[rabbitmq-discuss] How to do blocking asynchronously with Pika? I want 1 message at a time and stop receiving until I'm ready again.

Thu Feb 21 18:11:15 GMT 2013

On 2/20/13 4:12 PM, "Matthias Radestock" <matthias at rabbitmq.com> wrote:

>Scott,
>
>On 20/02/13 23:27, Scott Chapman wrote:
>> After further exploring it appears that you do this:
>> Using the BlockingConnection:
>> Receive Message
>> Run Handler to process message which can immediately ACK the message.
>> When Handler returns, next message is received from RabbitMQ.
>>
>> Simpler!
>
>The above won't stop rabbit from sending one or more messages to the
>client (depending on the basic.qos prefetch setting). While the app
>won't get to the see these messages until the Handler returns, the
>messages will still take up buffer space at the client or in the
>network, and they will be unavailable to other consumers on the same
>queue.
>
>If that is not what you want then follow Michael's suggestion of
>cancelling the subscription. Or simply delay the ack until the app is
>ready to process the next message.

Mathias

I'd like to clarify some points here.

If 1st message arrives, I ack it, and I am processing it then 2nd message
arrives, it will be held _in_the_client_?
So if the client gets rebooted, the message will be lost?
It appears that I can set the basic.qos prefetch-count to zero to solve
this problem?

If I decide to cancel the consumer,  I assume the proper order of events
would be:

Enable Consumer
Receive message 1
Cancel Consumer
Ack Message
Process Message
-> back to Enable Consumer.

I think one would not want to ACK the message before canceling the
consumer because it might immediately dump another message into the
consumer?

Thanks for the tips,

Scott