[rabbitmq-discuss] Push to back of Queue on NAck

Fri Jul 26 14:18:40 BST 2013

On 26/07/13 13:25, Will Hughes wrote:
> Scenario:
> I'm processing messages from a queue with confirmation required.
> The number of messages relative to the consumption rate can be quite
> high at times. In excess of hundreds of thousands of messages, with
> consumption rate in the low hundreds per second range.
>
> Sometimes we have to abandon processing a message for some transient
> reason (eg: external resource is locked/unavailable), and so we send a
> NAck.
> At the moment, RabbitMQ will immediately redeliver that message to any
> of the consumers. If the transient condition is still in place, we can
> potentially get into a tight loop where we're constantly consuming the
> same message(s) hundreds of times per second.
>
> For our scenario, we *can* duplicate the message, send it to the
> exchange/queue, and Ack the original.

The problem here is that with a short queue you still end up in a tight 
loop.

> Something I thought might be a bit nicer is if we could have an option
> to have RabbitMQ put the message at the back of the queue. Depending on
> the size of the queue and our processing rate, this might give us an
> easier way to try other messages in the queue first.

This suffers from the same problem.

> Another option I was thinking of to enforce more a delay was to see if I
> could chain together two queues using dead-letter-exchange settings:
>
> Queue A, no TTL, DLX=Exchange B (with Queue B bound to it).
> Queue B, ttl of (x) seconds, DLX= Exchange A (with Queue A bound to it).
>
> When we NAck the mesage from Queue A, we set requeue=false.
>
> I've not seen much discussion so far on whether it's sane to hook up two
> queues/exchanges in a loop like this.

Yep, that makes perfect sense and should work well.

Matthias.