[rabbitmq-discuss] Prefetch fields in management UI

Wed Apr 23 09:08:18 BST 2014

On 23/04/2014 00:21, Ben Hood wrote:
> So qos does not appear to
> take effect if the command is submitted after the call to subscribe to
> a queue, with in the context of a single channel. So to fix this
> issue, all I needed to do is to make sure that setting the prefetch
> happens before subscribing to a queue. I never realized that egress
> qos is order dependent - I had just assumed that that it is a
> changeable value within the context of the limiter.

Note that the semantics of qos have changed in 3.3.0:

http://www.rabbitmq.com/consumer-prefetch.html

Per-consumer prefetch will be fixed at the moment the consumer is 
created. Per-channel prefetch can be changed after the fact, as before. 
But it was never a great idea to do that since if you set qos after 
consuming then the broker can deliver as many messages as it wants in 
between the two commands, which is unlikely to be what you want.

Cheers, Simon