Re: index / sequential scan problem

От: Paul Thomas
Тема: Re: index / sequential scan problem
Дата: ,
Msg-id: 20030717111248.C27264@bacon
(см: обсуждение, исходный текст)
Ответ на: index / sequential scan problem  (Fabian Kreitner)
Ответы: Re: index / sequential scan problem  (Fabian Kreitner)
Список: pgsql-performance

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index / sequential scan problem  (Fabian Kreitner, )
 Re: index / sequential scan problem  ("Shridhar Daithankar", )
  Re: index / sequential scan problem  (Fabian Kreitner, )
   Re: index / sequential scan problem  ("Shridhar Daithankar", )
 Re: index / sequential scan problem  (Paul Thomas, )
  Re: index / sequential scan problem  (Fabian Kreitner, )
   Re: index / sequential scan problem  (Paul Thomas, )
    Re: index / sequential scan problem  (Fabian Kreitner, )
     Re: index / sequential scan problem  ("Shridhar Daithankar", )
     Re: index / sequential scan problem  (Jord Tanner, )
     Re: index / sequential scan problem  (Paul Thomas, )
      Re: index / sequential scan problem  (Tom Lane, )
   Re: index / sequential scan problem  (Tom Lane, )
    Re: index / sequential scan problem  (Fabian Kreitner, )
     Re: index / sequential scan problem  (Fabian Kreitner, )
      Re: index / sequential scan problem  (Dennis Björklund, )
       Re: index / sequential scan problem  (Tom Lane, )
        Re: index / sequential scan problem  ("scott.marlowe", )
        Re: index / sequential scan problem  (Dennis Björklund, )

On 17/07/2003 10:01 Fabian Kreitner wrote:

Hi Fabian,

When you are doing these kinds of tests, you need to be aware that the
kernel may have most of your data cached after the first query and this
may be why the second query appears to run faster.

Also don't be worried if the planner chooses a seq scan for small tables
as the whole table can often be bought into memory with one IO whereas
reading the index then the table would be 2 IOs.
HTH

--
Paul Thomas
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