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To: Robert Haas <robertmhaas@gmail.com>
cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>,
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	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 "Thu, 26 May 2011 15:48:29 -0400"
Date: Thu, 26 May 2011 16:30:09 -0400
Message-ID: <28829.1306441809@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Robert Haas <robertmhaas@gmail.com> writes:
> Except that's not how it works.  At least in the case of ANALYZE, we
> *aren't* counting all the tuples in the table.  We're selecting a
> random sample of pages and inferring a tuple density, which we then
> extrapolate to the whole table and store.  Then when we pull it back
> out of the table, we convert it back to a tuple density.  The real
> value we are computing and using almost everywhere is tuple density;
> storing a total number of tuples in the table appears to be just
> confusing the issue.

If we were starting in a green field we might choose to store tuple
density.  However, the argument for changing it now is at best mighty
thin; IMO it is not worth the risk of breaking client code.

			regards, tom lane