Re: BUG #13348: PostgreSQL 9.5 sampletable BUG return rows not the same as reltuples*sample factor?

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От Tom Lane
Тема Re: BUG #13348: PostgreSQL 9.5 sampletable BUG return rows not the same as reltuples*sample factor?
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Msg-id 10017.1432570191@sss.pgh.pa.us
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Ответ на BUG #13348: PostgreSQL 9.5 sampletable BUG return rows not the same as reltuples*sample factor?  (digoal@126.com)
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digoal@126.com writes:
> But when use BERNOULLI sample method, it's return rows not the same as
> reltuples*factor.
> Can we add filter to exact return rows equal to reltuples*factor ?

No.  It is neither practical nor required by the standard that the number
of returned rows be exactly N*S.  If we tried to do that, rows near the
end of the table would end up having a different probability of being
selected than rows near the front.

            regards, tom lane

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