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Message ordering

For a given stream, messages are published by brokers in the same order as they are received from publishers (subject to reordering based on message priority). This normally means that each subscriber receives messages from a particular broker, on a particular topic and stream, from a particular publisher in the order that they are published by that publisher.

However, as with all WebSphere 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 broker or uses the clrmqbrk command (CLRMQMBRK on iSeries) 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.

 

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