1.
Киев 2017
Только реальные кейсы. Только актуальные тренды.
SQL Server Execution
Expectation - Reality
Денис Резник

2.
Киев 2017
About me
• Denis Reznik
• Kyiv, Ukraine
• Data Architect at Intapp, Inc.
• Microsoft Data Platform MVP
• Co-Founder Ukrainian Data Community
• PASS Regional Mentor, Central, and Eastern
Europe
• Author of “SQL Server MVP Deep Dives 2”
Chapter 19
2 |

3.
Киев 2017
Agenda
• Expectation - Reality 1
• Expectation - Reality 2
• Expectation - Reality 3
• Expectation - Reality 4

4.
Parameter Sniffing
Expectation - Reality 1

5.
Киев 2017
EXEC ReportCheckSecurityRequest
@UserId = 1
Query
Processor
SQL Server Cache
Procedure cache
Plan created and cached for the
@UserId = 1
Procedure cache
EXEC ReportCheckSecurityRequest
@UserId = 22
Query executes using the query plan created for
@UserId = 1
Parameter Sniffing - Stored Procedure

6.
Киев 2017
SELECT * FROM Clients WHERE Id = @Id
Query
Processor
SQL Server Cache
Procedure cache
Plan created and cached for the
@Id = 1
Procedure cache
Query executes using the query plan created for
@Id = 1
SELECT * FROM Clients WHERE Id = @Id
sp_executesql N'SELECT * FROM Clients
WHERE Id = @Id', N'@Id int', 1
sp_executesql N'SELECT * FROM Clients
WHERE Id = @Id', N'@Id int', 22
Parameter Sniffing – Parametrized Query

7.
Киев 2017
SELECT * FROM Clients WHERE Id = 1
Query
Processor
SQL Server Cache
Procedure cache
New query plan created and cached. Query
executed using newly created plan.
Procedure cache
SELECT * FROM Clients WHERE Id = 22
New query plan again created and cached. Query
executed using newly created plan.
SELECT * FROM Clients WHERE Id = 1
Query executed using the query plan, created for
the first query.
Procedure cache
Dynamic SQL – Multiple Plans

8.
Index Seek
…
…
1 .. 1M
1 .. 2K 2K+1 .. 4K 1M-2K .. 1M
1 .. 300 301 .. 800 801 .. 1,5K 1,5K+1 .. 2K
SELECT * FROM Users
WHERE Id = 523

9.
Index Scan
…
…
1 .. 1M
1 .. 2K 2K+1 .. 4K 1M-2K .. 1M
1 .. 300 301 .. 800 801 .. 1,5K 1,5K+1 .. 2K
SELECT * FROM Users

10.
DEMO
Parameter Sniffing

11.
Cardinality Estimation
Expectation - Reality 2

12.
Киев 2017
500
1000
10
1200
800
1 800 2000 2800 4500 5400
SELECT * FROM Users
WHERE Id BETWEEN 2100 AND 2500Statistics
SELECT * FROM Users
WHERE Id BETWEEN 10 AND 5300

13.
Киев 2017
500
1000
10
1200
800
1 800 2000 2800 4500 5400
Statistics
SELECT * FROM Users u
INNER JOIN Posts p
ON u.Id = p.OwnerUserId
WHERE u.DisplayName LIKE 'Jeff%'
10600
20000 10
1200 800
A G L S T ZZZZ
Users
Posts

14.
DEMO
Cardinality Estimation

15.
Deadlocks
Expectation - Reality 3

16.
Киев 2017
Lock Types - Shared
S S
X

17.
Киев 2017
Lock Types - Exclusive
X
X
S

18.
Киев 2017
Lock Types - Update
U
U
s
SX
UX
UX

19.
Киев 2017
ID City
1 Kyiv
2 Kharkiv
3 Dnipropetrovsk
BEGIN TRAN
UPDATE Users
SET CityId = 2
WHERE Id = 4
UPDATE City
SET Name = 'Dnipro'
WHERE Id = 3
ID User City_Id
1 John Smith 2
2 Dale Cooper 2
3 Oliver Thompson 2
4 John Dow 3X
BEGIN TRAN
UPDATE City
SET Name = 'Dnipro'
WHERE Id = 3
UPDATE Users
SET CityId = 2
WHERE Id = 4
X
DEADLOCK!
Classic Deadlock

20.
DEMO
Deadlocks

21.
Query Optimization
Expectation - Reality 4

22.
Киев 2017
Query Processing
Parser Procedure
Cache
Algebraizer
Optimizer
Executor

23.
Киев 2017
Optimizer Phase 2 (Last Phase)
Full Set of Optimization Rules
Returns Full Query Plan
• All planned checks were done
• Good Enough Plan was Found
• Timeout
• Not Enough Memory
Optimization

24.
DEMO
Query Optimization

25.
Киев 2017
Summary
• Parameter Sniffing
• Slow in Application. Fast in SSMS.
• Cardinality Estimation
• SQL Server Version Upgrade
• Deadlocks
• Non-Detectable Deadlocks
• Query Optimization
• Query Optimization Timeout

26.
Киев 2017
Thank You!
Denis Reznik
Twitter: @denisreznik
Email: denisreznik@gmail.com
Blog: http://reznik.uneta.com.ua
Facebook: https://www.facebook.com/denis.reznik.5
LinkedIn: http://ua.linkedin.com/pub/denis-reznik/3/502/234