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.johnston@gmail.com>
> wrote:
>
> On Mon, Aug 9, 2021 at 8:02 AM PG Doc comments form <noreply@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 <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
If only the physical world exists, free will is an illusion.
