| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | ivanmulhin(at)gmail(dot)com, Pg Docs <pgsql-docs(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: incorrect information in documentation |
| Date: | 2021-08-09 16:06:16 |
| Message-ID: | CAKFQuwbHsQ14v3i4oEwPOmgEBqEFjG4i=WsuOMmP2q82myvdQQ@mail.gmail.com |
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| Lists: | pgsql-docs |
On Mon, Aug 9, 2021 at 8:02 AM PG Doc comments form <noreply(at)postgresql(dot)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.
David J.
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