[rabbitmq-discuss] Why is the queue created on the consumer's side?

Mon Feb 13 11:09:33 GMT 2012

thanks a lot Alexandru, you did help me!

Alexandru Scvorţov wrote:
> 
> Hi,
> 
>> I've understood from the tutorials that the producer doesn't send any
>> message directly to a queue, and that quite often doesn't even know if a
>> message will be delivered to a queue.
> 
> Correct.  It can use mandatory and immediate delivery modes to check if
> the message has reached any queues, though.
> 
>> Does queue declaration means queue creation? If yes, I think that it is
>> quite strange to create a queue on the consumer's side in real
>> applications.If no, where is the created?
> 
> Queue declaration is an idempotent queue-creation.  It's more like an
> assertion that the queue exists (after the queue.declare, you *know* the
> queue exists).  So, you can declare a queue multiple times, but it will
> only be created once.
> 
> Who should declare the queue depends from application to application.
> For instance, in a work-queue scenario (where a producer enqueues tasks
> for workers to execute), the producer should declare the queue (so that
> tasks are queued even if there aren't any active workers).  In many
> pub-sub scenarios, where consumers subscribe to events from a producer
> (and old events are not interesting), the consumers would declare queues
> (probably, one each).  In many other cases, both the consumer and the
> producer would declare the queue (the producer to ensure that messages
> aren't lost, and the consumer so that it can start consuming from the
> queue even if the producer hasn't come online to declare the queue yet).
> 
> Hope this helps.
> 
> Cheers,
> Alex
> 
> On Sun, Feb 12, 2012 at 05:32:36AM -0800, Bamboula wrote:
>> 
>> Hello all,
>> 
>> I've understood from the tutorials that the producer doesn't send any
>> message directly to a queue, and that quite often doesn't even know if a
>> message will be delivered to a queue.
>> 
>> In the third tutorial (Publisher/Subscriber), the queue is declared on
>> the
>> consumer's side. I think that's for simplicity reasons in this particular
>> example (since the number of consumers is equal to the number of queues). 
>> Does queue declaration means queue creation? If yes, I think that it is
>> quite strange to create a queue on the consumer's side in real
>> applications.If no, where is the created?
>> 
>> I would appreciate if someone could give me some information.
>> 
>> Thanks a lot,
>> 
>> Bamboula 
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