Re: 7.4 vs 7.3 ( hash join issue )

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От Greg Stark
Тема Re: 7.4 vs 7.3 ( hash join issue )
Дата
Msg-id 87y8j2ctc3.fsf@stark.xeocode.com
обсуждение исходный текст
Ответ на Re: 7.4 vs 7.3 ( hash join issue )  (Gaetano Mendola <mendola@bigfoot.com>)
Ответы Re: 7.4 vs 7.3 ( hash join issue )  (Dennis Bjorklund <db@zigo.dhs.org>)
Список pgsql-performance
Gaetano Mendola <mendola@bigfoot.com> writes:

> hash_join = on
>                 ->  Seq Scan on lookup_tipo_evento le  (cost=0.00..1.16 rows=16 width=32) (actual time=0.017..0.038
rows=16loops=1) 
>
> hash_join = off
>                       ->  Seq Scan on lookup_tipo_evento le  (cost=0.00..1.16 rows=16 width=32) (never executed)


Actually this looks like it's arguably a bug to me. Why does the hash join
execute the sequential scan at all? Shouldn't it also like the merge join
recognize that the other hashed relation is empty and skip the sequential scan
entirely?


--
greg

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