1. SQL Server
Parallel Processing
for Pros

2. Agenda
• Parallel Processing Concepts
• Single Query Optimization
• Workload Optimization

3. Parallel Processing
How does it Work ?

4. Preemptive Scheduling
Thread 1
CMD
CMD
Core Scheduler CMD
Thread 2
CMD
CMD
CMD
Thread 3
CMD
CMD
Context Switch
CMD

5. How does it work in SQL Server
Thread Pool
(Workers) Tasks Batch
CPU Core
SELECT …
Task Read…
…..
Read… …..
Write…
UPDATE …
….
Calculate… ….
Write…
Pending Tasks
Scheduler
Max Workers !!

6. CPU Scheduling
Runnable Queue Suspended (Waiting) Tasks
CPU Core IO_COMPLETION
Read…
LCK_M_X
Calculate…
Write…
Scheduler Running Task - Worker
Pending Tasks
Read…
Write…

7. Now you own the
Parallelism Matrix !

8. What about the
1 Million Dollar Question ?

9. What degree of parallelism
(DOP) is optimal ?

10. Parallel System Configuration
• MAXDOP
• Cost Threshold for Parallelism
• Max Workers

11. Parallel System Configuration
• MAXDOP
• Cost Threshold for Parallelism
• Max Workers

12. MaxDop
• Default
• Microsoft Recommendation
• Other Recommendations:
Start with Cores / 3 - Cores / 2 and
check CXPACKET

13. MaxDop – What people do?
http://www.sqlskills.com/BLOGS/PAUL/post/M
AXDOP-configuration-survey-results.aspx

14. Waits – What people have?
http://www.sqlskills.com/BLOGS/PAUL/post/W
ait-statistics-or-please-tell-me-where-it-
hurts.aspx

15. MaxDop
• It’s only a hint, SQL Server might still choose
a serial plan
• Change of MAXDOP setting for the
server, will flush the plan cache.

16. Parallel System Configuration
• MAXDOP
• Cost Threshold for Parallelism
• Max Workers

17. Cost Threshold for Parallelism
• Default (5)
• Other Recommendations:
5 is too low, Get it higher to 50
Jonathan Kehayias Recommendation

18. My Recommendation
It really depends on your workload, you need
to first test:
For OLTP have
• Higher Cost Threshold (50)
• Start with low MAXDOP (8-12)
For OLAP have
• Higher Cost Threshold (50)
• Start with high MAXDOP (Cores / 2)

19. My Recommendations
Run Jonathan Kehayias Script to tune Cost
Threshold for Parallelism.
Run a trace, change MAXDOP, rerun a trace
on the same workload and run Qure
Analyzer (Free !) until you find the perfect
MAXDOP.
Override MAXDOP if necessary (Use Plan
Guides):
• In OLTP override with a higher MAXDOP.
• In OLAP override with a lower MAXDOP.

20. Become a true Pro !
Join one of our courses:
 SQL Server 2012 – Guy Glantser
 Storage for DBAs – Tzahi Hakikat
 Advanced Programming in SQL Server – Noam Brezis
Contact Us:
www.madeira.co.il

21. Thank you
To:
• Guy Glantser (Madeira)
• Haim Fishner (Madeira)
• Adam Machanic
• R Meyyappan (http://www.sqlworkshops.com/)
Contact Us:
www.madeira.co.il

22. Thank You!
Noam Brezis
Email:
noam@madeira.co.il
Website:
www.madeira.co.il