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

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Nathan Boley <npboley(at)gmail(dot)com>
Cc: Zeugswetter Andreas OSB sIT <Andreas(dot)Zeugswetter(at)s-itsolutions(dot)at>, Gregory Stark <stark(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics
Date: 2008-06-10 18:32:40
Message-ID: 1213122760.24243.48.camel@dogma.ljc.laika.com
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On Tue, 2008-06-10 at 08:51 -0700, Nathan Boley wrote:
> >> > One more problem with low ndistinct values is that the condition might very well
> >> > hit no rows at all. But Idea 1 will largely overestimate the number of hits.
>
> Thats a good point, but I don't see a clear solution. Maybe we could

I think that MCVs are the solution, right? A low ndistinct means that
those values will likely be MCVs.

Since you brought up a different process for choosing MCVs, maybe a
better name might be "Most Interesting Values".

Regards,
Jeff Davis

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