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To: Robert Haas <robertmhaas@gmail.com>
cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	Florian Helmberger <fh@25th-floor.com>,
	Alvaro Herrera <alvherre@commandprompt.com>,
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Subject: Re: [ADMIN] pg_class reltuples/relpages not updated by
	autovacuum/vacuum
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Fri, 27 May 2011 11:07:05 -0400"
Date: Fri, 27 May 2011 14:34:10 -0400
Message-ID: <17685.1306521250@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Robert Haas <robertmhaas@gmail.com> writes:
> Still, maybe we don't have a better option.  If it were me, I'd add an
> additional safety valve: use your formula if the percentage of the
> relation scanned is above some threshold where there's unlikely to be
> too much skew.  But if the percentage scanned is too small, then don't
> use that formula.  Instead, only update relpages/reltuples if the
> relation is now larger; set relpages to the new actual value, and
> scale up reltuples proportionately.

Ah, progress: now we're down to arguing about the size of the fudge
factor ;-).  I'll do something involving derating the reliability
when the number is coming from VACUUM.

			regards, tom lane