Dynamic transaction backout:
Dynamic transaction backout backs out the effects of a transaction that has terminated abnormally. CICS restores the recoverable resources to the consistent state in which they were at the beginning of the interrupted LUW (that is, at the most recent syncpoint or start of task).
Dynamic transaction backout is similar in effect to the backout of in-flight tasks during automatic restart following a CICS error. The most important differences are that dynamic transaction backout operates on a single abnormally terminating transaction and that CICS performs the backout while the remainder of the CICS system continues to run normally. Dynamic transaction backout thus provides immediate recovery of data integrity following the abnormal termination of a transaction.
Through dynamic transaction backout, CICS cooperates with one or more file managers to back out changes that are made by the abnormally terminating transaction.
Causes of a transaction error include the following: A software exception or signal that is raised in the application program, for which CICS abnormally terminates the offending task An invalid request to CICS from an application, which causes an abnormal termination A task that issues an EXEC CICS ABEND request.
If the transaction is in error, CICS saves information about its initial state and backs out the changes that were made by the interrupted LUW so that recoverable resources do not remain in a partially updated or inconsistent state.
The backout of an individual transaction is called dynamic transaction backout.
Dynamic transaction backout is a way of undoing changes that have been made to recoverable resources. When an LUW backs out, CICS cooperates with other recoverable servers that have been involved in the LUW, to undo the effects of any changes that have been made to recoverable resources.
Suppose that an LUW updates a temporary storage queue record, writes a transient data queue record, then backs out. CICS maintains some state information about the queues that it backs out, then requests the file manager to undo the changes.
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