Re: Forcing the use of particular execution plans

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От Jim C. Nasby
Тема Re: Forcing the use of particular execution plans
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Msg-id 20060927201350.GS19827@nasby.net
обсуждение исходный текст
Ответ на Re: Forcing the use of particular execution plans  ("Dave Dutcher" <dave@tridecap.com>)
Ответы Re: Forcing the use of particular execution plans  (Ron Mayer <rm_pg@cheapcomplexdevices.com>)
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On Wed, Sep 27, 2006 at 10:51:26AM -0500, Dave Dutcher wrote:
> To make the planner prefer an index scan over a seq scan, I would first
> check the statistics again, and then you can try setting enable_seqscan to
> false (enable_seqscan is meant more for testing than production) or, you
> could try reducing random_page_cost, but you should test that against a
> range of queries before putting it in production.

Index scans are also pretty picky about correlation. If you have really
low correlation you don't want to index scan, but I think our current
estimates make it too eager to switch to a seqscan.
--
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)

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