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Re: Problem with 8.4 stats collector high load

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Jakub Ouhrabka <jakub(dot)ouhrabka(at)comgate(dot)cz>
Cc: Jakub Ouhrabka <kuba(at)comgate(dot)cz>, Greg Smith <greg(at)2ndquadrant(dot)com>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Problem with 8.4 stats collector high load
Date: 2010-02-16 18:59:58
Message-ID: 20100216185958.GL5330@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Jakub Ouhrabka wrote:
> > Maybe you should decrease naptime a bit.
> 
> That did the trick, thanks!
> 
> > Yes.  There were some changes that needed to be done to autovacuum so
> > that it didn't read the stats file too often, but I don't recall if I
> > got around to it.
> 
> I looked at the strace output and there are *writes* to the file not
> reads. Why? Is it a consequence of this optimization?
> 
> Release notes 8.4:
> 
> Reduce I/O load of writing the statistics collection file by writing
> the file only when requested (Martin Pihlak)
> 
> Was autovacuum requesting to write this 20MB file 650x per minute?

Yes, exactly.

Ideally, autovacuum would only request a new copy of the file if the one
it got was considerably out of date.  Obviously a tenth of a second is
not old enough.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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