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Query Plan Cost value: We should take this at face value, yes? |
Wed, Nov 8 2006 8:52 PM | Permanent 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 PM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. 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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