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Posted Tuesday, November 27, 2012 3:45 AM
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Hi all

When dealing with the Cost threshold for parallelism, I am almost certain that the Cost is not an amount in seconds but rather a number that SQL Server internally uses.

Is this correct?

I'm asking because I am going through a well-known book and it says: The "cost" is the estimated amount of time in seconds that it would take to execute

Is my understanding wrong?

Thanks
Post #1389057
Posted Tuesday, November 27, 2012 3:55 AM
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Hi,

I'm also of the understanding that "cost" is just an arbitrary no.

This link seems to back that up.

Thanks,

Simon




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Post #1389061
Posted Tuesday, November 27, 2012 3:56 AM


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From MSDN


The cost refers to an estimated elapsed time in seconds required to run the serial plan on a specific hardware configuration


http://msdn.microsoft.com/en-us/library/ms188603(v=SQL.105).aspx




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Post #1389064
Posted Tuesday, November 27, 2012 4:03 AM
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anthony.green (11/27/2012)
From MSDN


The cost refers to an estimated elapsed time in seconds required to run the serial plan on a specific hardware configuration


http://msdn.microsoft.com/en-us/library/ms188603(v=SQL.105).aspx


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Post #1389069
Posted Tuesday, November 27, 2012 4:08 AM


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I stand corrected.



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Post #1389070
Posted Tuesday, November 27, 2012 4:41 AM
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anthony.green (11/27/2012)
I stand corrected.


Can I assume that my documentation is incorrect then?
Post #1389087
Posted Tuesday, November 27, 2012 5:02 AM


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Yes I would as Gail has mentioned that the documentation on MSDN is incorrect, so anything which says its in seconds is incorrect.



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Post #1389107
Posted Tuesday, November 27, 2012 5:04 AM


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Yes I would as Gail has mentioned that the documentation on MSDN is incorrect, so anything which says its in seconds is incorrect.



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Post #1389108
Posted Tuesday, November 27, 2012 7:25 AM


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It's not seconds (anymore). It's a meaningless, unitless number.

It was originally based off of seconds on a specific benchmark machine back when the QO was initially developed, back sometime in the mid 90's



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Post #1389185
Posted Wednesday, November 28, 2012 8:04 AM


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Just remember that the number is an estimate. This means it can be wildly inaccurate. But, it's the only number you get, so you're going to use it, just don't rely on it.

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