[Twisted-Python] Multi-reactor architecture

[Reza Lotun]

> Once there is a Site that serving many clients and
> reactor.listenSSL(), for example, that actually serving many TCP
> connections and all these going through TwistedGateway, my logic,
> please correct me if I wrong, says at some point there will be a limit
> on concurrent TCP connections, so how is it solved with Twisted?

That's a good question and I'm not sure if there's a definite answer
to this (as far as I know). I think it depends on your application -
for example, if your server is performing a big computation then on
average client connections will last longer, meaning you'll have more
concurrent connections.

The best way to determine this is to *measure* it - for example, you
can do a load test with httperf and ramp up connections until this
start to break or become unresponsive.

You can mitigate the situation by tuning your platform a bit (assuming
you're using linux)
- use the epoll reactor, which is high performance
- make sure the number of open file descriptors is set to something
high (and *not* 1024) - see `ulimit -a`
- make sure you tune your tcp settings - see /etc/sysctl.conf, namely
fs.file-max and various net.ipv4 settings (google is your friend on
the best settings, coupled with testing)

Cheers,
Reza

-- 
Reza Lotun
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