Resynchronizing the session

When a session is active, both IMS and CICS® maintain a set of SNA message sequence numbers for that session. When a failure occurs and restart is attempted, the total of sync points on the session is checked between the subsystems by the STSN command.

The CICS/IMS session resumes if both of the following are true:

The session is being cold-started.
The half sessions' sequence numbers agree, or are within acceptable limits.

If a session fails, a CICS transaction having pending activity for that session also fails. CICS uses dynamic transaction backout (DTB) to ensure integrity of recoverable resources. The DTB indoubt parameter must be specified as IN-DOUBT(WAIT) or DTB=(YES,WAIT) in order to ensure consistency between the IMS and CICS subsystems within an ISC network.

WAIT holds locks on recoverable resources until resynchronization occurs.

If this situation is undesirable, you can specify IN-DOUBT(BACKOUT) or DTB=YES on an IMS-CICS ISC transaction. However, doing so might cause duplicate messages to be sent to IMS after session resynchronization, and can require logic in the IMS user transaction to resolve them.

If the DTB indoubt parameter does not specify WAIT, you must specify FORCSESS on the IMS TERMINAL macro system definition OPTIONS parameter or use an authorized IMS terminal operator /CHANGE command.