Date: Tue, 11 Jul 2006 09:59:51 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Katsuhiko Okano <okano.katsuhiko@oss.ntt.co.jp>
Cc: pgsql-hackers@postgresql.org
Subject: Re: poor performance with Context Switch Storm at TPC-W.
Message-ID: <20060711135951.GA3995@surnet.cl>
Mail-Followup-To: Katsuhiko Okano <okano.katsuhiko@oss.ntt.co.jp>,
	pgsql-hackers@postgresql.org
References: <200607112009.FED09315.TLPPUBIBOPuVLJL@oss.ntt.co.jp>
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Katsuhiko Okano wrote:

> I suspected conflict of BufMappingLock.
> but, collected results are seen,
> occurrence of CSStorm and the increase of BufMappingLock counts
> seem not to correspond.
> Instead, SubtransControlLock and SubTrans were increasing.
> I do not understand what in the cause of CSStorm.

Please see this thread:
http://archives.postgresql.org/pgsql-hackers/2005-11/msg01547.php
(actually it's a single message AFAICT)

This was applied on the 8.2dev code, so I'm surprised that 8.2dev
behaves the same as 8.1.

Does your problem have any relationship to what's described there?

I also wondered whether the problem may be that the number of SLRU
buffers we use for subtrans is too low.  But the number was increased
from the default 8 to 32 in 8.2dev as well.  Maybe you could try
increasing that even further; say 128 and see if the problem is still
there.  (src/include/access/subtrans.h, NUM_SUBTRANS_BUFFERS).

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.