Re: same query different execution plan (hash join vs. semi-hash join) - Mailing list pgsql-performance

From Tom Lane
Subject Re: same query different execution plan (hash join vs. semi-hash join)
Date
Msg-id 868.1400509337@sss.pgh.pa.us
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In response to Re: same query different execution plan (hash join vs. semi-hash join)  ("Huang, Suya" <Suya.Huang@au.experian.com>)
Responses Re: same query different execution plan (hash join vs. semi-hash join)  ("Huang, Suya" <Suya.Huang@au.experian.com>)
List pgsql-performance
"Huang, Suya" <Suya.Huang@au.experian.com> writes:
> Thank you Tom. But the time spent on scanning table test1 is less than 1 second (91.738 compares to 87.869), so I
guessthis shouldn't be the issue? 

No, the point is that the bad rowcount estimate (and, possibly, lack of
stats about join column contents) causes the planner to pick a join method
that's not ideal for this query.

            regards, tom lane


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