Re: Correlation in cost_index()

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Manfred Koizar <mkoi-pg(at)aon(dot)at>
Cc: "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Correlation in cost_index()
Date: 2002-10-03 18:50:00
Message-ID: 11083.1033671000@sss.pgh.pa.us
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Manfred Koizar <mkoi-pg(at)aon(dot)at> writes:
> Never mind! I just stumbled over those lines in selfuncs.c where
> indexCorrelation is calculated by dividing the correlation of the
> first index column by the number of index columns.

Yeah, I concluded later that that was bogus. I've been thinking of
just using the correlation of the first index column and ignoring
the rest; that would not be great, but it's probably better than what's
there. Have you got a better formula?

regards, tom lane

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