Re: Are statistics gathered on function indexes?

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От Tom Lane
Тема Re: Are statistics gathered on function indexes?
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Msg-id 9389.1025296584@sss.pgh.pa.us
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Ответ на Re: Are statistics gathered on function indexes?  (Ray Ontko <rayo@ontko.com>)
Ответы Re: Are statistics gathered on function indexes?  (Ray Ontko <rayo@ontko.com>)
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Ray Ontko <rayo@ontko.com> writes:
> 1) here's the "bad" stats.
> 2) here's the "good" stats.
> Note that the information really is different.

Yeah.  It seems that the critical difference is the null_frac; if I take
your "bad" values and change null_frac to 0 then I get
reasonable-looking answers, but with null_frac = 0.000333333 I indeed
get bad answers.  I suspect null_frac is getting double-counted
somewhere, and depending on just how many nulls ANALYZE happens to find,
you might get pushed over the edge from a small selectivity to zero or
negative selectivity.  Will dig further.

            regards, tom lane



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