Re: poor performance when recreating constraints on large tables

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От Kevin Grittner
Тема Re: poor performance when recreating constraints on large tables
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Msg-id 4DEF8CEC020000250003E38D@gw.wicourts.gov
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Ответ на Re: poor performance when recreating constraints on large tables  (Samuel Gendler <sgendler@ideasculptor.com>)
Ответы Re: poor performance when recreating constraints on large tables  (Samuel Gendler <sgendler@ideasculptor.com>)
Список pgsql-performance
Samuel Gendler <sgendler@ideasculptor.com> wrote:

> The planner knows how many rows are expected for each step of the
> query plan, so it would be theoretically possible to compute how
> far along it is in processing a query based on those estimates,
> wouldn't it?

And it is sometimes off by orders of magnitude.  How much remaining
time do you report when the number of rows actually processed so far
is five times the estimated rows that the step would process?  How
about after it chugs on from there to 20 time she estimated row
count?  Of course, on your next query it might finish after
processing only 5% of the estimated rows....

-Kevin

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