IBM SC34-7012-01 manual Examples of synchronization points, Units of work and syncpoints

–EXEC CICS CREATE CONNECTION COMPLETE

–EXEC CICS DISCARD CONNECTION

–EXEC CICS DISCARD TERMINAL

A UOW that does not change a recoverable resource has no meaningful effect for the CICS recovery mechanisms. Nonrecoverable resources are never backed out.

A unit of work can also be ended by backout, which causes a syncpoint in one of the following ways:

vImplicitly when a transaction terminates abnormally, and CICS performs dynamic transaction backout

vExplicitly by EXEC CICS SYNCPOINT ROLLBACK commands issued by an application program to backout changes made by the UOW.

Examples of synchronization points

In Figure 1, task A is a nonconversational (or pseudoconversational) task with one UOW, and task B is a multiple UOW task (typically a conversational task in which each UOW accepts new data from the user). The figure shows how UOWs end at syncpoints. During the task, the application program can issue syncpoints explicitly, and, at the end, CICS issues a syncpoint.

Unit of work

Task A

SOT

EOT

(SP)

UOW

UOW

UOW

UOW

Task B

SOT

EOT

SP

SP

SP

Abbreviations:

(SP)

EOT:

End of task

SOT:

Start of task

UOW:

Unit of work

SP:

Syncpoint

Figure 1. Units of work and syncpoints

Figure 2 on page 17 shows that database changes made by a task are not committed until a syncpoint is executed. If task processing is interrupted because of a failure of any kind, changes made within the abending UOW are automatically backed out.

If there is a system failure at time X:

vThe change(s) made in task A have been committed and are therefore not backed out.

vIn task B, the changes shown as Mod 1 and Mod 2 have been committed, but the change shown as Mod 3 is not committed and is backed out.

vAll the changes made in task C are backed out.

16CICS TS for z/OS 4.1: Recovery and Restart Guide