Choosing Your Clustered Index

Choosing Your Clustered Index

Jason Strate

e: [email protected]

e: [email protected]

b: www.jasonstrate.com

t: StrateSQL

Resources jasonstrate.com/go/indexing

Introduction

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Agenda

Introduction Clustered Index or Heap

Clustered Index Qualities

Clustered Index Patterns

Summary


Session Goals

• Define basics related to clustered indexes

• Explain rules behind selecting clustering key

• Demonstrate differences between key column choices


CLUSTERED INDEX OR HEAP

IntroductionClustered Index or

Heap

Clustered Index

Qualities

Clustered Index

PatternsSummary


Heap Structure

• Pile of data

– Unordered

– First in, first out

– Scan “happy”


Heap


Heap


Clustered Index

• Mechanism for storing data

– Ordered

– Structured

– Accessible

– Direct path


Clustered Index


Clustered Index


DEMOClustered Index or Heap


Pro Tip: Default to Clustered Indexes, unless heaps are proven to improve performance

CLUSTERED INDEX QUALITIES


Heap

Clustered Index

Qualities

Clustered Index

PatternsSummary



Static Narrow

UniqueEver-

increasing



Static Narrow

UniqueEver-

increasing



Static Narrow

UniqueEver-

increasing


Narrow

Size

Rows 4 8 16 32 64

10,000 0.04 0.08 0.15 0.31 0.61

100,000 0.38 0.76 1.53 3.05 6.10

1,000,000 3.81 7.63 15.26 30.52 61.04

10,000,000 38.15 76.29 152.59 305.18 610.35

100,000,000 381.47 762.94 1,525.88 3,051.76 6,103.52

1,000,000,000 3,814.70 7,629.39 15,258.79 30,517.58 61,035.16



Static Narrow

UniqueEver-

increasing


Unique

• Uniqueifier

Size

Rows 4 8 16 32 64

10,000 0.08 0.11 0.19 0.34 0.65

100,000 0.76 1.14 1.91 3.43 6.48

1,000,000 7.63 11.44 19.07 34.33 64.85

10,000,000 76.29 114.44 190.73 343.32 648.50

100,000,000 762.94 1,144.41 1,907.35 3,433.23 6,484.99

1,000,000,000 7,629.39 11,444.09 19,073.49 34,332.28 64,849.85



Static Narrow

UniqueEver-

increasing


Ever-Increasing

1 2 3 4 5 6


Ever-Increasing

1 3 5 6 2 4


Ever-Increasing

1 2 3 4 5 6


These are not unbreakable rules!

CLUSTERED INDEX PATTERNS


Heap

Clustered Index

Qualities

Clustered Index

PatternsSummary


Clustered Index Patterns

Identity Column

Surrogate Key

Foreign KeyMulti-

Column

Globally Unique

Identifier


Identity Column

• Non-related value that defines each row uniquely

• Assigned when data is inserted

• Typically uses:

– Int or bigint

– IDENTITY or SEQUENCE


Identity Column

Static

Narrow

Unique

Ever-increasing


DEMOIdentity Column


Surrogate Key

• Unique value is a part of the row

• Assigned in the source data

• Data type dependent on the data

• Value should be unchanging

– Employee ID

– Social Security Number

– Birthdate


Surrogate Key

Static

Narrow

Unique

Ever-increasing


DEMOSurrogate Key


Foreign Key

• One-to-many relationships

• Access path in child via parent

• Piggy-backs identity pattern

– Parent left of child identity value

• Common in many applications

– Order header to details

– Hotels to rooms


Foreign Key

Static

Narrow

Unique

Ever-increasing


DEMOForeign Key


Multi-Column

• Similar to foreign key pattern

• Many-to-many relationships

• Highly dependent on selectivity

• NOT a collection of dimension keys


Multi-Column

Static

Narrow

Unique

Ever-increasing


DEMOMulti-Column


Globally Unique Identifier

• Non-related value that defines each row uniquely

• Assigned when data is inserted

– Or from the application

• Typically uses:

– uniqueidentifier

– NEWID() or NEWSEQUENTIALID()


Globally Unique Identifier

Static

Narrow

Unique

Ever-increasing


DEMOGlobally Unique Identifier


Pro Tip: Clustered indexes should be Static, Narrow, Unique, and Ever-increasing

SUMMARY


Heap

Clustered Index

Qualities

Clustered Index

PatternsSummary


Summary

• Clustered indexes are important

• Select clustering keys based on need

• Validate clustered indexes over time


More Information

Expert Performance IndexingFor SQL Server 2012

Jason StrateTed Krueger

OverviewStatistics

MaintenanceTools

Analysis

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Name: Jason Strate

Email: [email protected]

Blog: www.jasonstrate.com

Resource: jasonstrate.com/go/indexing

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Choosing Your Clustered Index