[zeromq-dev] Reduce latency on Pub-Sub Broker

[Pieter Hintjens]

Robert,

First, try some tests in plain C (using the low level API or CZMQ), to
make sure that it's not the C# binding adding latency.

There are command-line test programs you can use (perf/local_lat,
perf/remote_lat).

Secondly, if the latency increases when you send messages faster,
there is something bogus happening. 0MQ will normally batch small
messages which reduces latency if you send larger volumes. The main
reason for setting a HWM is if your subscriber or network is too slow,
and you need to guard against memory exhaustion.

It sounds like you have a CPU contention issue. How many cores on your
box? What kind of network?

-Pieter



On Tue, May 29, 2012 at 10:26 AM, Robert Evans
<zwergzebra at googlemail.com> wrote:
> Hello everyone,
>
> I am currently developing a Publish-Subscribe broker using the C# binding
> clrzmq v. 2.2.3. My operating system is Windows 7 Prof. and my system is a
> Intel i7 with 16 GByte RAM.
>
> The broker works without any problems, I have added one publisher and one
> subscriber and get message rates about 250 000 - 150 000 msg/second when
> sending 10 byte messages on localhost. The broker simply forwards the
> messages from the publisher to the subscriber, no big magic there.
>
> My problem is the increasing latency when sending many messages at short
> time. When I only send one message and sleep for one millisecond the latency
> is < 1ms, but the message rate drops to 9000 msg/s. When I'm sending
> messages straight without sleeping at ~ 200 000 msg/s, the latency increases
> with the number of messages sent. I set the HWM on the broker for the pub
> and sub socket to 500, which seems to narrow the latency to 10 - 20 ms. This
> is okay, but a value between 1 and 3 ms would be even better.
>
> Is there a way to reduce it even more? I don't really need the queuing of
> messages with the HWM; I would rather like to drop messages instantly
> instead of queuing as low latency is very important in my project (but I
> still need a message rate about 100 000 msg/s). As to say shortly: Better
> drop some messages for lower latency, instead of buffering them.
>
> It would be great if someone has an idea or already has some experience with
> tweaking the latency. Thank you!
>
> Regards,
> Robert
>
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