[rabbitmq-discuss] rabbitmq cluster failover for persistent queues

Mon Jul 27 01:03:10 BST 2009

Yes, thank you for clarifying that Matthias.

On Sun, Jul 26, 2009 at 4:38 PM, Matthias Radestock <matthias at lshift.net>wrote:

> Charles,
>
> charles woerner wrote:
>
>> So in the case of competing consumers taking messages from a rabbitmq
>> broker cluster it sounds like once-and-only-once delivery is somewhat
>> up to the application to implement by arranging for each message to
>> be delivered to redundant queues (ie. 2 separate queues with similar
>> bindings residing on different hosts), then coordinate among your
>> consumers to ensure once-and-only-once delivery using a database or
>> simply to make your workflow idempotent with respect to the duplicate
>> messages.
>>
>
> Exactly-once requires coordination between consumers, or idempotency,
> even when there is just a single queue. The consumer, broker or network
> may die during the transmission of the ack for a message, thus causing
> retransmission of the message (which the consumer has already seen and
> processed) at a later point.
>
> Once that issue has been addressed in a system, the introduction of
> redundant queues doesn't present any new challenges.
>
>
> Regards,
>
> Matthias.
>
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