Re: Hash Join cost estimates - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Hash Join cost estimates
Date
Msg-id 2942.1364589445@sss.pgh.pa.us
Whole thread Raw
In response to Re: Hash Join cost estimates  (Jeff Davis <pgsql@j-davis.com>)
Responses Re: Hash Join cost estimates  (Jeff Davis <pgsql@j-davis.com>)
Re: Hash Join cost estimates  (Stephen Frost <sfrost@snowman.net>)
List pgsql-hackers
Jeff Davis <pgsql@j-davis.com> writes:
> Yes, I have run into this issue (or something very similar). I don't
> understand why the bucketsize even matters much -- assuming few hash
> collisions, we are not actually evaluating the quals any more times than
> necessary. So why all of the hashjoin-specific logic in determining the
> number of qual evaluations? The only reason I can think of is to model
> the cost of comparing the hashes themselves.

I think the point is that there may *not* be few hash collisions ...
        regards, tom lane



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