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Re: Huge number of disk writes after migration to 8.1

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgreSQL(dot)org
Subject: Re: Huge number of disk writes after migration to 8.1
Date: 2006-01-18 19:24:00
Message-ID: 20060118192359.GH19933@surnet.cl (view raw or flat)
Thread:
Lists: pgsql-bugspgsql-patches
Tom Lane wrote:
> Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> > Well, if you issue a manual vacuum then you can argue that it has been
> > "modified" (it's seeing some activity).  But immediately after a vacuum
> > the table will not be vacuumed by autovac if there's no other activity,
> > because there's no need for it, so we can create the entry anyway and it
> > won't make an immediate difference.
> 
> You're ignoring the point of this thread, which is that creating
> hashtable entries for tables that aren't actively being modified
> causes significant ongoing overhead that we ought to try to minimize.

True.  I agree with the rest of the reasoning in this case.

Maybe the fact that the stat file is completely rewritten every 500 ms
should be reconsidered, if in the future someone chooses to rewrite
the stat system.  We can reconsider this part then, as well.

-- 
Alvaro Herrera                                http://www.PlanetPostgreSQL.org
Jason Tesser: You might not have understood me or I am not understanding you.
Paul Thomas: It feels like we're 2 people divided by a common language...

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