[rabbitmq-discuss] Determining Cause of Flow-Control Invocation

Simon MacMullen simon at rabbitmq.com
Fri Oct 4 15:55:58 BST 2013

On 04/10/2013 3:40PM, Richard Raseley wrote:
> So, my question is - what other things can I look at to determine the
> cause of the invocation of flow control. Additional relevant information
> is as follows:

Each queue can only use 100% of one core, so it is possible to hit flow 
control without using 100% CPU of all cores (if everything goes through 
one queue).

Also: queues with transient messages can start to page to disc if there 
is any memory pressure. This is not very easy to observe in current 
releases (we aim to make it clearer), but you can look at 
backing_queue_status in rabbitmqctl and the HTTP API - if ram_msg_count 
+ ram_ack_count != messages then the queue is paging.

This is definitely an area where we aim to improve things. 3.2.0 will 
already make paging rather easier to observe and control.

Cheers, Simon

Simon MacMullen
RabbitMQ, Pivotal

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