Re: Postgres 9.0 has a bias against indexes

От: Kevin Grittner
Тема: Re: Postgres 9.0 has a bias against indexes
Дата: ,
Msg-id: 4D4192A10200002500039EEA@gw.wicourts.gov
(см: обсуждение, исходный текст)
Ответ на: Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala)
Список: pgsql-performance

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Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
 Re: Postgres 9.0 has a bias against indexes  (Kenneth Marshall, )
  Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
   Re: Postgres 9.0 has a bias against indexes  (David Wilson, )
    Re: Postgres 9.0 has a bias against indexes  (Tom Lane, )
     Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
      Re: Postgres 9.0 has a bias against indexes  ("Igor Neyman", )
       Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
        Re: Postgres 9.0 has a bias against indexes  (Scott Marlowe, )
         Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
          Re: Postgres 9.0 has a bias against indexes  (Scott Marlowe, )
           Re: Postgres 9.0 has a bias against indexes  ("Igor Neyman", )
            Re: Postgres 9.0 has a bias against indexes  (Scott Marlowe, )
             Re: Postgres 9.0 has a bias against indexes  ("Igor Neyman", )
              Re: Postgres 9.0 has a bias against indexes  (Scott Marlowe, )
               Re: Postgres 9.0 has a bias against indexes  ("Igor Neyman", )
                Re: Postgres 9.0 has a bias against indexes  (Scott Marlowe, )
               Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
            Re: Postgres 9.0 has a bias against indexes  (Kenneth Marshall, )
             Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )
              Re: Postgres 9.0 has a bias against indexes  ("Kevin Grittner", )
 Re: Postgres 9.0 has a bias against indexes  ("Kevin Grittner", )
 Re: Postgres 9.0 has a bias against indexes  (J Sisson, )
  Re: Postgres 9.0 has a bias against indexes  (Mladen Gogala, )

Mladen Gogala <> wrote:

> Yes,  Oracle can be forced into doing a sequential scan and it is
> actually faster than an index scan:

And PostgreSQL can be coerced to use an indexed scan.  Its plans are
cost-based, with user configurable cost factors; so if you tell it
that seq_page_cost and random_page_cost are both equal to some
really low value (like 0.001), you'll get an index scan.  Part of
the process of tuning PostgreSQL is to discover the relative
*actual* costs on *your environment* (which is largely dependent on
the degree of caching of the active portion of your database).  When
you get your costing factors to approximate reality, the optimizer
will do a pretty good job of picking the fastest plan.

-Kevin


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