[rabbitmq-discuss] Run RabbitMQ server with N scheduler threads

[Katerina Roukounaki]

On 19 March 2012 16:27, Simon MacMullen <simon at rabbitmq.com> wrote:

> On 16/03/12 17:28, Katerina Roukounaki wrote:
>
>> Since the RabbitMQ server is an Erlang application, I wanted to see
>> whether it runs faster as I increase the number of scheduler threads in
>> the Erlang VM that runs it (+S option of the erl program).
>>
>> For this purpose, I wrote a simple benchmark (in Erlang) that spawns P
>> producer and P consumer processes and creates P queues. The i-th
>> producer sends M messages to the i-th queue and the i-th consumer waits
>> to receive them. My benchmark uses native Erlang messaging for sending
>> and receiving messages.
>>
>
> So just to be clear: you are using the direct client? Or something else?


Yes, I'm using the direct client.

>
>
>  I attach the results I get when I run the benchmark with P=M=1000 on a
>> machine with 16 cores and assign 1, 2, …, 16 scheduler threads to the VM
>> that runs the RabbitMQ server.
>>
>> As you can see, things get better up to 6 schedulers, but with 7 or more
>> schedulers it seems that there is no further speedup.
>> Do you have any idea why this is happening?
>>
>
> At a guess: hyperthreading? I assume your machine is 8 physical cores and
> 16 hyperthreads. In which case the extra cores presented by hyperthreading
> are presumably not helping much.
>

No. The machine has 16 physical cores. This is the first reason I had not
expected the results I got.


>
> But I'm not an expert on the Erlang scheduler.
>
>
>  Is there some kind of synchronization among the processes that the
>> RabbitMQ server spawns that explains it or should I look for bugs in my
>> benchmark?
>>
>
> All your producer-queue-consumer chains are independent, right? So it's:
>
> P1 -> Q1 -> C1
> P2 -> Q2 -> C2
>
> ?
>
> If so then there's no synchronisation between the processes done by
> RabbitMQ.
>
> Exactly. And this is the second reason I had not expected the results I
got.


> You might want to play with the other scheduler options. +sbt looks
> particularly interesting...
>
>
I'll try that and I'll come back with fresh results.

Thanks,

Katerina


> Cheers, Simon
>
> --
> Simon MacMullen
> RabbitMQ, VMware
>
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