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. > ... ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org