[rabbitmq-discuss] Ensuring low latency for publishers

Tue Feb 21 18:11:43 GMT 2012

Thanks for the quick reply.

> No. Well, there are various ways you can force it to, but by default
> it's async.

Awesome!  Great that publishing is async.

> Well, you still have the one way network latency - or do you mean from
> the point of view of the client?

Right, sorry.  I mean ~0ms from the point of view of the client.  I
don't care too much about message latency from publisher to the
eventual consumer, just so long as the publisher doesn't experience
any delay.

> Maybe we should call it TCP flow control? But yes, if your broker is out
> of memory, publishing will block until the broker is ready to read again.
>
> Would you rather drop the message at this point?

"TCP flow control" got me to a helpful Wikipedia article much faster,
so maybe that's better.  :)  I would rather drop the message at that
point.  Ideally there'd be some timeout to specify there... if I've
been blocked for a few ms, it's time to give up.  But publisher
throttling is supposed to be transparent to the publisher, right?

On Feb 21, 9:58 am, Simon MacMullen <si... at rabbitmq.com> wrote:
> On 21/02/12 17:51, Eric wrote:
>  > First, does publishing
>  > a message require a roundtrip to the broker?
>
> No. Well, there are various ways you can force it to, but by default
> it's async.
>
>  > so I'm assuming publishing is essentially a 0ms
>  > operation
>
> Well, you still have the one way network latency - or do you mean from
> the point of view of the client?
>
>  > but I want to be sure.  Second, if the broker is throttling
>  > via "TCP backpressure" (which I'm having a hard time finding a good
>  > definition for) will that increase publisher latency?
>
> Maybe we should call it TCP flow control? But yes, if your broker is out
> of memory, publishing will block until the broker is ready to read again.
>
> Would you rather drop the message at this point?
>
> Cheers, Simon
>
> --
> Simon MacMullen
> RabbitMQ, VMware
>
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