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help / color / mirror / Atom feedFrom: David G. Johnston <[email protected]>
To: [email protected]
To: Pg Docs <[email protected]>
Subject: Re: incorrect information in documentation
Date: Mon, 9 Aug 2021 09:06:16 -0700
Message-ID: <CAKFQuwbHsQ14v3i4oEwPOmgEBqEFjG4i=WsuOMmP2q82myvdQQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
On Mon, Aug 9, 2021 at 8:02 AM PG Doc comments form <[email protected]>
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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Subject: Re: incorrect information in documentation
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