[rabbitmq-discuss] rabbitmq-ha-test setup

Mark Steele msteele at beringmedia.com
Fri Jul 29 14:57:07 BST 2011

Hope springs eternal. I'm looking forward to the 'linear scale full blown
HA' feature that must be deep down somewhere in the roadmap.

Still, mirrored queues will be a welcome addition.



On Fri, Jul 29, 2011 at 9:47 AM, Matthew Sackman <matthew at rabbitmq.com>wrote:

> On Fri, Jul 29, 2011 at 09:25:55AM -0400, Mark Steele wrote:
> > Out of curiosity, does the master election occur on a per queue basis or
> is
> > it cluster-wide?
> Per queue. And it's not really master election. It's simply a list which
> is appended to when new slaves join and removed from as people die. It's
> done in such a way as to ensure that when the master dies, the new
> master is the most likely to have been in the same state as the old
> master.
> > Mirrored queues are great, however there is still the thorny issue of
> being
> > limited to the throughput of the master when you've got one queue that
> has
> > lots of messages in it.
> >
> > If the election process operates on a per queue basis, then it would be
> > possible to declare multiple queues to the same exchange and effectively
> get
> > load balanced usage of the cluster with all the goodness of high
> > availability.
> Slaves have to do almost as much work as the master, and there's much
> greater communication overhead. Thus even though the design is async and
> has been substantially tuned, you will find mirrored queues perform less
> well than non-mirrored queues. At the end of the day, you just have to
> do quite a lot more work and that'll take more time.
> Matthew
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