[rabbitmq-discuss] Ack semantics in RabbitMQ

Tue Mar 17 11:11:15 GMT 2009

Eran Sandler wrote:
> Regarding the blocking "GET" commands, I read about Kesterl (in the link
> I gave below) and thought its an interesting approach to make pulling a
> bit more efficient instead of sending the "puller" back to a short sleep.

Another approach is to set the prefetch window to 1, and start a
consumer. If you really did only want a single message, you can cancel
the consumer before acking the message. Otherwise, when you ack it, the
server will send you the next waiting message if there is one.

  --> BASIC.QOS{ prefetch_count = 1 }
  --> BASIC.CONSUME
  <-- BASIC.CONSUME-OK
  ... wait for a message to arrive ...
  <-- BASIC.DELIVER
  --> BASIC.CANCEL
  <-- BASIC.CANCEL-OK
  ... processing of message ...
  --> BASIC.ACK

versus

  --> BASIC.QOS{ prefetch_count = 1 }
  --> BASIC.CONSUME
  <-- BASIC.CONSUME-OK
  ... wait for a message to arrive ...
  <-- BASIC.DELIVER
  ... processing of message ...
  --> BASIC.ACK
  ... wait for a message to arrive ...
  <-- BASIC.DELIVER
  ... processing of message ...
  --> BASIC.ACK
  ...

Regards,
  Tony
-- 
 [][][] Tony Garnock-Jones     | Mob: +44 (0)7905 974 211
   [][] LShift Ltd             | Tel: +44 (0)20 7729 7060
 []  [] http://www.lshift.net/ | Email: tonyg at lshift.net