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Understanding Graphical Execution Plans - Part 3: Analyzing the Plan


Understanding Graphical Execution Plans - Part 3: Analyzing the Plan

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darrenwhite
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Comments posted to this topic are about the item Understanding Graphical Execution Plans - Part 3: Analyzing the Plan
OldCursor
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This is the first time I have ever seen practical and really meaningful advise about the "black art" of query optimization. The timing is perfect because I need to do a lot of it at the moment.

Thanks for a very informative and helpful series of articles!

:-)
darrenwhite
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"This is the first time I have ever seen practical and really meaningful advise about the "black art" of query optimization. The timing is perfect because I need to do a lot of it at the moment.

Thanks for a very informative and helpful series of articles!"


I appreciate your feedback I am glad you found it helpful. If you would like more depth on the subject, I would recommend Grant Fritchey's book.
Grant Fritchey
Grant Fritchey
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Nice article.

A couple of notes. You state that the plan is read from right to left. That's not completely true. The logical processing order of the plan is from left to right, like reading a book. The data flow is from right to left. Frequently you're going to follow the data flow, but there are some plans, especially ones involving temporary storage in spools, that can only be appropriately understood by reading them left to right. That was a mistake in my first book that I fixed in the second edition.

You state that operator costs are estimates, good. But then you go on to implicate that they have direct correlation to performance and that's just not true. They're internal measuring sticks of meaning only to the optimizer and don't relate to the real world in any significant way. I'd be as clear as possible there. That's another thing I didn't make sufficiently clear in the first edition of my book.

Decent summary of how to read execution plans. Well done.

----------------------------------------------------
The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

The Scary DBA
Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
Grant Fritchey
Grant Fritchey
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OldCursor (2/25/2014)
This is the first time I have ever seen practical and really meaningful advise about the "black art" of query optimization. The timing is perfect because I need to do a lot of it at the moment.

Thanks for a very informative and helpful series of articles!

:-)


For more, follow the links in my signature below. The Execution Plans book is free as a download from here if you don't want a paper copy.

----------------------------------------------------
The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

The Scary DBA
Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
darrenwhite
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"Nice article.

A couple of notes. You state that the plan is read from right to left. That's not completely true. The logical processing order of the plan is from left to right, like reading a book. The data flow is from right to left. Frequently you're going to follow the data flow, but there are some plans, especially ones involving temporary storage in spools, that can only be appropriately understood by reading them left to right. That was a mistake in my first book that I fixed in the second edition.

You state that operator costs are estimates, good. But then you go on to implicate that they have direct correlation to performance and that's just not true. They're internal measuring sticks of meaning only to the optimizer and don't relate to the real world in any significant way. I'd be as clear as possible there. That's another thing I didn't make sufficiently clear in the first edition of my book.

Decent summary of how to read execution plans. Well done. "

Thanks again, Grant, for the encouragement and clarifications.

Darren
OldCursor
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Grant

Thanks, I've already read some of your articles and I got your book just a couple of days ago. I haven't had much time to read it yet - the subject is a bit 'dry' you must admit - but I will very soon!

Thanks
Grant Fritchey
Grant Fritchey
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Ow!

Dry? Now way! I love it. Can't get enough. If you want a quick hit on what to look for in plans, I've got a short list here.

----------------------------------------------------
The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

The Scary DBA
Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
Marcia J
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Grant Fritchey (2/25/2014)

For more, follow the links in my signature below. The Execution Plans book is free as a download from here if you don't want a paper copy.


Bless you!
OldCursor
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Thanks Grant

Now . . . if you enjoy it so much perhaps you could pop round and sort out my clients problems - it would save all that studying.

But unlike most other problems faced by a sql server developer (like how do I find the date of the third Tuesday in the month three months ago etc etc) resolving performance issues can't be achieved simply by a quick search on <insert-the-name-of-your-favourite-search-engine-here> so I guess in that respect it presents a more satisfying challenge (I think).

Your helpful books, articles and tips go a long way to make my efforts a little more successful and therefore more satisfying.

Thanks again
Go


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