On Mon, Aug 9, 2021 at 09:20:53AM -0700, David G. Johnston wrote: > On Mon, Aug 9, 2021 at 9:06 AM David G. Johnston <david.g.johns...@gmail.com> > wrote: > > On Mon, Aug 9, 2021 at 8:02 AM PG Doc comments form > <nore...@postgresql.org > > wrote: > > Hello, on page > https://www.postgresql.org/docs/current/row-estimation-examples.html - > there > is a example: > selectivity = (1 - null_frac1) * (1 - null_frac2) * min(1/ > num_distinct1, > 1/num_distinct2) > = (1 - 0) * (1 - 0) / max(10000, 10000) > = 0.0001 > in the first string " * min" and in the second " / max" > as I understand it isn't correct. > > > Division is just multiplication by the reciprocal so while the > presentation > here is inconsistent it is correct. Likewise, the larger a number the > smaller its reciprocal, so the change from min to max also works. > > > > FWIW this used to be presented with the calculation and formula in sync, but > the original had a simple typo in the calculation. When the typo got fixed > back in December of 2007 [1] the author of the patch simplified the > calculation > at the same time. I suggest we update the formula line to match the > calculation presented.
Nice, can you provide a patch please? -- Bruce Momjian <br...@momjian.us> https://momjian.us EDB https://enterprisedb.com If only the physical world exists, free will is an illusion.
