Data integrity

XCICS ensures data integrity on file through the XVSAM logging features.

All operations on files are tracked on the recovery log file. Every XCICS instance has its own recovery log containing all information concerning both committed and "in-flight" transactions.

The recovery log is used to perform:

The recovery log is by default named RECOVERY.LOG and using the configuration directive recovery_log_path, it is possible to define the path where XCICS will create the file. For safety reasons, it's better to keep this file not on the same disk where XVSAM data are stored.

XCICS Warm start

Normally, when XCICS is cold started (xcicsctl start), it generates a new recovery log. In case of abnormal XCICS termination (i.e. hardware fault with cluster switch-over), it is possible to restart XCICS in "warm" mode (xcicsctl warmstar).

When XCICS is warm-started, it reads the existing recovery log, and backs-out all the "in-flight" transactions of the previous instance.  In other words it removes all uncommitted transaction from XVSAM files.

Additionaly, it preserves also existing Transient Data records, to continue eventual uncompleted background processing.

Warm start processing on XVSAM data is also possible by command line using the xvsam utility (--warm-start option).

After-Image processing

On some situations, i.e. serious hardware faults, it is necessary to rebuild the XVSAM information starting from a backup.

With the after-image processing, it is possible to restore an existing backup and use the XCICS recovery log to apply all changes occurred on files tracked in the log.

In this case, user have to:

Of course, backup data and recovery log must be congruent.