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

On Wed, 2010-08-04 at 09:14 -0400, Robert Haas wrote:
> On Tue, Aug 3, 2010 at 3:03 AM, Hannu Krosing <hannu@2ndquadrant.com> 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
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