[rabbitmq-discuss] Latency of publish confirm

[Pierpaolo Baccichet]

Found something interesting. I tried to temporarily disable the policy for
mirroring of my test queue and now I am consistently getting 7/7.5
milliseconds latency. Seems like the issue is triggered by the mirroring of
the queue.

Pier


On Tue, Dec 4, 2012 at 7:11 AM, Pierpaolo Baccichet
<pierpaolo at dropbox.com>wrote:

> Hello Matthias,
>
> Thanks for your quick response!
>
> I double checked the code to make sure that I am not marking messages as
> persistent and indeed that's the case. The queues and the exchanges are
> marked as durable but the individual messages I send are not setting the
> delivery_mode=2.
>
> I am a little skeptical the issue here is sync on disk because adding
> producers does not change the behavior. I ran a test with 5 producers
> sending 10 messages per second each and I am still seeing exactly the same
> results. Each producer observes latencies that are multiple of 31
> milliseconds (though based on wireshark capture, this latency seems to be
> dominated by the 25 milliseconds we see in rabbitMQ side). Example output
> of what I am seeing on the producer side is below:
>
> 1354633782.0697601 - completing send 15 took 63.736915588378906
> 1354633782.233757 - completing send 16 took 63.80009651184082
> 1354633782.3976469 - completing send 17 took 63.717842102050781
> 1354633782.5615449 - completing send 18 took 63.707828521728516
> 1354633782.725692 - completing send 19 took 63.929080963134766
> 1354633782.8579049 - completing send 20 took 31.997919082641602
> 1354633783.0219419 - completing send 21 took 63.837051391601562
> 1354633783.1538589 - completing send 22 took 31.718969345092773
> 1354633783.285862 - completing send 23 took 31.77189826965332
> 1354633783.4498329 - completing send 24 took 63.776016235351562
>
> Also, in my previous email I forgot to specify my environment. I am
> running on rabbitMQ 3.0 Erlang R15B02. Python and pika 0.9.8 on the
> client side
>
> Pierpaolo
>
>
> On Tue, Dec 4, 2012 at 1:22 AM, Matthias Radestock <matthias at rabbitmq.com>wrote:
>
>> On 04/12/12 08:55, Matthias Radestock wrote:
>>
>>> I am guessing your messages are marked as persistent. The 25ms is indeed
>>> an aggregation interval, but for the disk (in particular fsyncs) rather
>>> than the network.
>>>
>>
>> However, fsyncs also happen when queues and the storage sub-system go
>> idle, so the interval only kicks in when the system is busy (thus ensuring
>> that fsyncs aren't delayed indefinitely).
>>
>> So I am pretty sure what you are seeing is simply the cost of performing
>> an fsync per message. There's nothing that can be done about that except
>> buying faster disks / switching to SSDs.
>>
>> Regards,
>>
>> Matthias.
>>
>
>
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