the flavors of non-clustered indexes

The Flavors of Non-Clustered Indexes

Jason Strate

e: jstrate@pragmaticworks.com

e: jasonstrate@gmail.com

b: www.jasonstrate.com

t: StrateSQL

Resources jasonstrate.com/go/indexing

Introduction

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There will be lots of ice cream pictures

Many Flavors

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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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Agenda

Vanilla Sundae Neapolitan

Rocky Road Sugar Cone Gelato

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VANILLA

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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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SINGLE COLUMN

Demo

http://www.flickr.com/photos/cowbite/3452599539/

SUNDAE

Index Intersection

• Leverages multiple non-clustered indexes

• Filters on both indexes

• Returns the “intersection” of both indexes

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Index 1

Index 2

INDEX INTERSECTION

Demo

NEAPOLITAN

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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MULTIPLE COLUMN

Demo

ROCKY ROAD

http://www.flickr.com/photos/stuart_spivack/2069689027/

Included Columns

• 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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INCLUDED COLUMN

Demo

http://www.flickr.com/photos/stuart_spivack/2069689027/

SUGAR CONE

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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FILTERED INDEXES

Demo

GELATO

Foreign Key Indexes

• All foreign keys should be indexed

– Not an index property

• 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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FOREIGN KEYS

SUMMARY

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Summary

• 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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Learn More About Indexes

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For more information…

Name: Jason Strate

Email: jstrate@pragmaticworks.com

Blog: www.jasonstrate.com

Resource: jasonstrate.com/go/indexing