A non-clustered index is just another way to get to data. Add in a couple columns and off you go. Not too much to think about, just fire and forget. But it’s not really that easy. Non-clustered indexes have a number of various ways in which they can be built and designed that can have significant impacts on performance. In this session we’ll look at what can go into a non-clustered index. We will explore what you can put into a non-clustered index and what you can expect back out from performance.
3. About Pragmatic Works
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9. Non-Clustered Indexes
• Sorted key values
– One or more columns
– Key values only
– Pointers to Heap or
Clustered Index rows
– Non-LOB data
• Secondary data access
– Bridge to the data
• Operations
– Index scan
– Index seek
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12. Single Column Index
• Provides a secondary path to data
• Allows alternative paths for finding data
• One column is stored outside table
– Data is sorted by key
– Includes clustered index keys
• Focus on most used columns for filters
• Do not index every column
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15. Index Intersection
• Leverages multiple non-clustered indexes
• Filters on both indexes
• Returns the “intersection” of both indexes
Index
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Index
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18. Multiple Column Index
• Two or more columns in the same index
• Index sorted from left to right
– Cannot skip columns to leverage sort
• Cover filters over multiple columns
– Or cover non-filtered columns
• Reduces number of indexes needed
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21. Included Columns
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Additional columns needed for queries
Typically data not included in index
Included columns brings in data pages
Store specific columns unsorted with index
Don’t included all columns
– Or even most
• Be cautious of update rate of data
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24. Filtered Indexes
• Add a WHERE clause to your index
• Changes the contents of the index
– Reduction in pages
– Reduction in size
– Lessen impact of index scan
• Unmatched Index warning
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27. Foreign Key Indexes
• All foreign keys should be indexed
– Not an index property
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Constraint leverages sorts on validation
Can reduce locking, blocking, and deadlocks
Common problem in many systems
Silent killer of the database
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30. Summary
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You can get by on “vanilla” indexes
Indexes can vary in flavors
These flavors help improve your databases
Filtered indexes, included columns, and
multiple columns
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31. Learn More About Indexes
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32. For more information…
Name: Jason Strate
Email: jstrate@pragmaticworks.com
Blog: www.jasonstrate.com
Resource: jasonstrate.com/go/indexing
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