I think the thread you're thinking of is on or about this post:
http://archives.postgresql.org/pgsql-patches/2003-12/msg00039.php
Manfred Koizar produced a patch that modified index correlation by
sorting equal key values based on item pointers. The patch went as far
as getting accepted into the patch queue, but Tom raised some doubts
about it and it was subsequently removed.
Robert Treat
On Mon, 2004-03-08 at 14:41, Josh Berkus wrote:
> Tom,
>
> > Are you sure you're not thinking of stats for functional indexes?
>
> Positive. I even remember seeing that the patch was accepted.
>
> The patch specifically had to do with a multi-column correlation algorithm for
> improving the selectivity of multi-column indexes.
>
> Problem is, with 1400 posts per month August to October, I can't find it, and
> the keywords that I think are obvious don't turn anything up.
>
> --
> -Josh Berkus
> Aglio Database Solutions
> San Francisco
>
>
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