[erlang-questions] How to handle a massive amount of UDP packets?

[Rapsey]

Do some profiling. cprof to start with. A simple:
cprof:start(),cprof:pause(),cprof:analyse().
cprof:stop().
while the server is running is often quite revealing.

You need to figure out if your CPU is spent on sending or on receiving.
One thing to keep in mind is that the erlang UDP socket code is not exactly
as optimized as it could be for sending. To send something over UDP it
would be really fast if you used a NIF that calls a write on the FD.


Sergej

On Sun, Apr 15, 2012 at 8:08 PM, John-Paul Bader <hukl@REDACTED> wrote:

> Dear list,
>
>
> I'm currently writing a bittorrent tracker in Erlang. While a naive
> implementation of the protocol is quite easy, there are some performance
> related challanges where I could use some help.
>
> In the first test run as a replacement for a very popular tracker, my
> erlang tracker got about 40k requests per second.
>
> My initial approach was to initialize the socket in one process with
> {active, once}, handle the message in handle_info with minimal effort and
> pass the data asynchronously to a freshly spawned worker processes which
> responds to the clients. After spawning the process I'm setting the socket
> back to {active, once}.
>
> Now when I switched the erlang tracker live the erlang vm was topping at
> 100% CPU load. My guess is that the process handling the udp packets from
> the socket could not keep up. Since I'm still quite new to the world of
> erlang I'd like to know if there are some best practices / patterns to
> handle this massive amount of packets.
>
> For example using the socket in {active, once} might be too slow? Also the
> response to the clients needs to come from the same port as the request was
> coming in. Is it a problem to use the same socket for that? Should I
> pre-spawn a couple of thousand workers and dispatch the data from the
> socket to them rather than spawning them on each packet?
>
> It would be really great if you could give some advice or point me into
> the right directions.
>
> ~ John
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