From: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Qingqing Zhou <zhouqq@cs.toronto.edu>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Test request for Stats collector performance improvement
Date: Fri, 16 Jun 2006 20:14:47 +0200
Message-ID: <4492F517.7060405@kaltenbrunner.cc> (raw)
In-Reply-To: <200606161624.k5GGO3N03466@candle.pha.pa.us>
References: <200606161624.k5GGO3N03466@candle.pha.pa.us>
Bruce Momjian wrote:
> Stefan Kaltenbrunner wrote:
>> Bruce Momjian wrote:
>>> OK, based on reports I have seen, generally stats_query_string adds 50%
>>> to the total runtime of a "SELECT 1" query, and the patch reduces the
>>> overhead to 25%.
>> that is actually not true for both of the platforms(a slow OpenBSD
>> 3.9/x86 and a very fast Linux/x86_64) I tested on. Both of them show
>> virtually no improvement with the patch and even worst it causes
>> considerable (negative) variance on at least the Linux box.
>
> I see the results I suggested on OpenBSD that you reported.
>
>> OpenBSD 3.9-current/x86:
>>
>> without stats:
>> 0m6.79s real 0m1.56s user 0m1.12s system
>>
>> -HEAD + stats:
>> 0m10.44s real 0m2.26s user 0m1.22s system
>>
>> -HEAD + stats + patch:
>> 0m10.68s real 0m2.16s user 0m1.36s system
yep those are very stable even over a large number of runs
>
> and I got similar results reported from a Debian:
>
> Linux 2.6.16 on a single processor HT 2.8Ghz Pentium compiled
> with gcc 4.0.4.
>
> > > real 0m3.306s
> > > real 0m4.905s
> > > real 0m4.448s
>
> I am unclear on the cuase for the widely varying results you saw in
> Debian.
>
I can reproduce the widely varying results on a number of x86 and x86_64
based Linux boxes here (Debian,Fedora and CentOS) though I cannot
reproduce it on a Fedora core 5/ppc box.
All the x86 boxes are SMP - while the ppc one is not - that might have
some influence on the results.
Stefan
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To: pgsql-performance@postgresql.org
Cc: stefan@kaltenbrunner.cc, pgman@candle.pha.pa.us, zhouqq@cs.toronto.edu, pgsql-hackers@postgresql.org
Subject: Re: Test request for Stats collector performance improvement
In-Reply-To: <4492F517.7060405@kaltenbrunner.cc>
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