[rabbitmq-discuss] Consumer stop to receive messages but continue listening queue problem.

Wed May 19 16:44:52 BST 2010

Mathias,

On Wed, May 19, 2010 at 1:20 AM, Matthias Radestock
<matthias at rabbitmq.com>wrote:

> Gustavo,
>
>
> Gustavo Aquino wrote:
>
>> We put test to run for 1 hour, and monitoring queue size with rabbitmqctl
>> list_queues, all the time list have 0 size, so consumer are getting all on
>> the fly, and now we stop publisher and here is the BIG PROBLEM, consumer
>> continue to consume messages from queue... and it's remain for 20 minutes
>> after stop publisher......
>>
>> If we stop consumer we can see the queue growing for long time...,
>> therefore looking for it's we can conclude that our consumer are 20 minutes
>> late behind publisher and it's a f... problem last message from publisher
>> will be received by consumer just 20 minutes after.
>>
>
> How are the messages being consumed? Using basic.consume? If so then the
> above observation is consistent with messages getting buffered in the
> network and/or consumers.
>
> Yes, basic consumer have other best way ? If I drop consumer queue continue
to grow my friend, withour any consumers or publisher queue size continue to
grow for 20 minutes after stop in this scenario.

> How are you monitoring the queue lengths? The default output of
> 'rabbitmqctl list_queues' will give a figure that is the sum of ready,
> unacknowledged and uncommitted messages. You can get a more detailed
> breakdown with s.t. like 'rabbitmqctl list_queues name messages_ready
> messages_unacknowledged messages_uncommitted' - see
> http://www.rabbitmq.com/admin-guide.html#list_queues.
>

Thanks, I know this extra commands in rabbitmqctl list_queue, now we are
using a lot of them.

>
> If my above analysis is correct then for the total to be zero the clients
> would have to be consuming messages in no-ack mode, since otherwise the
> messages_unacknowledged count would go up. Are they?
>
>
Rabbitmqctl just show message_ready size, other parameters like
messages_unacknowledge and etc all the time are 0.

>
> So can anyone help me ? Its's a common problem in Rabbit ? anybody here
>> have this same problem ? We have talked about a possible exchange buffer
>> cause and etc in this way, but to be sincerely in my thoughts ~3000 m/s is a
>> bit easy to be processed for one message server.
>>
>
> It looks like rabbit is handling the load just fine, but the consumers are
> struggling to keep up and are just buffering the messages. This can happen
> easily if the consumer code is employing s.t. like the QueueingConsumer in
> our Java client library -
> http://www.rabbitmq.com/releases/rabbitmq-java-client/v1.7.2/rabbitmq-java-client-javadoc-1.7.2/com/rabbitmq/client/QueueingConsumer.html
>
> But it can also happen just through buffering in the network layers.
>

It´s happened with consumers and without consumer... I don´t think that it
as network problem.

>
> To avoid a large backlog building up, probably the easiest solution is to
> set a prefetch limit with basic.qos. But for that to be effective the
> consumers must be consuming in ack mode.
>
>
Thanks.

>
> Regards,
>
> Matthias.
>
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