Synchronization

Synchronization makes a group of updates succeed or fail together as one unit of work.

EXEC CICS SYNCPOINT commits the unit of work; SYNCPOINT ROLLBACK undoes it.

What is a unit of work

• A unit of work is the set of recoverable changes made since the last syncpoint, or since the task started.
• Recoverable resources include VSAM files, DB2 tables, temporary storage queues, and transient data.
• At syncpoint CICS uses two-phase commit so that all resources agree on commit or backout together.
• If the task abends, CICS automatically backs out the incomplete unit of work.

SYNCPOINT

• EXEC CICS SYNCPOINT ends the current unit of work and starts a new one.
• All updates since the last syncpoint are committed and made permanent.
• Locks and enqueues held by the task are released at syncpoint.
• Issue syncpoints at business boundaries, for example after one complete order is processed.

ROLLBACK

• EXEC CICS SYNCPOINT ROLLBACK backs out every change in the current unit of work.
• Use it when validation fails after updates were already made.
• After rollback the program can display an error and continue, or end the task.
• Never issue updates you cannot afford to lose before you decide whether to roll back.

Example of SYNCPOINT and ROLLBACK

• Commit when the order is complete; back out when validation fails.
• *--- commit the completed order --- EXEC CICS SYNCPOINT END-EXEC. *--- back out when validation fails --- IF WS-VALIDATE-FAILED EXEC CICS SYNCPOINT ROLLBACK END-EXEC END-IF.
• After the rollback the file looks exactly as it did at the previous syncpoint.