Query Cost - how is it calculated?

Hi,
I'm trying to figure out where the value of "Cost" comes from in the
Query Analyzer.
For example, when running this on Northwind:
select * from dbo.[Alphabetical list of products]
You get this 3 parts for the Query Plan. The part of
"Categories.PK_Categories" has a cost of 24% of the
total and a value of 0.0119... Where does this value
come from?
All I get is "cost for CPU" and "cost for I/O" - but adding
these together does not equal that value.
Anyone have a clue?
With regards,
Martijn Tonies
Database Workbench - tool for InterBase, Firebird, MySQL, Oracle & MS SQL
Server
Upscene Productions
http://www.upscene.comI doubt that anyone outside of Microsft, and maybe Kalen, could really
answer that question...
Not only does the optimizer estimate IO and CPU, it does some estimation
about how much physical IO is required based on some expectation of how much
of the data might be in memory... It also looks at the recent use of tables
to determine the level of locking for certain operations as well...
Wayne Snyder, MCDBA, SQL Server MVP
Mariner, Charlotte, NC
www.mariner-usa.com
(Please respond only to the newsgroups.)
I support the Professional Association of SQL Server (PASS) and it's
community of SQL Server professionals.
www.sqlpass.org
"Martijn Tonies" <m.tonies@.upscene-removethis.nospam.com> wrote in message
news:ekzghVpZFHA.3040@.TK2MSFTNGP14.phx.gbl...
> Hi,
> I'm trying to figure out where the value of "Cost" comes from in the
> Query Analyzer.
> For example, when running this on Northwind:
> select * from dbo.[Alphabetical list of products]
> You get this 3 parts for the Query Plan. The part of
> "Categories.PK_Categories" has a cost of 24% of the
> total and a value of 0.0119... Where does this value
> come from?
> All I get is "cost for CPU" and "cost for I/O" - but adding
> these together does not equal that value.
>
> Anyone have a clue?
> --
> With regards,
> Martijn Tonies
> Database Workbench - tool for InterBase, Firebird, MySQL, Oracle & MS SQL
> Server
> Upscene Productions
> http://www.upscene.com
>
>|||Hello Wayne,

> I doubt that anyone outside of Microsft, and maybe Kalen, could really
> answer that question...
> Not only does the optimizer estimate IO and CPU, it does some estimation
> about how much physical IO is required based on some expectation of how
much
> of the data might be in memory... It also looks at the recent use of
tables
> to determine the level of locking for certain operations as well...
Hmm - when extracting a plan via SHOWPLAN_ALL, I do get the estimates
of some of the info (IO/CPU), but I have no idea where the actual "cost"
comes
from.
I've been fiddling around with multiplying IO * "nr of executes" and CPU *
nr of
executes, but it doesn't really add up properly... :-/
With regards,
Martijn Tonies
Database Workbench - tool for InterBase, Firebird, MySQL, Oracle & MS SQL
Server
Upscene Productions
http://www.upscene.com

>
> --
> Wayne Snyder, MCDBA, SQL Server MVP
> Mariner, Charlotte, NC
> www.mariner-usa.com
> (Please respond only to the newsgroups.)
> I support the Professional Association of SQL Server (PASS) and it's
> community of SQL Server professionals.
> www.sqlpass.org
> "Martijn Tonies" <m.tonies@.upscene-removethis.nospam.com> wrote in message
> news:ekzghVpZFHA.3040@.TK2MSFTNGP14.phx.gbl...
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