[rabbitmq-discuss] Count Constraining Q

Emile Joubert emile at rabbitmq.com
Wed Nov 23 10:55:21 GMT 2011

Hi Marc,

On 23/11/11 00:15, Marc Dworkin wrote:
> My Question is this: I would like to be able to specify the number of
> instances of a particular job running at any given time.  Currently I

If I understand your question correctly it could be rephrased as "how
can I limit the number of unacknowledged messages in a queue with
multiple consumers?"

If you had a way of limiting the number of consumers to the queue to the
desired number then that can limit the number of unacknowledged
messages. Declaring or redeclaring a queue returns the current consumer
count. This number could be used to determine whether a queue is allowed
any more consumers. Each consumer should only be allowed one
unacknowledged message.

It is possible to limit the number of unacknowledged messages held by a
single consumer, using the basic.qos method. A single specialised
consumer that used the desired QoS value, and redistributed jobs to
workers might also solve the problem.


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