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Thread Query Plan Cost value: We should take this at face value, yes?
Wed, Nov 8 2006 8:52 PMPermanent Link

Sam Jones
Hello!

Doing some testing using DBISAM 4.24

I read in a thread:
http://www.elevatesoft.com/scripts/newsgrp.dll?action=openmsg&group=5&msg=45045&page=1#msg45045

That the 'cost' value seen in a query plan is "for real."

IOW, if I have two queries, and one has a cost of 40kb, and the other (which returns the
same data) has a cost of 460kb, I really really want to use the 40kb flavor, right?

(this is a tame query, returning 177 rows from a 3000 row table).

Thank you!
Thu, Nov 9 2006 3:41 PMPermanent Link

Tim Young [Elevate Software]

Elevate Software, Inc.

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Email timyoung@elevatesoft.com

Sam,

<< That the 'cost' value seen in a query plan is "for real." >>

As real as can be expected.  The index scan costs have to be adjusted a bit
to account for index page slack space, but other than that they are exact.

<< IOW, if I have two queries, and one has a cost of 40kb, and the other
(which returns thesame data) has a cost of 460kb, I really really want to
use the 40kb flavor, right? >>

Correct.

--
Tim Young
Elevate Software
www.elevatesoft.com

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