[rabbitmq-discuss] Flow control issue when shovelling messages between data centres

Simon MacMullen simon at rabbitmq.com
Wed May 15 15:37:30 BST 2013

On 15/05/13 10:48, SimonT wrote:
> I'd be interested though to understand better the relationship is
> between down-stream queue size / consumption rate and flow control.

A connection will go into flow control if it is trying to enqueue 
messages faster than the queue(s) can accept them....

> For
> example, if the consumer is not keeping up and the queue is growing,
> will this increase the chance of flow control at the publisher.

...and the amount of work done to accept a message is much higher if the 
message must go to disc. So if you're publishing persistent messages the 
cost should be constant, but if you're publishing transient messages 
there's a big step change in cost to accept a message when a queue gets 
big enough that RabbitMQ starts to page it out.

> Also
> what is the effect of TTL on the queue - e.g. will a shorter TTL result
> in less up-streamm flow control?

Only to the extent that it keeps such a queue shorter.

Cheers, Simon

Simon MacMullen
RabbitMQ, Pivotal

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