Message ordering

For a particular topic, messages are published by the queue manager in the same order as they are received from publishing applications (subject to reordering based on message priority).

Message ordering normally means that each subscriber receives messages from a particular queue manager, on a particular topic, from a particular publisher in the order that they are published by that publisher.

However, as with all IBM® MQ messages, it is possible for messages, occasionally, to be delivered out of order. This can happen in the following situations:
  • If a link in the network goes down and subsequent messages are rerouted along another link
  • If a queue becomes temporarily full, or put-inhibited, so that a message is put to a dead-letter queue and therefore delayed, while subsequent messages pass straight through.
  • If the administrator deletes a queue manager when publishers and subscribers are still operating, causing queued messages to be put to the dead-letter queue and subscriptions to be interrupted.
If these circumstances cannot occur, publications are always delivered in order.
Note: It is not possible to use grouped or segmented messages with Publish/Subscribe.