1. Reading Execution Plans Successfully
Arthur Daniels
Reading Execution Plans Successfully

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4. Arthur Daniels Twitter: ArthurDanSQL www.DBA-Art.com
Database Administrator
SAP Fieldglass
Focuses on performance tuning
“I don’t care how long my query takes as long as it returns results”

5. Overview Structure of the plan First operators
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Overview
Structure of the plan
First operators
Warnings and suggestions
Manipulating an execution plan

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Disclaimer:
SQL Server 2014 and above AdventureWorks 2014

7. Your environment matters
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Your environment matters
Hardware
SQL Settings
Min and max memory
Cost threshold for parallelism
Max DOP
SQL version

8. Structure: Graphical Execution Plan
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Structure: Graphical Execution Plan
What’s that?

9. Other execution plan features
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Other execution plan features
Flow and size of line

10. Graphical Execution Plan
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Graphical Execution Plan
Plan Operators
Index Seek Index Scan Key Lookup

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Where and what are they?
Graphical Execution Plans are stored as XML SQL Server Management Studio (SSMS) Live Query Stats SQL Server Plan Cache Query Store?

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The Plan Cache
sys.dm_exec_cached_plans (2008) Plan cache contains estimates Emptied when server restarts

13. Plan cache demo Build plan cache Find our specific plan
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Plan cache demo
To-do:
Build plan cache
Find our specific plan
Look at operator
View actual plan’s rows vs estimated.

14. Where do the estimates come from?
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Where do the estimates come from?
SQL Server automatically generates statistics
One statistic per index
One statistic per column once a query searches by that column
Search as in Where clause, JOINs

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Statistics Demo
Open Statistics on IX_TransactionHistoryArchive_ProductID

16. Statistics General Used for execution plan estimates
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Statistics General
Used for execution plan estimates
Automatically generated
One for each index
One for each column*
Statistics contain header, density vector and histogram

17. Warnings and Suggestions

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Implicit Conversion
Why? In actual and estimated

19. Reading Implicit Conversions
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Reading Implicit Conversions
Demo

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Missing Index Hints
Execution plan will contain index suggestions Only the first missing index is shown Review missing index DMVs

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Missing Indexes
Demo

22. Manipulating an execution plan
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Manipulating an execution plan
Parallelism as operators
Gather Streams Distribute Streams Repartition Streams

23. Comparing a parallel query to serial query
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Comparing a parallel query to serial query
Demo Set Cost Threshold for Parallelism to 1 for this demo

24. Conclusion Look at the warnings Start with the right side of the plan
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Conclusion
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Look at the warnings
Start with the right side of the plan
Read the predicates to understand the operator
Try to re-write the query

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Questions?
You can also contact me on or my website,

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Useful links
Finding Implicit Conversions in your Plan Cache Free graphical plan explorer: