Re: force the use of a particular index

От: Scott Cain
Тема: Re: force the use of a particular index
Дата: ,
Msg-id: 1057947784.5767.39.camel@localhost.localdomain
(см: обсуждение, исходный текст)
Ответ на: Re: force the use of a particular index  (Rod Taylor)
Список: pgsql-performance

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force the use of a particular index  (Scott Cain, )
 Re: force the use of a particular index  (Rod Taylor, )
  Re: force the use of a particular index  (Scott Cain, )
   Re: force the use of a particular index  (Rod Taylor, )
 Re: force the use of a particular index  (Rod Taylor, )
  Re: force the use of a particular index  (Scott Cain, )
 Re: force the use of a particular index  (Scott Cain, )
  Re: force the use of a particular index  (Rod Taylor, )
   Re: force the use of a particular index  (Scott Cain, )
 Re: force the use of a particular index  (Tom Lane, )
  Re: force the use of a particular index  (Scott Cain, )
   Re: force the use of a particular index  (Tom Lane, )

On Fri, 2003-07-11 at 14:14, Rod Taylor wrote:
> > > set enable_hashjoin = false;
> >
> > BINGO!
>
> I'm not so sure about that.  Your dataset seems to have changed fairly
> significantly since the last test.
>
> > ->  Index Scan using feature_pkey on feature f  (cost=0.00..134592.43 rows=47912 width=39) (actual
time=0.46..502.50rows=431 loops=1) 
>
> Notice it only pulled out 431 rows where prior runs pulled out several
> thousand (~13000).  I think what really happened was something came
> along and deleted a bunch of stuff, then vacuum ran.

There is nearly a zero chance that happened.  This database is
accessible only by me, I haven't deleted anything.  The only things I
have done is to create and drop various indexes and run vacuum.  Is
there anything else that could explain the difference?  Is the index
scan on feature_pkey using information from the index scan on
featureloc_src_6 to limit the number of rows to get from feature?

Scott

--
------------------------------------------------------------------------
Scott Cain, Ph. D.                                         
GMOD Coordinator (http://www.gmod.org/)                     216-392-3087
Cold Spring Harbor Laboratory



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