The document discusses troubleshooting execution plan changes in SQL Server 2016, emphasizing the use of the Query Store and various methods to detect plan recompilation. It outlines reasons why execution plans may need recompilation and suggests techniques such as plan guides to stabilize execution plans. The content is aimed at SQL Server users and includes references for further study on plan caching and reuse.

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Troubleshooting Plan Changes with
Query Store in SQL Server 2016

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John Sterrett
@johnsterrett
John.Sterrett@linchpinpeople.com
Johnsterrett.com
linked.com/in/johnsterrett
google.com/+johnsterrett
Specialties / Focus Areas / Passions:
• Performance Tuning &
Troubleshooting
• Virtualization
• Infrastructure
• Architecture
• High Availability
• Disaster Recovery
• Health Monitoring
• Capacity Management
• License Efficiency
Linchpin People Group Principle
Leader Austin SQL
Server User Group
Leader Virtual Chapter
“High Availability and
Disaster Recovery”
PASS Regional Mentor

3. Life of an Execution Plan
Execute T-SQL
Does A Execution
Plan Exist?
Use The Execution Plan
in Cache
Yes, It Exists
Build Execution Plan
with Variables Used at
Runtime
No, Plan Doesn t Exist
Put Execution Plan in
Cache
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4. How Do I Detect Plan Recompile?
• Profiler
• Extended Events
• Dynamic Management Views (DMVs)
• Query Store (SQL Server 2016)
• TechNet – Execution Plan Caching and Reuse
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5. Reasons for Execution Plan Recompiles
• Changes made to a table or view referenced by the query (ALTER TABLE and ALTER VIEW).
• Changes made to a single procedure, which would drop all plans for that procedure from the
cache (ALTER PROCEDURE).
• Changes to any indexes used by the execution plan.
• Updates on statistics used by the execution plan, generated either explicitly from a statement,
such as UPDATE STATISTICS, or generated automatically.
• Dropping an index used by the execution plan.
• An explicit call to sp_recompile.
• Large numbers of changes to keys (generated by INSERT or DELETE statements from other users
that modify a table referenced by the query).
• For tables with triggers, if the number of rows in the inserted or deleted tables grows
significantly.
• Executing a stored procedure using the WITH RECOMPILE option.
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6. DEMO!
• Capture Execution Plan information
• Identify Queries with Changing Plans
• Learn how to freeze a plan with Plan Guides
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7. References
• Plan Guides (plan freezing) in SQL Server 2005/2008
• Plan Guides on Books Online
• Execution Plan Caching and Reuse

8. The SQL Server 2016 Solution….
8

9. Query Store!
9

10. DEMO!
• Query Store in SQL Server 2016
• Find Top Offenders
• Identify Changing Execution Plans
• Easily Freeze an Execution Plan
• Internal DMVs
10

11. References
• Plan Guides (plan freezing) in SQL Server 2005/2008
• Plan Guides on Books Online
• Execution Plan Caching and Reuse
• Monitor Performance With Query Store (SQL 2016)