RabbitMQ difference between exclusive and auto-delete?

The "RabbitMQ in Action" book on page 19 gives these descriptions of exclusive and auto-delete:

> exclusive - When set to true, your queue becomes private and can only > be consumed by your app. This is useful when you need to limit a queue > to only one consumer. > > auto-delete - The queue is automatically deleted when the last > consumer unsubscribes. If you need a temporary queue used only by one > consumer, combine auto-delete with exclusive. When the consumer > disconnects, the queue will be removed.

But as far as I can see when using exclusive, auto-delete is redundant. Only exclusive is needed. The RabbitMQ tutorial seems to say that is the case

> ...once we disconnect the consumer the queue should be deleted. There's > an exclusive flag for that:

result = channel.queue_declare(exclusive=True)

There is no mention in that tutorial about auto-delete and sudo rabbitmqctl list_bindings seems to indicate that the queue is in fact deleted after the receiver goes away.

Well, it is true that exclusive queues will auto-delete when the consumer disconnects (see the documentation pasted below). However, there are cases when you want queues to be non-exclusive, yet still auto-delete (for example, if I want to add another consumer).

> exclusive > > Exclusive queues may only be accessed by the current connection, and are deleted when that connection closes. Passive declaration of an exclusive queue by other connections are not allowed. > > auto-delete > > If set, the queue is deleted when all consumers have finished using > it. The last consumer can be cancelled either explicitly or because > its channel is closed. If there was no consumer ever on the queue, it > won't be deleted. Applications can explicitly delete auto-delete > queues using the Delete method as normal.

Personally, I prefer to use neither of these parameters, instead opting for the RabbitMQ queue expiration parameter, which is better if I have a consumer disconnect and then re-connect immediately (or a short time) later; messages are not lost in this case. But, of course it all depends upon your application and requirements.

In contrast to what theMayer described, my testing showed that there is a difference in behavior when auto-delete is toggled while exclusive is set to true.

If auto-delete is set to false, the queue is indeed tied to the connection and will disappear when the connection is terminated.

If auto-delete is set to true, the queue will be deleted after the last consumer is cancelled.

There is a difference between a connection and a consumer. You can be connected, but not consuming a given queue. If you need the queue's lifecycle to be tied to your connection rather than to whether or not you're actively consuming it, set auto-delete to false in conjunction with exclusive=true.