS region when the region next opens the data set. Because data could have
been altered by the non-RLS batch job, the results of CICS performing any
recovery (on UOWs that were in a backout-failed or indoubt-failed state at the time
of the batch job) are unpredictable. In this situation, therefore, the default CICS
action is not to back out any updates that were outstanding at the time that locks
were overridden, and to write diagnostic information about each backout ignored to
the CSFL transient data queue.
The XFCBOVER global user exit is provided to enable you, for each UOW log
record for which backout is being ignored, to:
v Write application-related diagnostics to supplement those provided by CICS
v To perform application-related recovery actions
v To reverse the default by requesting that the backout should be carried out after
all. This option is required for the case where the batch job is known not to
corrupt data integrity (for example, because it only inserts records).
file control recovery program exits
Chapter 1. Global user exit programs 119