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SQL Server Query execution. Why my query is slow?
The document discusses SQL Server query execution and outlines common reasons for slow query performance, such as parameter sniffing and network-related waits. It emphasizes various analysis methods, including execution plans and statistics, to diagnose issues. Additionally, it addresses implicit conversion and data type precedence as factors that can affect query speed.
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SQL Server Query execution. Why my query is slow?
- 1. 1 SQL Server Queryexecution. Why my query is slow? Konstantynov Valerii Software engineer
- 2. 2 Agenda 1. How toanalyze query? 1. When a problem can be not in my query. 1. Parameter Sniffing 1. Convert Implicit.
- 3. 33 How to analyzequery? • STATISTICS TIME • STATISTICS IO • Execution Plan • WAITS • SSMS + SQL Profiler
- 4. 44 When a problemit not in my query? Low CPU time - High Duration
- 5. 5 LCK_M_…. WAITS • Occurswhen a task is waiting to acquire a lock. • Example: - Transaction 1: - Transaction 2:
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- 7. 7 ASYNC_NETWORK_IO WAIT • Occurson network writes when the task is blocked behind the network. Verify that the client is processing data from the server. • Example: - Problem with network connection between the server and the client. - Slow processing in the application.
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- 11. 11 Parameter Sniffing SELECT *FROM Customer c WHERE c.EmailAddress = 'petr@gmail.com' Execution Plan SELECT * FROM Customer c WHERE c.EmailAddress = 'ivan@gmail.com' Execution Plan
- 12. 12 Parameter Sniffing EXEC GetCustomers @email='petr@gmail.com' ExecutionPlan EXEC GetCustomers @email='ivan@gmail.com'
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- 14. 1414 Slow in theApplication, Fast in SSMS?
- 15. 1515 The Default SessionSettings
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- 17. 1717 Data Type Precedence 1.user-defined data types (highest) 2. sql_varian t 3. xml 4. datetimeoffset 5. datetime2 6. datetime 7. smalldatetime 8. date 9. time 10. float 11. real 12. decimal 13. money 14. smallmoney 15. bigint 16. int 17. smallint 18. tinyint 19. bit 20. ntext 21. text 22. image 23. timestamp 24. uniqueidentifier 25. nvarchar (including nvarchar(max) ) 26. nchar 27. varchar (including varchar(max) ) 28. char 29. varbinary (including varbinary(max) ) 30. binary (lowest)
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