[rabbitmq-discuss] Durable Queue

Matthew Sackman matthew at rabbitmq.com
Mon Oct 17 23:37:29 BST 2011

On Mon, Oct 17, 2011 at 12:57:49PM -0700, Gil Strauss wrote:
> If I configure durable mirror queue, does any incoming message is
> being written on the master and mirror disks?

No, not on disk. Replication is largely done in a safe but asynchronous
way - the master can get "ahead" of the slaves, but only in such a way
that if the master dies and the slaves then take different decisions, no
observable difference is possible anyway.

> Another question - is it possible that a subscriber that configured to
> send an acknowledgement will receive the same message twice?

Yes. Given there is no "ack" to an "ack", the ack can always be lost in
flight. Active/active HA actually extends the flight-time of an ack and
presents more possibilities of loss of ack. Thus as usual, you should be
prepared to deal with duplicates on consumers.


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