You must define a system log if you want to preserve data integrity
in the event of unit of work failures and CICS® failures.
A system log is mandatory for the following situations:
- The backout of recoverable resources changed by failed units of work.
- Cold starts, to enable CICS to restore units of work that were shunted at the
time of the shutdown.
- Warm restarts, to enable CICS to restore the region to its state at the previous
shutdown, including units of work that were shunted at the time of the shutdown.
- Emergency restarts, to enable CICS to perform the following tasks:
- Restore the region to its state at the previous shutdown, including units
of work that were shunted at the time of the shutdown.
- Recover units of work that were in-flight at the time of the CICS failure
and perform backout of recoverable resources that were updated before the
failure.
CICS log
manager connects to its log stream automatically during system initialization,
unless it is defined as TYPE(DUMMY) in a CICS JOURNALMODEL resource definition.