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Mastering SQL Indexing: Clustered, Non-Clustered, and Filtered Indexes Demystified

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garvey
22 diapositives · 318 Views · Jul 29, 2014

Dive deep into the world of SQL indexes with expert Denny Cherry. Learn the internals of clustered, non-clustered, and filtered indexes, and understand the structures and navigation techniques within B-trees. Unlock the keys to optimizing SQL query performance. Follow along with real examples and visual explanations to enhance your SQL indexing skills.

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Mastering SQL Indexing: Clustered, Non-Clustered, and Filtered Indexes Demystified
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  1. Indexing Internals Denny Cherry mrdenny@mrdenny.com twitter.com/mrdenny

  2. About Me • Author or Coauthor of 4 books • 8+ SQL Mag articles • Dozens of other articles • Microsoft MVP since Oct 2008 • Microsoft Certified Master • Founder of SQL Excursions • Independent Consultant

  3. What we’ll be covering… • Clustered Indexes • Non-Clustered Indexes • Filtered Indexes

  4. What we won’t be covering… • Spatial Indexes • Full Text Indexes • Compressed Indexes • Columnar Store Index

  5. Structures… • Indexes are made up of B-Trees which make the index navigable • Indexes are almost always made up of at least two data pages. • A Root Page • A Leaf Page • Clustered Indexes also have Data Pages • Lets look at a pretty picture…

  6. Clustered Index

  7. Clustered Index Data Page • Contains one row for every row in the table • Contains all in row data • Contains pointers to out of row data • TEXT • NTEXT • IMAGE • Contains pointers to overflow data • XML • VARCHAR(MAX) • NVARCHAR(MAX) • VARBINARY(MAX)

  8. Slot Array • Shows what row within the page each row occupies • Contains the Clustered Index value and row id only

  9. Clustered Index Intermediate Levels • Contains one row, for each page below it • Each row contains… • Clustered Key Value • File Id (2 bytes) • Page Id (4 bytes) • Row Overhead (At least one byte) • Slot array location within this page (2 bytes)

  10. Row Overhead? • 1 Byte by default • Nulls? • Variable Width Data Types?

  11. Clustered Index Root Page • Only a single root page can exist • Contains one row, for each page below it • Each row contains… • Clustered Key Value • File Id (2 bytes) • Page Id (4 bytes) • Row Overhead (At least one byte) • Slot array location within this page (2 bytes)

  12. Navigating The Clustered Index

  13. Splitting the Root Page

  14. Uniqueifier … • Non-Unique clustered indexes have an extra column called the uniqueifier which ensures that values within the index are unique. • Uniqueifier is only used for rows which are not unique.

  15. Non-Clustered Index

  16. Nonclustered Index Intermediate Page • Contains one row for every row in the table • Contains indexed value and clustered index key or RID

  17. NonClustered Index Root Page • Only a single root page can exist • Contains one row, for each page below it • Each row contains… • Indexed Key Value • Clustered Key Value or RID (if index is not unique) • File Id (2 bytes) • Page Id (4 bytes) • Row Overhead (At least one byte) • Slot array location within this page (2 bytes)

  18. Navigating The NonClustered Index

  19. Navigating The Clustered Index

  20. B-Tree Sizes • Each B-Tree page can store info about X child pages… • INT = 8096/13 bytes = 622 pages • BIGINT = 8096/17 bytes = 476 pages • GUID = 8096/25 bytes = 323 pages

  21. Sample Index Size Sample table has a clustered key which is an Integer. • Root Level = 1 page • Intermediate Level = 7 pages • Data Pages = 11233 pages • Another page level requires 7,650,600 data pages for a fourth level

  22. Denny Cherry mrdenny@mrdenny.com http://itke.techtarget.com/sql-server Please fill out the survey at http://speakerrate.com/mrdenny.