Re: More thoughts about planner's cost estimates

Josh, Greg, and Tom,

I do not know how sensitive the plans will be to the correlation,
but one thought might be to map the histogram X histogram correlation
to a square grid of values. Then you can map them to an integer which
would give you 8 x 8 with binary values, a 5 x 5 with 4 values per
point, or a 4 x 4 with 8 values per point. If close is good enough,
that would be a compact way to store some histogram cross correlation
information.

Ken

On Thu, Jun 01, 2006 at 01:50:26PM -0700, Josh Berkus wrote:
> Greg, Tom,
>
> ...
> > 2) It isn't even clear what data you're exactly looking for. Certainly
> > "correlation" is just shorthand here and isn't what you're actually
> > looking for.
>
> Actually, I'd think that a correlation number estimate (0 = complete
> uncorrelated, 1 = completely correlated) would be sufficient to improve
> row count estimation significantly, without incurring the vast overhead of
> histogramXhistorgram manipulation.
> ...