Syncpoints in IMS applications

In an IMS application, you establish a syncpoint by using IMS calls such as GU (get unique) to the IOPCB and CHKP (checkpoint).

To back out all changes since the previous checkpoint, you can use the IMS ROLB (rollback) call. For more information, see the following:

IMS/ESA® Application Programming: Transaction Manager
IMS/ESA Application Programming: Design Guide

The queue manager is a participant in a two-phase commit protocol; the IMS syncpoint manager is the coordinator.

All open handles are closed by the IMS adapter at a syncpoint (except in a batch or non-message driven BMP environment). This is because a different user could initiate the next unit of work and IBM® MQ security checking is performed when the MQCONN, MQCONNX, and MQOPEN calls are made, not when the MQPUT or MQGET calls are made.

However, in a Wait-for-Input (WFI) or pseudo Wait-for-Input (PWFI) environment IMS does not notify IBM MQ to close the handles until either the next message arrives or a QC status code is returned to the application. If the application is waiting in the IMS region and any of these handles belong to triggered queues, triggering will not occur because the queues are open. For this reason, applications running in a WFI or PWFI environment should explicitly MQCLOSE the queue handles before doing the GU to the IOPCB for the next message.

If an IMS application (either a BMP or an MPP) issues the MQDISC call, open queues are closed but no implicit syncpoint is taken. If the application ends normally, any open queues are closed and an implicit commit occurs. If the application ends abnormally, any open queues are closed and an implicit backout occurs.