SQL Server Deep Dive, Denis Reznik
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This document provides an overview of how SQL Server processes queries. It discusses the key components like the query processor, parser, algebrizer, optimizer and executor. The query processor breaks queries into logical and physical representations. The optimizer chooses the most efficient execution plan. The executor then runs the query. It also touches on topics like parameter sniffing, locking, deadlocks and the thread pool model.
SQL Server Deep Dive, Denis Reznik
- 1. SQL Server Deep Dive Open Technology Week: .NET Meetup Denis Reznik Data Architect at Intapp, Inc. Microsoft Data Platform MVP
- 2. About Me • Data Architect at Intapp, Inc. • Microsoft Data Platform MVP • PASS Regional Mentor, CEE • Ukrainian Data Community Kyiv Co-Founder • Co-author of “SQL Server MVP Deep Dives vol. 2”
- 3. How We See SQL Server 3 | Some Magic Query Result Set
- 5. SQL Server Network Interface
- 6. SQL Server Protocols • Shared Memory • TCP/IP • Named Pipes • VIA (Deprecated)
- 7. TDS Endpoints TCP/IP Shared Memory Named Pipes VIA DAC TCP/IP Note: TDS – Tabular Data Stream
- 9. Parser Algebrizer Optimizer Executor Query Processing Plan Cache
- 10. Parser • Check if plan is already in cache • Check basic SQL syntax • Returns ParseTree
- 11. Algebrizer • Check that objects are exist and available in current execution context • Define types for every node in ParseTree • Returns QueryTree • Logical representation of the query
- 12. Heap 1 .. 100 100 .. 1k 5K .. 6K 1K .. 5K 6K .. 7K 15K .. 21K 12K .. 15K 10K .. 11K 21K .. 22K 22K .. 41K 9K .. 10K 41K .. 51K 7K .. 8K 8K .. 9K 71K .. 1M 51K .. 71K 1M .. 2M 2M .. 3M
- 13. Clustered Index … … 1 .. 1M 1 .. 2K 2K+1 .. 4K 1M-2K .. 1M 1 .. 300 301 .. 800 801 .. 1,5K 1,5K+1 .. 2K
- 14. 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
- 15. 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
- 16. Index Range 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 WHERE Id BETWEEN 700 AND 1700
- 17. Non-Clustered Index … A .. Z A .. C C .. K X .. Z … 1 .. 1M 1 .. 2K 2K+1 .. 4K 1M-2K .. 1M SELECT * FROM Users WHERE Name = 'Donald Trump' 1 .. 2K 2K .. 4K 1M-2K .. 1M Clustered Index (Id) Non-Clustered Index (Name) Heap
- 18. Extent N Allocation Ordered Scan … 1 .. 1M 1 .. 2K 2K+1 .. 4K 1M-2K .. 1M Clustered Index (Id) Extent 1 Index Allocation Map (IAM) Extent 1 Extent 2 Extent N
- 19. Statistics 500 1000 10 1200 800 1 800 2000 2800 4500 5400 SELECT * FROM Users WHERE Id BETWEEN 2100 AND 2500 SELECT * FROM Users WHERE Id BETWEEN 100 AND 5000
- 20. Optimizer Goal – get the optimal execution plan Optimizer Query Tree Pre-Optimization Search for trivial plan Load statistics (simple) Simplification – syntax transformation
- 21. Optimizer Optimizer Phase 0 Exploration – plan alternatives Return Transaction Processing plan Estimated cost < 0.2 Load statistics
- 22. Optimizer Optimizer Phase 1 Next set of query rules Returns Quick Plan Estimated cost < 1.0 Estimate parallel plan (estimation processed twice)
- 23. Optimizer Optimizer Phase 2 Full optimization Returns Full Plan Indexed views
- 24. Execution Plan != Query Plan SELECT * FROM Users WHERE Id = @id @id = 97 Execution Plan Query Plan Execution Context
- 25. Parameter Sniffing Exec SomeProc @p Optimizer SQL Server Cache Procedure cache@p Plan is cached for the first value of Procedure cache
- 26. Executor • Execute query using its Query Plan • Get needed data from storage engine
- 28. Storage Engine
- 29. Buffer Pool Data Cache Database File Access Methods Buffer Manager Data Selection ? What if I load 2GB value from the disk and read this data using NOLOCK?
- 30. Data Modification Buffer Pool Data Cache Database File Access Methods Buffer Manager Transaction Log Log Manager Log Buffer ? ? Background ProcessesLock Manager ? 3 cases
- 31. Lock Types - Shared S S X
- 32. Lock Types - Exclusive X X S
- 33. Lock Types - Update U U S SX
- 34. Lock Types – Intent locks S ISIS
- 35. DEMO Deadlock
- 36. SQLOS
- 37. Query Execution Model Thread Pool Running Suspended Runnable Scheduler Logical CPU Sleeping (?) Thread (Worker)
- 39. Summary 40 |
- 40. Thank You! Open technology Week: .NET Meetup Denis Reznik Twitter: @denisreznik Email: [email protected] 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