CICS group attach

CICS® group attach provides the ability for a CICS region to connect to any active member of an IBM MQ queue sharing group on the same LPAR rather than specifying an individual queue manager. CICS still connects to a single queue manager at a time.

You require at least two queue managers on the LPAR to support CICS group attach. Using group attach provides higher availability as we do not need a particular queue manager to be active. CICS connects to any queue manager in the queue sharing group on the LPAR.

For more information, see the CICS documentation on the MQCONN resource.

CICS attempts to connect to MQNAME passed as if it were a queue manager:

• If the queue manager exists and is active, the connection will work.
• If the connection fails, CICS queries the status of queue managers in the group to ascertain which are active on same LPAR.
• If multiple queue managers are active, CICS checks for RESYNCMEMBER(YES) and the UOW status to determine whether CICS needs to connect, or should connect, to a particular member, or wait if not active.
• If there is no need to connect to a particular member, CICS selects a queue manager (using a randomizing algorithm).
• CICS attempts to connect to chosen queue manager.
• If the attempt fails then, depending upon the return code, CICS chooses the next member, then goes through the selection loop again.
• If no queue managers are active, CICS issues multiple connections to the list of queue managers and waits on ECBLIST until the first queue manager becomes available.