Re: Questions on query planner, join types, and work_mem

От: Hannu Krosing
Тема: Re: Questions on query planner, join types, and work_mem
Дата: ,
Msg-id: 1280944268.3735.12.camel@hvost
(см: обсуждение, исходный текст)
Ответ на: Re: Questions on query planner, join types, and work_mem  (Robert Haas)
Ответы: Re: Questions on query planner, join types, and work_mem  (Tom Lane)
Список: pgsql-performance

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Questions on query planner, join types, and work_mem  (Peter Hussey, )
 Re: Questions on query planner, join types, and work_mem  (Andres Freund, )
 Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
  Re: Questions on query planner, join types, and work_mem  (Alvaro Herrera, )
   Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
 Re: Questions on query planner, join types, and work_mem  (Jayadevan M, )
 Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
  Re: Questions on query planner, join types, and work_mem  (Peter Hussey, )
   Re: Questions on query planner, join types, and work_mem  (Robert Haas, )
   Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
   Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
    Re: Questions on query planner, join types, and work_mem  (Robert Haas, )
     Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
      Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
       Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
        Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
         Re: Questions on query planner, join types, and work_mem  (Greg Smith, )
          Re: Questions on query planner, join types, and work_mem  (Greg Smith, )
          Re: Questions on query planner, join types, and work_mem  ("Kevin Grittner", )
           Re: Questions on query planner, join types, and work_mem  (Greg Smith, )
            Re: Questions on query planner, join types, and work_mem  ("Kevin Grittner", )
          Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
         Re: Questions on query planner, join types, and work_mem  (Tom Lane, )
         Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
          Re: Questions on query planner, join types, and work_mem  ("Kevin Grittner", )
         Re: Questions on query planner, join types, and work_mem  (Hannu Krosing, )
       Re: Questions on query planner, join types, and work_mem  (Bruce Momjian, )
        Re: Questions on query planner, join types, and work_mem  (Robert Haas, )
         Re: Questions on query planner, join types, and work_mem  (Bruce Momjian, )
          Re: Questions on query planner, join types, and work_mem  (Bruce Momjian, )
   Re: Questions on query planner, join types, and work_mem  ("Kevin Grittner", )
 Re: Questions on query planner, join types, and work_mem  (Greg Smith, )

On Wed, 2010-08-04 at 09:14 -0400, Robert Haas wrote:
> On Tue, Aug 3, 2010 at 3:03 AM, Hannu Krosing <> wrote:
> > In case of fully cached database it is closer to 1.
>
> In the case of a fully cached database I believe the correct answer
> begins with a decimal point.

The number 1 here was suggested in relation to seq_page_cost, which is
1.

For fully cached db there is no additional seek time for random access,
so seq_page_cost == random_page_cost.

Of course there are more variables than just *_page_cost, so if you nail
down any other one, you may end with less than 1 for both page costs.

I have always used seq_page_cost = 1 in my thinking and adjusted others
relative to it.

--
Hannu Krosing   http://www.2ndQuadrant.com
PostgreSQL Scalability and Availability
   Services, Consulting and Training




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