Handling transaction abends

IMS transaction abend

When an IMS transaction terminates abnormally, all changes to IMS resources that were performed by this transaction are backed out by IMS. If the transaction is synchronous (CICS SEND/SYNCPOINT), IMS sends a negative response (exception DR2) to CICS. This causes the CICS transaction to also terminate abnormally. As a result of the negative response and subsequent CICS transaction abend, CICS backs out any changes made to recoverable resources after the previous CICS sync point. An error message is also sent to CICS; CICS routes this message to the master terminal destination CSMT. The exception occurs when MFS output formats do not exist in the format library or incur an I/O error. In this case, IMS has already sent a positive sync-point response and must indicate the MFS error to CICS by using an ATTACH SYSMSG.

If the transaction is asynchronous (CICS START or SEND LAST), IMS sends an error message to CICS; CICS routes this message to its master terminal destination. The error message is preceded by either a SYSMSG or an ERP header, depending upon the type of error that occurs. If the error occurs before IMS sends a sync-point response to input, an exception response and ERP are used; if after the sync-point response, ATTACH SYSMSG is used.

CICS transaction abend

If a transaction is initiated by a CICS subsystem acting as a front end for IMS, and that CICS transaction terminates abnormally before reaching sync point, any processing performed is handled in accordance with the specification on the DEFINE TRANSACTION IN-DOUBT parameter (or DFHPCT DTB= parameter).

If an asynchronous transaction is initiated by an IMS front end and the CICS transaction abends upon receipt of the transaction, IMS is not notified. This is because the receipt of the message causes the CICS mirror transaction to return an immediate DR2 to the asynchronous input and to schedule a transaction to process it. If this scheduled transaction fails, the ISC link to IMS is no longer active and no notification is possible. CICS does, however, notify the CICS destination CSMT of the transaction failure.

During synchronous processing, if CICS is the secondary half session, the ALLOCATE command has been successfully issued, and no message is available to be sent to IMS (due, for example, to DTB causing backout), CICS automatically deallocates the session by sending LUSTATUS BB/EB to IMS.

If the synchronous transaction terminates abnormally any time after it has sent a message to IMS using the SEND/SYNCPOINT command, and that message has been enqueued on an IMS input queue, IMS processes it. When IMS attempts to send an output message to CICS, that message receives a negative response from CICS. As a result, the message can remain on the IMS output queue until it can be re-sent or until it is dequeued by the IMS master terminal operator.