• The IMS program isolation function ensures database integrity. All database modifications and message creation by an application program is isolated from any other application programs running in the IMS system until an application program completes a synchronization point. This ensures that only committed data can be used by concurrent application programs. A synchronization point is established with a message Get Unique (GU) call for a new input message, a checkpoint call, or application program normal termination.
• Program isolation allows two or more application programs to concurrently run with common data segment types, even when the processing intent is to update, add, or delete.
• With program isolation and dynamic back out, it is POSSIBLE to resolve potential database deadlock situations transparent to the application programs.

The following sequence of events is an example of a deadlock:

• Program A updates database ELEMENT X.
• Program B updates database element Y.
• Program A requests Y and must WAIT for the synchronization point of program B.
• Program B in turn requests X and must wait for the synchronization point of program A.

The following sequence of events is an example of a deadlock: