Messages in this thread | | | Date | Thu, 9 Jul 1998 15:28:42 +0100 | From | "Stephen C. Tweedie" <> | Subject | Re: File-descriptors - large quantities |
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Hi,
On Wed, 08 Jul 1998 13:38:36 +0800, "Michael O'Reilly" <michael@metal.iinet.net.au> said:
> If you're even coming close to using 3000 FDs then I can guarentee > that your disk thruput is maxed out for squid 1.1.
Michael,
There was an interesting paper on this at the recent Usenix. A large proxy server had been profiled and they showed an average of 50 hot connections present at any time, and *750* cold (slow) connections, at a rate of 220 new connections per second. The cold connections were purely a result of WAN-level timings; under lab conditions all connections were serviced pretty rapidly, but on the internet, enough connections go really slowly to contribute a lot to mean connection lifetimes. They had a median connection lifetime of 250ms and a mean of 2.5 seconds.
This is a real problem: you don't have to have a massively busy server, just a server requesting items from a slow domain, for the number of outstanding connections at a time to grow enormously. (The Usenix paper was explicitly dealing with slow select() and get-new-fd handling in the kernel, btw.)
--Stephen
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