[rabbitmq-discuss] auto-delete exchange kills connections on consumer close?

[Emile Joubert]

Hi Keith,

On 06/12/11 06:00, Keith Irwin wrote:
> Folks--
> 
> I'm using RabbitMQ (2.7.0 all around + java with Clojure) to send small
> little status messages around here and there. It works great for that.
> Because I don't care if these messages get dropped if, say, RabbitMQ
> goes down, or if some client messes up here or there, I want to keep
> everything temporary. When all the clients are stopped, I'm thinking,
> RabbitMQ should be back to its default state.
> 
> So, when I use exchangeDeclare, I set auto-delete for the exchange to
> true. Here are my expectations:
> 
>  - When there are no more clients consuming or publishing to that
> particular exchange, it'll disappear.

Your description applies better to queues than exchanges. When the last
client consuming from an auto-delete *queue* unsubscribes, the queue
auto-deletes.

An auto-delete exchange self-destructs when the last binding is removed.
(If you are using exchange-to-exchange bindings then the exchange must
be the source.) The binding might be removed as the result of an
auto-delete queue disappearing, which in turn might happen as the result
of a consumer unsubscribing, but that is incidental.

Remember that consumers don't consume from an exchange directly.

> What ACTUALLY happens is that when the first user of that exchange is
> closed (by calling close on a channel), the exchange is deleted, and all
> other users of that exchange get disconnected.

As described earlier, a subscriber that unsubscribes can cause a cascade
of auto-deletions to occur that removes an exchange. Publishers that
attempt to publish to an absent exchange will then fail. Is this what is
happening?

> Is this a bug?

If my interpretation is correct then no.

> Should you always set autoDelete to false if there is ever going to be
> more than one client using an exchange? And isn't there always going to
> be another client using that exchange given there's no point in using an
> MQ system otherwise?

Don't use auto-delete exchanges if you will have more than one publisher
for that exchange. There are use-cases where an exchange has a single
publisher.

Also consider whether the default exchange is sufficient for your needs.



-Emile