Undelivered/unprocessed messages

This topic describes what happens to undelivered and unprocessed messages on the SYSTEM.QSG.TRANSMIT.QUEUE.

If an IGQ agent cannot deliver a message to the destination queue, the IGQ agent:

• Honors the MQRO_DISCARD_MSG report option (if the Report options field of the MQMD for the undelivered message indicates that it must) and discards the undelivered message.
• Attempts to place the undelivered message on to the dead letter queue for the destination queue manager, if the message has not already been discarded. The IGQ agent prefixes the message with a dead letter queue header (MQDLH).

If a dead letter queue is not defined, or if an undelivered message cannot be put to the dead letter queue, and if the undelivered message is:

• persistent, the IGQ agent backs out the current batch of persistent messages that it is processing, and enters a state of retry. For more information, see Specific properties of intra-group queuing.
• non-persistent, the IGQ agent discards the message and continues to process the next message.

If a queue manager in a queue sharing group is terminated before its associated IGQ agent has had time to process all its messages, the unprocessed messages remain on the SYSTEM.QSG.TRANSMIT.QUEUE until the queue manager is next started. The IGQ agent then retrieves and delivers the messages to the destination queues.

If the coupling facility fails before all the messages on the SYSTEM.QSG.TRANSMIT.QUEUE have been processed, any unprocessed non-persistent messages are lost.

IBM® recommends that applications do not put messages directly to transmission queues. If an application does put messages directly to the SYSTEM.QSG.TRANSMIT.QUEUE, the IGQ agent might not be able to process these messages and they remain on the SYSTEM.QSG.TRANSMIT.QUEUE. Users then have to use their own methods to deal with these unprocessed messages.