.NET Fest 2017. Денис Резник. Исполнение Запроса в SQL Server. Ожидание - Реальность
- 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
- 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
- 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
- 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