To: pgsql-hackers@postgresql.org
Subject: CSStorm occurred again by postgreSQL8.2. (Re: poor performance with
	Context Switch Storm at TPC-W.)
From: Katsuhiko Okano <okano.katsuhiko@oss.ntt.co.jp>
References: <200607112009.FED09315.TLPPUBIBOPuVLJL@oss.ntt.co.jp>
	<20060711135951.GA3995@surnet.cl>
	<200607141457.CFC04165.PBLJLPVTILUBOPu@oss.ntt.co.jp>
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Message-Id: <200607181650.EDC81237.LOBJUTPuIPPBLLV@oss.ntt.co.jp>
Date: Tue, 18 Jul 2006 16:50:43 +0900
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Katsuhiko Okano wrote:
> By PostgreSQL8.2, NUM_SUBTRANS_BUFFERS was changed into 128
> and recompile and measured again.
> NOT occurrence of CSStorm. The value of WIPS was about 400.

measured again.
not occurrence when measured for 30 minutes.
but occurrence when measured for 3 hours, and 1 hour and 10 minutes passed.
It does not solve, even if it increases the number of NUM_SUBTRANS_BUFFERS.
The problem was only postponed.


> If the number of SLRU buffers is too low,
> also in PostgreSQL8.1.4, if the number of buffers is increased
> I think that the same result is brought.
> (Although the buffer of CLOG or a multi-transaction also increases,
> I think that effect is small)  
> 
> Now, NUM_SLRU_BUFFERS is changed into 128 in PostgreSQL8.1.4
> and is under measurement.

Occurrence CSStorm when the version 8.1.4 passed similarly for 
1 hour and 10 minutes.


A strange point,
The number of times of a LWLock lock for LRU buffers is 0 times
until CSStorm occurs.
After CSStorm occurs, the share lock and the exclusion lock are required and 
most locks are kept waiting.
(exclusion lock for SubtransControlLock is increased rapidly after CSStorm start.)


Is different processing done by whether CSStrom has occurred or not occurred?


regards,
--------
Katsuhiko Okano
okano katsuhiko _at_ oss ntt co jp