Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Nathan Boley" <npboley(at)gmail(dot)com>
Cc: "Jeff Davis" <pgsql(at)j-davis(dot)com>, "Zeugswetter Andreas OSB sIT" <Andreas(dot)Zeugswetter(at)s-itsolutions(dot)at>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics
Date: 2008-06-12 18:07:31
Message-ID: 12033.1213294051@sss.pgh.pa.us
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"Nathan Boley" <npboley(at)gmail(dot)com> writes:
> Given that, wouldn't it be smarter to consider a value as an mcv
> candidate iff it has a density greater than 0.005, rather than having
> a count greater than 1.5*average?

Yeah, perhaps ... want to experiment with that? Though I'd be a bit
worried about how to get the threshold right, seeing that it will
depend a whole lot on what the user has selected for random_page_cost
and other parameters.

regards, tom lane

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