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From "Pascal Felber" <Pascal.Fel...@eurecom.fr>
Subject mod_perl performance question
Date Thu, 08 Apr 2004 15:48:53 GMT
We have noticed some "strange" behavior when stress-testing one of our
perl modules and we haven't managed to find an explanation or workaround
in the mod_perl documentation. We have reproduced this problem with a
minimal module, installed as a PerlResponseHandler, that simply sends am
HTTP 302 redirection message to the client. The server is a P4@1.5GHz
512MB, running linux 2.4.18-3, Apache 2.0.48, and mod_perl 1.99_08. We
have run benchmarks using the `siege' application with an increasing
number of clients and we have measured the latency of every request.

I have put a graph online at http://www.eurecom.fr/~felber/mod_perl.gif
that illustrates the problem. The response time of the server is roughly
constant but we observe some pretty high spikes in the latency every 30
seconds or so, as if the server was interrupted for a short period of
time (approx. 300 ms). The delay of 300 ms seems very high for tasks
like shared memory accesses or garbage collection, given that our test
module does almost nothing. When running the same test using mod_alias
for redirections, there are no such spikes; so it really looks like they
are due to mod_perl rather than the OS, Apache, or the network. There
might be an obvious explanation but we have limited expertise with
mod_perl and we would very much appreciate some help from other users on
this list.

Thanks,
Pascal Felber


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