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From Brian Behlendorf <br...@hyperreal.org>
Subject strange performance delays
Date Fri, 31 Oct 1997 03:52:22 GMT

I'm running a benchmarking program against an apache 1.3 server (actually,
against Hyperreal itself, during off hours :) and there are some things I'm
seeing which give me, uh, cause for concern.  I'm going to an SSI page
which involves one search for an htaccess and I've got followsymlinks on.
I'm going to the exact same page, so it should be at the top of the disk
cache.  I'm getting roughly 50 per second, with latencies around 15-20 ms
on average (from a machine over a packet-filtering firewall, which added
about 4 ms based on ping).  However, once every 200 requests or so, it
takes well over a second to service the page.  Once every 1000 requests, I
see an even larger hit; the largest I've see was 46 seconds (!!!).

Now, I accept the chaos of a multiuser system, especially hyperreal, where
a qmail delivery process to a big list can fork() 256 separate deliveries
in 3 seconds.  :)  I also accept the possible error within the firewall
between us.  But can anyone think of any part of apache which could cause a
gap like this?

By the way, the benchmarking program was opening several parallel threads;
the more parallel threads, the greater the frequency of these strange delays. 

I suppose a fork() could take an arbitrary long time.  But 46 seconds?

Anyways, any thoughts would be cool.

	Brian


--=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--
"it's a big world, with lots of records to play."-sig   brian@hyperreal.org

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