Re: Query about index usage

От: Kevin Grittner
Тема: Re: Query about index usage
Дата: ,
Msg-id: 4C120F0B02000025000321BE@gw.wicourts.gov
(см: обсуждение, исходный текст)
Ответ на: Query about index usage  (Jayadevan M)
Ответы: Re: Query about index usage  (Jayadevan M)
Список: pgsql-performance

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Re: Analysis Function  (David Jarvis, )
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      Re: Query about index usage  ("Kevin Grittner", )
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           Re: Analysis Function  (David Jarvis, )
           Re: Analysis Function  (Tom Lane, )
            Re: Analysis Function  (Magnus Hagander, )
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               Re: Analysis Function  (Bruce Momjian, )
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 Re: Query about index usage  (Jayadevan M, )
  Re: Query about index usage  (Greg Smith, )
   Re: Query about index usage  (Jayadevan M, )

Jayadevan M <> wrote:

> One query about PostgreSQL's index usage. If I select just one
> column on which there is an index (or select only columns on which
> there is an index), and the index is used by PostgreSQL, does
> PostgreSQL avoid table access if possible?

PostgreSQL can't currently avoid reading the table, because that's
where the tuple visibility information is stored.  We've been making
progress toward having some way to avoid reading the table for all
except very recently written tuples, but we're not there yet (in any
production version or in the 9.0 version to be released this
summer).

-Kevin


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