Microsoft SQL Server Query Tuning

Microsoft SQL Server
Query Tuning
Query Tuning
Speaker: Dean Richards
Senior DBA, Confio Software

Silicon Valley SQL Server User Group
November 2010

Mark Ginnebaugh, User Group Leader,
mark@designmind.com

Query Tuning
Get it Right the First Time
Dean Richards
Senior DBA, Confio Software

2

Who Am I?

 Dean Richards, of course!
,
 20+ Years in SQL Server & Oracle
• DBA and Developer
p
 Senior DBA for Confio Software
• DeanRichards@confio.com
• Makers of Ignite8 Response Time Analysis Tools
• http://www.ignitefree.com – 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
g y y g
• Check order status

4

Why Focus on Queries
 Most Applications
• 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 Q
y 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?
p
• 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
diff tl i P d ti th D /T t
 DBA?
• D not k
Do t know th code lik developers do
the d like d l d
• Focus on “Keep the Lights On”
• Very complex environment

6
 Need a team approach

Which SQL
 User / Batch Job Complaints
 Queries Performing Most I/O (LIO PIO)
(LIO,
 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,
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
8

Wait Time Tables (SQL 2005/8)

http://msdn.microsoft.com/en-us/library/ms188754.aspx

dm_exec_requests dm_exec_query_stats
start_time execution_count
status total_logical_writes
sql_handle total_physical_reads
plan_handle
plan handle total_logical_reads
total logical reads
start/stop offset total_elapsed_time
database_id
user_id
blocking_session dm_exec_query_plan
wait_type
yp query plan
wait_time

dm_exec_text_query_plan
query plan
dm_exec_sessions
login_time
login_name
host_name
dm_exec_sql_text
program_name
program name
text
t t
session_id

9

Base Monitoring Query

INSERT INTO SessionWaitInfo
SELECT r.session_id, r.sql_handle, r.statement_start_offset,
i id l h dl t t t t t ff t
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
sys.dm_exec_requests
INNER JOIN sys.dm_exec_sessions s ON s.session_id = r.session_id
WHERE r.status <> 'background'
AND r.command <> 'AWAITING COMMAND'
d
AND s.session_id > 50
AND s.session_id <> @@SPID

10

Sample Wait Types

 WRITELOG
• Waiting for a log flush to complete
 LCK_M_S, LCK_M_U, LCK_M_X…
• Waiting to acquire locks
 NETWORKIO, ASYNC_NETWORK_IO
• Waiting on the network
 PAGEIOLATCH_SH, PAGEIOLATCH_EX…
• Physical disk reads
 WAITFOR (idle event)
• W i i during a WAITFOR command
Waiting d i d
14

Tracing

 Tracing with waits gathers very good data
 C be High Overhead via Profiler
Can b Hi h O h d i P fil
 Use Server-Side Tracing
• sp_trace_create – create the trace definition
p_ _
• sp_trace_setevent – add events to trace
• sp_trace_setfilter – apply filters to trace
• sp_t ace_setstatus sta t/stop the trace
sp trace setstatus – start/stop t e t ace
 Use Profiler to Create Initial Trace
• Use File > Script Trace to Get Script
 Cumbersome to review data
 Set trace file sizes appropriately

15

Summary of Response Time

 Using Response Time Analysis (RTA) Ensures
you Work on the Correct Problem
 Shows Exactly Why Performance is Suffering
 Helps Prioritize Problems
l bl
 Do Not Rely Exclusively on Health Stats (CPU
Utilization,
Utilization Disk IO Cache Hit Ratio)
IO,
 Data Collection
• DMVs – build it yourself
• Tracing – know how to process trace data
• Tools – Ensure they use Wait Time and Health

16

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
DM_EXEC_QUERY_PLAN,
DM_EXEC_TEXT_QUERY_PLAN(@handle,@s,@e)
• Real execution plan of executed query
p q y

17

Case Studies

 SQL Diagramming
Q g g
• Who registered yesterday for Tuning Class
• Check order status

19

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
i t ti t d t id t d t id
INNER JOIN class c ON r.class_id = c.class_id
WHERE c.name = 'SQL TUNING'
AND r.signup_date BETWEEN @BeginDate AND @EndDate
AND r.cancelled = 'N'

 Execution Stats – 9,634 Logical Reads

20

Execution Plan

Recommendation from SSMS
R d ti f
CREATE NONCLUSTERED INDEX [<Name of Missing Index>]
ON [dbo].[registration] ([cancelled],[signup_date])
INCLUDE ([student_id],[class_id])
([student id] [class id])

22

SQL Diagramming
 Great Book “SQL Tuning” by Dan Tow
• Great book that teaches SQL Diagramming
• http://www.singingsql.com

registration
g .03
37 1293

1 1

student class .001

select count(1) from registration where cancelled = 'N'
and signup_date between '2010-04-23 00:00' and '2010-04-24 00:00'

54,554 / 1,639,186 = 0.03

select count(1) from class where name = 'SQL TUNING
SQL TUNING'

2 / 1,267 = .001
23

New Execution Plan
CREATE INDEX cl_name ON class(name)

 Why would an Index Scan still occur on REGISTRATION?
24

New Execution Plan

CREATE INDEX reg_alt ON registration(class_id)

 Execution Stats – 621 Logical Reads

26

Better Execution Plan

CREATE INDEX reg_alt ON registration(class_id)
INCLUDE (signup_date, cancelled)
(signup date

 Execution Stats – 20 Logicall Reads
d
27

Alternative from SSMS
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])
28
INCLUDE ([student_id])

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 = @fname OR e.last_name = @lname)
AND EXISTS (
SELECT 1
FROM wage_pmt w
t
WHERE w.emp_id = e.emp_id
AND w.pay_date>= DATEADD(day,-31,CURRENT_TIMESTAMP)
)


29

SQL Diagramming

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 = .0005 – first_name
22 / 23,789 = .0009 – last_name
31

New Execution Plan
CREATE INDEX ix2_fname ON emp(first_name)

33

Which Index?
SSMS Recommendation
CREATE INDEX wp pay date ON wage pmt(pay date)
wp_pay_date wage_pmt(pay_date)
INCLUDE (emp_id)

50,000 L i l R d
50 000 Logical Reads

or…

Better Option
CREATE INDEX wp emp pd ON wage pmt(emp id, pay_date)
wp_emp_pd wage_pmt(emp_id, pay date)

46 Logical Reads

34

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

35

SQL Statement 2
 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
It i O d ID O d ID
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 ISNULL(@LastName,'') + '%'
--AND c.FirstName LIKE ISNULL(@FirstName,'') + '%'
AND o.OrderDate >= DATEADD(day, -30, CURRENT_TIMESTAMP)
AND sd.ShipStatus <> 'C'

 Execution Stats – 10 159 Logical Reads
10,159
36

SQL Diagramming
o .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
SELECT COUNT(1)*1.0/(SELECT COUNT(1) FROM [Order]) FROM [Order]
WHERE OrderStatus <> 'C'
.005
-- Combined
.005

39

Data Skew Problems

SELECT OrderStatus, COUNT(1)
FROM [Order]
GROUP BY OrderStatus

 Only 0.5% of rows are <> ‘C’
 How about changing the query?
g g q y
• AND o.OrderStatus = 'I'
 Add an Index on ShipStatus
40

New Execution Plan
CREATE INDEX IX2_OrderStatus ON [Order] (OrderStatus)
INCLUDE (OrderID,CustomerID)
( , )

Execution Stats – 3,052 Logical Reads
41

Takeaway Points

 Tuning Queries gives more “bang for the buck”
 M k sure you are tuning the correct query
Make t i th t
 Use Wait Types and Response Time Analysis
• L ki problems may not be a Query Tuning issue
Locking bl b Q T i i
• 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()
plan_handle DM EXEC QUERY PLAN()
 SQL Diagramming - “Get it right the First Time”
• Query Tuner Tools can mislead you

Confio Software

 Wait-Based Performance Tools
 Igniter Suite
• Ignite for SQL Server, Oracle, DB2, Sybase
g Q , , , y
• Ignite for Databases on VMWare (Beta)
 Helps show which SQL to tune
 Provides visibility into entire stack
 Based in Colorado, worldwide customers
,
 Free trial at www.confio.com

43

To learn more or inquire about speaking opportunities, please contact:

Mark Ginnebaugh, User Group Leader
mark@designmind.com

http://www.meetup.com/The‐SiliconValley‐SQL‐Server‐User‐Group/

Microsoft SQL Server Query Tuning

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