Re: wish for an advice

On fre, 2007-08-03 at 15:37 +0200, Jiri Kuthan wrote:

> I'm wondering if you could do me a massive favor and exchange some experience you
> might have gathered with building squid regarding TCP scalability.

We can try..

> I've been writing a SIP proxy server, SER (www.iptel.org/ser), which typically operates
> in UDP mode. Now in the IETF, TCP is gaining more momentum. SER supports it but compared
> to UDP it scales rather poorly -- at the moment we can't get more than 50k connections
> out of it.

The primary thing to keep in mind is to make use of a decent event
notificatoin mechanism, i.e. epoll/kqueue/devpoll. Without it
performance will quickly suffer when the amount of connections
increases.

To make life easy one may use libevent, which provides all the needed
framework.

When using a good event notification the performance is again more
related to the amount of messages one has to process and not related to
the amount of concurrent connections.

> Could you share with me, how many TCP connections can squid handle, if you have any
> performance measurment results, tuning tips, etc?

Unlike SIP HTTP is still dominated by relatively shortlived connections,
so we don't get that many concurrent connections. A very buzy server is
more in the range of 5-10K connections.

But have done lab tests with several hundreds of thousand idle
connections, to verify that the event notification works. It does, but
Squid's connection oriented buffer management makes it consume quite a
bit of memory...

Regards
Henrik