[rabbitmq-discuss] RabbitMQ scaling with OpenStack

Thu Jan 24 21:38:09 GMT 2013

Ray,

On 23/01/13 16:43, Ray Pekowski wrote:
> 4) The OpenStack RPC producers re-declare the queues and exchanges upon
> which they send messages.  I say re-declare, because under normal
> circumstances in the OpenStack implementation, the consumers exist
> before the producers and so have already declared/created the exchanges
> and queues.  I think this is done in case an RPC call is made to a
> service that isn't up at the time.  I wonder that is a good practice,
> but I may be missing some other reason for it.  I might play around with
> prototyping a removal of the producer side re-declares.

{queue,exchange}.declare when the resource already exists are quite 
cheap. However, the latency of the associated network roundtrip can 
badly affect performance. Unless you set the nowait flags, thus 
suppressing the response and making the commands asynchronous. Even then 
though these are not commands you'd want to send for every message.

Regards,

Matthias.