On Tue, May 06, 2003 at 12:25:33AM -0400, Tom Lane wrote:
> Josh Berkus <josh@agliodbs.com> writes:
> > THE IDEA: The planner should keep statistics on the correlation of foreign
> > keys and apply them to the expected row counts for EXISTS clause limitations,
> > and possibly for other query types as well.
>
> It's a thought. Keeping complete cross-column correlation stats (for
> every combination of columns in the DB) is obviously out of the
> question. If you're gonna do it you need a heuristic to tell you which
> combinations of columns are worth keeping track of --- and foreign-key
> relationships seem like a reasonable guide to the interesting
> combinations.
What if the optimizer kept on-going statistics on what columns were used
in joins to what other columns? Over time this would allow analyze to
determine on it's own what cross-column correlation stats should be
kept.
--
Jim C. Nasby (aka Decibel!) jim@nasby.net
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