1. Module 4: Creating and Tuning Indexes

2. Overview Planning Indexes Creating Indexes Optimizing Indexes
Creating XML Indexes

3. Lesson 1: Planning Indexes
How SQL Server Accesses Data
What Is a Clustered Index?
What Is a Heap?
What Is a Nonclustered Index?

4. How SQL Server Accesses Data
Table scan
SQL Server reads all table pages
Index
SQL Server uses index pages to find rows

5. What Is a Clustered Index?
One clustered index per table
B-tree stores data pages in order of index key
sys.partitions id
index_id = 1
root_page
Root Index Page
Intermediate Level Index Pages … …
Leaf Nodes Data Pages … …

6. What Is a Heap? Heap A table without a clustered index
Pages stored in no particular order
sys.partitions id
index_id = 0
first_iam_page
IAM Page
Heap
Data Pages

7. What Is a Nonclustered Index?
B-tree references underlying heap or clustered index
Up to 249 nonclustered indexes per table
sys.partitions id
index_id > 1
root_page
Root Index Page
Leaf Nodes Index Pages … …
Heap or Clustered Index Data Pages … …

8. Lesson 2: Creating Indexes
Overview of Creating Indexes
What Are Unique Indexes?
Considerations for Creating Indexes with Multiple Columns
When to Create Indexes on Computed Columns
What Are Partitioned Indexes?
Options for Incorporating Free Space in Indexes
Methods for Obtaining Index Information
Practice: Creating Indexes

9. Overview of Creating Indexes
CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name ON { table | view } ( column [ ASC | DESC ] [ ,...n ] ) INCLUDE ( column [ ,...n ] ) [WITH option [ ,...n ] ] [ON {partition_scheme (column) | filegroup | "default" } ]
WITH option
Purpose
ALLOW_ROW_LOCKS
Enables/disables row-level locks on index
ALLOW_PAGE_LOCKS
Enables/disables page-level locks on index
ONLINE
Enables/disables access to index during creation
FILLFACTOR
Controls free space on leaf-level pages
PAD_INDEX
Controls free space on non-leaf-level pages

10. What Are Unique Indexes?
Ensures no duplicate values in index key
CREATE UNIQUE NONCLUSTERED INDEX [AK_Employee_LoginID] ON [HumanResources].[Employee] ( [LoginID] ASC)
EmployeeID
LoginID
Gender
MaritalStatus …
216
mike0 M S
231
fukiko0
242
pat0 …
291
pat0 F S …
Duplicate key value not allowed

11. Considerations for Creating Indexes with Multiple Columns
Composite indexes
Include up to 16 columns and 900 bytes in key
Define most unique column first
Included columns
Nonkey columns included in index
Improve query “coverage” and therefore performance
CREATE NONCLUSTERED INDEX K_Contact_LastName_FirstName ON Person.Contact ( LastName ASC, FirstName ASC)
CREATE NONCLUSTERED INDEX AK_Employee_LoginID ON HumanResources.Employee ( LoginID ASC) INCLUDE ( ContactID, NationalIDNumber)

12. When to Create Indexes on Computed Columns
You can create indexes on computed columns when:
Expression is deterministic and precise
ANSI_NULLS connection-level option is ON
Column does not evaluate to the text, ntext, or image data types
Required options are set to ON when index is created and when changes cause index to update
NUMERIC_ROUNDABORT option is set to OFF
Query optimizer might ignore an index on a computed column

13. What Are Partitioned Indexes?
Index is partitioned horizontally by range similar to a partitioned table
sys.partitions id
index_id
partition_number
hobt_id 1 2 …
< 2003
> 2005
Consider alignment with underlying table and inclusion of partitioning key in index key (for unique indexes)

14. Options for Incorporating Free Space in Indexes
Availability of free space affects performance of index updates
FILLFACTOR determines the amount of free space on leaf nodes
Use low FILLFACTOR for OLTP applications
Use high FILLFACTOR for OLAP applications
PAD_FILL determines the amount of free space on non-leaf index nodes
CREATE UNIQUE NONCLUSTERED INDEX [AK_Employee_LoginID] ON [HumanResources].[Employee] ( [LoginID] ASC) WITH ( FILLFACTOR = 65, PAD_INDEX = ON)

15. Methods for Obtaining Index Information
SQL Server Management Studio
Object Explorer
Index Properties window
Reports
System stored procedures
sp_help
sp_helpindex
Catalog views
System functions

16. Practice: Creating Indexes
In this practice, you will:
Create an index by using SQL Server Management Studio
Create an index by using Transact-SQL

17. Lesson 3: Optimizing Indexes
What Is the Database Engine Tuning Advisor?
Practice: Using the Database Engine Tuning Advisor
Index Fragmentation
Options for Defragmenting Indexes
Practice: Defragmenting Indexes

18. What Is the Database Engine Tuning Advisor?
Analyzes database performance under workload
Graphical and command-line interfaces
Workload
Database Engine Tuning Advisor
Reports and Recommendations
Database and Database Objects

19. Practice: Using the Database Engine Tuning Advisor
In this practice, you will:
Use a script of Transact-SQL to analyze indexes in AdventureWorks
Review the index recommendations

20. Index Fragmentation How fragmentation occurs
SQL Server reorganizes index pages when data is modified and causes index pages to split
Types of fragmentation
Internal – Pages are not full
External – Pages are out of logical sequence
Detecting fragmentation
SQL Server Management Studio – Index Properties window
System function – sys.dm_db_index_physical_stats

21. Options for Defragmenting Indexes
<= 30% fragmentation = Reorganize
> 30% fragmentation = Rebuild
ALTER INDEX AK_Product_Name ON Production.Product
REORGANIZE
ALTER INDEX AK_Product_Name ON Production.Product
REBUILD

22. Practice: Defragmenting Indexes
In this practice, you will:
Identify fragmented indexes
Remove fragmentation by rebuilding the index

23. Lesson 4: Creating XML Indexes
What Are XML Indexes?
Types of XML Index
Practice: Creating XML Indexes

24. What Are XML Indexes? Indexes on columns of xml data type
B-tree representation of the nodes in the xml data value
Improve performance because query engine does not need to shred XML data for every query

25. Types of XML Index Index type Description Primary
Clustered B-tree representation of the nodes contained in an xml column
Required to support one or more secondary xml indexes
Secondary
Path
For retrieving data by path and value
Property
For retrieving data by specifying a path
Value
For retrieving data by using imprecise paths

26. Practice: Creating XML Indexes
In this practice, you will:
Record the performance statistics for an XML query
Create a primary XML index
Create a secondary XML index
Investigate the performance statistics for an XML query

27. Lab: Creating and Tuning Indexes
Exercise 1: Creating Indexes
Exercise 2: Tuning Indexes
Exercise 3: Creating XML Indexes