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UERCNORM
Do not perform the backout of this log record. Any updates
performed by the batch run should take precedence.
UERCBCKO
Perform the backout. It is known that the actions of the batch job
could not have affected this update.
A return code of UERCPURG is not allowed. There is no need to set a
UERCPURG return code, because this global user exit is invoked during
syncpoint phase 2, and therefore cannot get a purged response from any
calls that it makes.
XPI calls
All can be used, but subject to the same caution as for API and SPI calls.
API and SPI calls
Although this exit is allowed to issue API and SPI calls, you should be very
careful about which commands you use because the exit is invoked during
file backout, which is part of syncpoint phase 2.
It is recommended that you restrict EXEC CICS commands to inquiries, and
avoid commands that update CICS resources, because the resources may
themselves be in a state of recovery. In particular, the following restrictions
apply:
1. Do not issue any recoverable operations.
2. Do not use operations that access systems or resource owners external
to this CICS, even if the target resource is non-recoverable.
3. Do not disable or close files, because this could cause further error
conditions.
4. It is possible for this exit to be invoked under a different transaction
environment from that under which the updates that are being backed
out were originally made. If your exit program wants to perform any
actions (such as writing a message to the terminal) that require it to be
running under the original transaction environment, it must first check
the value returned in the RE_ATTACHED_TRANSACTION parameter of
a transaction manager INQUIRE_TRANSACTION XPI call.
DFH$FCBV sample global user exit program: DFH$FCBV provides sample
processing for the file control backout override global user exit, XFCBOVER. The
exit program, if enabled at the XFCBOVER exit point, is invoked when a log record
is presented to file control for backing out an update to a data set in RLS access
mode, after the data set has been used in a batch update despite the existence of
retained locks. A consequence of running a batch program while there are retained
locks is that a lock that protected a record updated by CICS could have been
overridden by a non-RLS batch program.
There is more information about using the XFCBOVER exit, and about the
DFH$FCBV sample program, in the comments within the DFH$FCBV source code.
The comments also include some suggested extensions that you can make to the
sample program to reflect the pattern of batch usage at your installation.
In summary, DFH$FCBV performs the following processing:
v Makes a user trace entry if tracing is active for file control. This has trace point id
X'01E0' and traces:
– An eye-catcher ‘DFH$FCBV ENTRY’
134 Customization Guide