[rabbitmq-discuss] Vanishing of persistent messages on durable, auto-deleting queue with dead-lettering

Sun Jul 1 19:23:14 BST 2012

Ernest,

On 29/06/12 17:27, Ernest Staszuk wrote:
> After disconnecting a client from durable, auto-deleting queue with
> dead-lettering-exchange I would expect passing all messages to dead
> letter exchange and then deleting queue. But surprisingly for me
> queue was deleted and messages just vanished into limbo.

That's the defined behaviour. From 
http://www.rabbitmq.com/extensions.html#dead-letter-exchanges
<quote>
A message is dead-lettered when any of the following events occur:
- The message is rejected (basic.reject or basic.nack) with 
requeue=false; or
- The TTL for the message expires.
</quote>

> Is this behavior desirable? Why?

We deliberately kept the set of operations susceptible to dead-lettering 
small, to avoid unintended consequences. It is possible that actions 
like auto-deletion, queue lease expiry, explicit deletion and purging 
should all trigger the dead-letter mechanism, but I'd like to see 
compelling use cases first before making such a change.

> How should I get around this problem? I thought about declare queue
> as non auto deleting and making own monitoring daemon, which could
> handle cleaning queues without consumers. Is there any simpler way of
> achieve my goal?

Perhaps a combination of queue leases and ttl would work. The former has 
the additional advantage of allowing the system to mask temporary 
consumer and connectivity failures.

Regards,

Matthias.