1. When query plans go wrong

2. SQL

3. Simon Sabin Independent SQL Server Consultant and Trainer
Database design and development, Business Intelligence, Performance tuning and troubleshooting
SQL Server since 6.5
Blog:
Twitter: simon_sabin

4. Car crash

5. Works on my computer

6. Parameter Sniffing @

7. SQL tries to be clever

8. A bit like

9. Statistics

10. So what are the root causes

11. Out of date statistics
Best Before: 1/4/1999

12. Skewed data

13. Multi purpose queries

14. Solutions Selective code paths WITH RECOMPILE OPTIMIZE FOR PLAN guides
Careful as SP is compiled as one batch
WITH RECOMPILE
Compilation hit, plan cache bloat
OPTIMIZE FOR
Results in a consistent plan
PLAN guides

15. Update Statistics Update Statistics Trace flag 2388, 2389 and 2390
Can be a performance hit
Trace flag 2388, 2389 and 2390

16. Overview    Out of date statistics Compilation Best Query
Skewed Data
Supportable
Multiple Code paths  
Update statistics 
OPTIMZE FOR
WITH RECOMPILE
Trace Flags

17. Summary You will only know if you monitor Baseline your system
Identify changes in read, writes and cpu
Not duration
Consider the options for your situation
You can win this battle

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Q&A
Now - Just ask
Afterwards – I’ll be around
Much Later
@simon_sabin
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