1. Query Tuning Get it Right the First Time Dean Richards Senior DBA, Confio Software1

2. Who Am I? 20+ Years in SQL Server & Oracle
DBA and Developer
Senior DBA for Confio Software
Makers of Ignite8 Response Time Analysis Tools
– only free RTA Tool
Specialize in Performance Tuning
Presented at 24 Hours of PASS
13 SQL Saturdays and counting…

3. Agenda Introduction Which Query Should I Tune? Query Plans
SQL Diagramming
Who registered yesterday for Tuning Class
Lookup paycheck information
Check order status

4. Why Focus on Queries Most Applications Most Queries Why Tune Queries?
Read and Write data to/from database
Simple manipulation and smaller amounts of data
Inefficiencies would not be noticed
Most Queries
Examine larger amounts of data, return a little
Inefficiencies quickly become bottleneck
Why Tune Queries?
“Gives the most bang for your buck”
Changes to SQL are usually safer
~85% of performance issues are SQL related

5. Who Should Tune Developers? DBA? Need a team approach
Developing applications is very difficult
Typically focused on functionality
Not much time left to tune SQL
Do not get enough practice
SQL runs differently in Production than Dev/Test
DBA?
Do not know the code like developers do
Focus on “Keep the Lights On”
Very complex environment
Need a team approach

6. Which SQL User / Batch Job Complaints
Queries Performing Most I/O (LIO, PIO)
Queries Consuming CPU
Queries Doing Table or Index Scans
Known Poorly Performing SQL
Server Side Tracing
Highest Response Times (Ignite8)
SELECT sql_handle, statement_start_offset, statement_end_offset, plan_handle, execution_count, total_logical_reads, total_physical_reads, total_elapsed_time, st.text
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS st
ORDER BY total_elapsed_time DESC

7. Why is SQL Slow – Wait States
Focus on Response Time
Understand the total time a Query spends in Database
Measure time while Query executes
SQL Server helps by providing Wait Types 7

8. Wait Time Tables (SQL 2005/8)
dm_exec_requests
start_time
status
sql_handle
plan_handle
start/stop offset
database_id
user_id
blocking_session
wait_type
wait_time
dm_exec_query_stats
execution_count
total_logical_writes
total_physical_reads
total_logical_reads
total_elapsed_time
dm_exec_query_plan
query_plan
dm_exec_text_query_plan
query_plan
dm_exec_sessions
login_time
login_name
host_name
program_name
session_id
dm_exec_sql_text
text

9. Base Monitoring Query
INSERT INTO SessionWaitInfo SELECT r.session_id, r.sql_handle, r.statement_start_offset, r.statement_end_offset, r.plan_handle, r.database_id, r.blocking_session_id, r.wait_type, r.query_hash, s.host_name, s.program_name, s.host_process_id, s.login_name, CURRENT_TIMESTAMP cdt FROM sys.dm_exec_requests r INNER JOIN sys.dm_exec_sessions s ON s.session_id = r.session_id WHERE r.status <> 'background' AND r.command <> 'AWAITING COMMAND' AND s.session_id > 50 AND s.session_id <>

10. Why is SQL Slow - Plans SQL Server Management Studio
Estimated Execution Plan - can be wrong
Actual Execution Plan – must execute query, can be dangerous in production and also wrong in test
SQL Server Profiler Tracing
Event to collect: Performance : Showplan All
Works when you know a problem will occur
DM_EXEC_QUERY_PLAN,
Real execution plan of executed query

11. DM_EXEC_QUERY_PLAN

12. Case Studies SQL Diagramming Who registered yesterday for Tuning Class
Lookup paycheck information
Check order status

13. SQL Statement 1 Who registered yesterday for SQL Tuning
SELECT s.fname, s.lname, r.signup_date
FROM student s
INNER JOIN registration r ON s.student_id = r.student_id
INNER JOIN class c ON r.class_id = c.class_id
WHERE c.name = 'SQL TUNING'
AND r.signup_date
AND r.cancelled = 'N'
Execution Stats – 9,634 Logical Reads

14. Database Diagram

15. Execution Plan Recommendation from SSMS
CREATE NONCLUSTERED INDEX [<Name of Missing Index>]
ON [dbo].[registration] ([cancelled],[signup_date])
INCLUDE ([student_id],[class_id])

16. SQL Diagramming Great Book “SQL Tuning” by Dan Tow registration
Great book that teaches SQL Diagramming
registration
.03 37
1293 1 1
student
class
.001
select count(1) from registration where cancelled = 'N'
and signup_date between ' :00' and ' :00'
54,554 / 1,639,186 = 0.03
select count(1) from class where name = 'SQL TUNING'
2 / 1,267 = .001

17. New Execution Plan Execution Stats – 9,139 Logical Reads
CREATE INDEX cl_name ON class(name)
Execution Stats – 9,139 Logical Reads
Why would an Index Scan still occur on REGISTRATION?

18. Database Diagram

19. New Execution Plan Execution Stats – 621 Logical Reads
CREATE INDEX reg_alt ON registration(class_id)
Execution Stats – 621 Logical Reads

20. Better Execution Plan Execution Stats – 20 Logical Reads
CREATE INDEX reg_alt ON registration(class_id)
INCLUDE (signup_date, cancelled)
Execution Stats – 20 Logical Reads

21. Alternative from SSMS Execution Stats – 595 Logical Reads
CREATE INDEX reg_can ON registration(cancelled, signup_date)
INCLUDE (class_id, student_id)
Execution Stats – 595 Logical Reads
CREATE NONCLUSTERED INDEX [<Name of Missing Index>]
ON [dbo].[registration] ([class_id],[cancelled],[signup_date])
INCLUDE ([student_id])

22. SQL Statement 2 Paychecks for specific employees
SELECT e.first_name, e.last_name, l.description
FROM emp e
INNER JOIN loc l ON e.loc_id = l.loc_id
WHERE (e.first_name OR e.last_name
AND EXISTS (
SELECT 1
FROM wage_pmt w
WHERE w.emp_id = e.emp_id
AND w.pay_date>= DATEADD(day,-31,CURRENT_TIMESTAMP) )
Execution Stats – 64,206 Logical Reads

23. Database Diagram

24. SQL Diagramming wage_pmt emp loc select count(1) from wage_pmt
.02 90 1
emp
.0005
.0009
1000 1
loc
select count(1) from wage_pmt
where pay_date >= DATEADD(day,-31,CURRENT_TIMESTAMP)
40,760 / 1,915,088 = .02
select top 5 first_name, count(1) from emp
group by first_name order by 2 desc
12 / 23,798 = – first_name
22 / 23,789 = – last_name

25. Execution Plan

26. New Execution Plan
CREATE INDEX ix2_fname ON emp(first_name)

27. Which Index? SSMS Recommendation
CREATE INDEX wp_pay_date ON wage_pmt(pay_date)
INCLUDE (emp_id)
50,000 Logical Reads
or…
Better Option
CREATE INDEX wp_emp_pd ON wage_pmt(emp_id, pay_date)
46 Logical Reads

28. New Execution Plan
CREATE INDEX wp_emp_pd ON wage_pmt(emp_id, pay_date)

29. SQL Statement 3 Lookup order status for caller
SELECT o.OrderID, c.LastName, p.ProductID, p.Description,
sd.ActualShipDate, sd.ShipStatus, sd.ExpectedShipDate
FROM [Order] o
INNER JOIN Item i ON i.OrderID = o.OrderID
INNER JOIN Customer c ON c.CustomerID = o.CustomerID
INNER JOIN ShipmentDetails sd ON sd.ShipmentID = i.ShipmentID
LEFT OUTER JOIN Product p ON p.ProductID = i.ProductID
LEFT OUTER JOIN Address a ON a.AddressID = sd.AddressID
WHERE c.LastName LIKE + '%'
--AND c.FirstName LIKE + '%'
AND o.OrderDate >= DATEADD(day, -30, CURRENT_TIMESTAMP)
AND sd.ShipStatus <> 'C'
Execution Stats – 10,159 Logical Reads

30. Database Diagram

31. Execution Plan

32. SQL Diagramming o i c sd p a
.08
.005 i c
.03 sd p a
SELECT COUNT(1)*1.0/(SELECT COUNT(1) FROM Customer) FROM Customer
WHERE LastName LIKE 'SMI%'
.03
SELECT COUNT(1)*1.0/(SELECT COUNT(1) FROM [Order]) FROM [Order]
WHERE OrderDate >= DATEADD(day, -30, CURRENT_TIMESTAMP)
.08
WHERE OrderStatus <> 'C'
.005
-- Combined

33. Data Skew Problems Only 0.5% of rows are <> ‘C’
SELECT OrderStatus, COUNT(1)
FROM [Order]
GROUP BY OrderStatus
Only 0.5% of rows are <> ‘C’
How about changing the query?
AND o.OrderStatus = 'I'
Add an Index on ShipStatus

34. New Execution Plan Execution Stats – 3,052 Logical Reads
CREATE INDEX IX2_OrderStatus ON [Order] (OrderStatus)
INCLUDE (OrderID,CustomerID)
Execution Stats – 3,052 Logical Reads

35. Takeaway Points Tuning Queries gives more “bang for the buck”
Make sure you are tuning the correct query
Use Wait Types and Response Time Analysis
Locking problems may not be a Query Tuning issue
Wait types tell you where to start
Use “Real Execution Plans”
Get plan_handle from DM_EXEC_REQUESTS
Pass plan_handle to DM_EXEC_QUERY_PLAN()
SQL Diagramming - “Get it right the First Time”
Query Tuner Tools can mislead you

36. Confio Software Wait-Based Performance Tools Igniter Suite
Ignite for SQL Server, Oracle, DB2, Sybase
Helps show which SQL to tune
Based in Colorado, worldwide customers
Free trial at