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Date: Thu, 22 Nov 2007 12:43:25 +0300
From: Andrew Pantyukhin <infofarmer@FreeBSD.org>
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Subject: lightly loaded php+mysql - high syscall/csw rates
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We have a php+mysql web server. It serves 15-20 http requests per
second, resulting in 100-200 sql qps. But according to vmstat(1),
it all peaks at over 500k syscall/s and 100k cswitch/s. The peaks
are quite frequent, even at this load. During the peaks top(1)
shows 30-40k VCSW for mysql and around 1k vcsw for two php-cgi
worker processes. IVCSW is relatively very low for all processes.

This is a 4-core Opteron HP DL145 G2 server running 6.2/amd64
generic+quota. I'm considering a switch to 7.0.

During peaks user/system/idle in top(1) is 20/30/50.

The question is - is the syscall and csw rates normal or should I
be trying to tune mysql and php more agressively? I'm not hungry
for performance (haven't hit the limit yet), but a couple of days
ago the server stopped responding until a cold reboot (which is
another story) - and now I'm paying closer attention to its
vitals.