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Re: [HACKERS] EXPLAIN ANALYZE on 8.2

From: Florian Weimer <fweimer(at)bfk(dot)de>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: "Martijn van Oosterhout" <kleptog(at)svana(dot)org>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Kelly Burkhart" <kelly(dot)burkhart(at)gmail(dot)com>, "Evgeny Gridasov" <eugrid(at)fpm(dot)kubsu(dot)ru>, <pgsql-performance(at)postgresql(dot)org>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] EXPLAIN ANALYZE on 8.2
Date: 2006-12-15 12:32:20
Message-ID: 82irgdnxuz.fsf@mid.bfk.de (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
* Simon Riggs:

>> I think the best option is setitimer(), but it's not POSIX so
>> platform support is going to be patchy.
>
> Don't understand that. I thought that was to do with alarms and
> signals.

You could use it for sampling.  Every few milliseconds, you record
which code is executing (possibly using a global variable which is set
and reset accordingly).  But this might lead to tons of interrupted
system calls, and not all systems mask them, so this might not be an
option for the PostgreSQL code base.

On the other hand, if performance in more recent Linux releases (from
kernel.org) are acceptable, you should assume that the problem will
eventually fix itself.  FWIW, I see the 9x overhead on something that
is close to 2.6.17 (on AMD64/Opteron), so this could be wishful
thinking. 8-(

-- 
Florian Weimer                <fweimer(at)bfk(dot)de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstra├če 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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