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

[Tom Anderson]

On 26/07/13 14:18, Matthias Radestock wrote:
> On 26/07/13 13:25, Will Hughes wrote:
>
>> 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.

Implemented exactly as described there, it yields an infinite loop for 
unprocessable messages. You might therefore also want to keep a count of 
the number of processing attempts in a header on the message, and more 
thoroughly reject messages which reach some maximum number of attempts. 
I think you could do the final rejection by setting a routing key on the 
message when you reject it for the last time, and having exchange B be a 
direct exchange which routes to either queue B or some final deadletter 
queue.

If you want exponential backoff in the retries, then life gets more 
complicated (multiple timeout queues, selected between by a routing key 
set by the consumer of A?). We are currently pussyfooting around this 
issue at my company. I will report back here if we ever implement a good 
solution!

tom

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Tom Anderson | Developer | +44 20 7826 4312 | timgroup.com 
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