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List:       pgsql-performance
Subject:    Re: [PERFORM] Postgres 9.0 has a bias against indexes
From:       "Kevin Grittner" <Kevin.Grittner () wicourts ! gov>
Date:       2011-01-27 21:43:29
Message-ID: 4D4192A10200002500039EEA () gw ! wicourts ! gov
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Mladen Gogala <mladen.gogala@vmsinfo.com> 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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