[rabbitmq-discuss] Ensuring low latency for publishers

Tue Feb 28 05:41:22 GMT 2012

Hello.
I had the same situation. Web application written in java that
publishes on each request and needs to respond fast (even with 50x
error). Rabbitmq throttling once halted all connected web frontends
causing whole cluster failure.
Then I used a separate publishing thread with blocking queue and
single lock contention wasn't a problem for me. But publishing rate on
a single machine was quite low about hundred/s.

On Fri, Feb 24, 2012 at 3:20 PM, Simon MacMullen <simon at rabbitmq.com> wrote:
> On 23/02/12 20:27, Eric wrote:
>>
>> Well... I would find it useful.  And the person in the thread I linked
>> to would have found it useful as well.
>
>
> Sure, I'm trying to gauge how widespread such a demand is. It looks like we
> could plausibly do something in this direction.
>
>
>> It's pretty tough to go into a production environment with the
>> statement "Publishing should be fast unless the broker is throttling.
>> If the broker is throttling we won't be able to tell, we don't have a
>> good way of knowing beforehand, and we don't know how long the threads
>> will be blocked".  It's useful in any case where an application would
>> rather not publish the message rather than waiting to publish it
>> indefinitely.
>
>
> Yeah, the problem is that we've historically optimised for Never Throwing
> Away Messages Ever Ever...
>
>
>> The net result is that a struggling broker will cause a chain
>> reaction; publishers will block indefinitely, which may bring the
>> publishing application to a halt.  In that case I'd like to abandon
>> the publishing process, but it's quite impossible at that point - it's
>> too late, the broker is already throttling, and there's no timeout.
>> The thread could block for seconds, or more.  I'm concerned about not
>> throwing the message away, but I'm more concerned about being able to
>> isolate services from RabbitMQ broker events.
>
>
> If it's any consolation the flow control stuff that's coming in 2.8.0 will
> make it much harder to make the memory alarm go off, so blocking for seconds
> should be much less likely.
>
>
>> One more question along this line.  The flow control document says "By
>> default, when the RabbitMQ server uses above 40% of the installed RAM,
>> it raises a memory alarm... Connection heartbeat monitoring gets
>> disabled too."  If I set up a connection heartbeat on the shared
>> connection, will the heartbeat detect a broker alarm that exceeds the
>> interval and disconnect?  A disconnect would terminate the publisher
>> channels and free things up.
>
>
> No - the whole point of disabling heartbeats is to make sure connections
> stay up when this happens...
>
>
> Cheers, Simon
>
> --
> Simon MacMullen
> RabbitMQ, VMware
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