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Planning and Creating Index
Vu Tuyet [email protected]
Hanoi University of Technology
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Outline
Introduction to Indexes
Understanding Index Architecture
Retrieving Stored Data with SQL Server Defining Indexes
Creating Indexes
Maintaining Index
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Index
Data storage Rows are stored in data pages Heaps are a
collection of data pages for a table
Data access Scanning all data pages in a table Using an index
that points to data on a page
Data Pages
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Creating Index or not ?
Creating index
Speeds up data access
Enforces uniqueness of rows
Donot creating index
Consumes disk space Incurs overhead
Primary and foreign keys
Frequently searched in ranges
Frequently accessed in sorted order
Seldom referenced in queries
Containing few unique values
Defined with bit, text, orimage data
types
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Index Architecture
How SQL Server Uses Indexes
Maintaining Heaps
Using Clustered Indexes Using Nonclustered Indexes
Accessing a Range of Data in a Heap
Accessing a Range of Data with Clustering Keys
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How SQL Server Uses Indexes
1. Determining if index exists on an appropriate column for the
query
2. If an index does not exist
Scanning each data page of the table.
3. If an index exists,
Determining whether that index is useful for retrieving the
desired data.
3.1 If the index is useful,
SQL Server then uses it to access the rows in the table
3.2 If the index is not user full database
Scanning each data page in table
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Maintaining Heaps
Using index allocation map pages
Containing information on where the extents of a heap
are stored
Navigating through the heap and find available space for newrows
being inserted
Connecting data pages
Reclaiming space for new rows in the heap when a row
isdeleted
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Using Clustered Indexes Each table can have only one clustered
index
The physical row order of the table and the order of rowsin the
index are the same
Key value uniqueness is maintained explicitly or implicitly
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Using Non-clustered Indexes
Non-clustered indexes are the SQL server default
Existing non-clustered indexes are automatically rebuilt
when:
An existing clustered index is dropped
A clustered index is created
The DROP_EXISTING option is used to change which columns
define the clustered index
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Accessing a Range of Data in a Heap
Data Pages
Page 7 Page 8 Page 9
Akhtar
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470604
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470703...
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470802
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470804
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Index Pages
Non-leafLevel
Page 12 - RootPage 37 Page 28
Leaf Level
(Key Value)
Page 41 Page 51 Page 61 Page 71
Akhtar...Martin
AkhtarBarrConFunkFunk
470601470503470401470602470402
MartinMartin
OtaPhuaRudd
470801470604470702470802470501
MartinSmith...
SmithSmithSmithWhiteWhite
470603470804470701470403470502
AkhtarGanio...
GanioHall
JonesJonesJones
470901470904470902470803470703
SELECT lastname, firstanme
FROM member
WHERE lastname
BETWEEN 'Martin' AND 'Rudd'
Data Pages
Page 7 Page 8 Page 9
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470503...
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470703...
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Phua
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470802
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470804
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470902
470904...
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Index Pages
Non-LeafLevel
Page 12 - RootPage 37 Page 28
Leaf Level
(Key Value)
Page 41 Page 51 Page 61 Page 71
Akhtar...Martin
AkhtarBarrConFunkFunk
470601470503470401470602470402
MartinMartin
OtaPhuaRudd
470801470604470702470802470501
MartinSmith...
SmithSmithSmithWhiteWhite
470603470804470701470403470502
AkhtarGanio...
GanioHall
JonesJonesJones
470901470904470902470803470703
Martin
Martin
Martin 470801Martin 470604Ota 470702Phua 470802Rudd 470501
Martin ... 470801Phua ... 470802Ota ... 470702
Martin ...470604
Rudd ... 470501
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Accessing a Range of Data in Clustering Key
1234
Index
Pages
Non-leaf
LevelPage 12 - Root1234...
5678Page 3712342234...
Page 2856787678...
Page 41 Page 61
56785778
587859786078
BarrSmith 8721
OtaJones 5788Rudd
Page 71
76787778
787879788078
GanioMartin 7206
PhuaSmith 8772Hall
Page 51
22342334
243425342634
WhiteAkhtar
JonesConJones6002
Leaf Level
(Key Value)
Clustered
IndexAkhtar...Martin
Page 140 - Root
Page 100 Page 110 Page 120 Page 130
1234
23345678253413341534
...
AkhtarBarrConFunkFunk
...
...
...
...
...
...
...
4705
...
76788078243459782634
...
GanioHallJonesJonesJones
...
...
...
...
... 5788
...
...
6002
...
AkhtarGanio...
Page 141
12347778587878786078
...
MartinMartinOtaPhuaRudd
...
...
... 7206
...
...
...
... ...
14345778797822341634
...
SmithSmithSmithWhiteWhite
...
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... 8721
... 8772
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9355
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Page 145
1334
143415341634
MartinFunk
SmithFunk4705White9355
Martin
SELECT lastname, firstanme
FROM member
WHERE member_no
BETWEEN 5678 AND 6078
Smith...
1234
Index
Pages
Non-Leaf
LevelPage 12 - Root1234...
5678Page 3712342234...
Page 2856787678...
Page 41 Page 61
56785778
587859786078
BarrSmith 8721
OtaJones 5788Rudd
Page 71
76787778
787879788078
GanioMartin 7206
PhuaSmith 8772Hall
Page 51
22342334
243425342634
WhiteAkhtar
JonesConJones6002
Leaf Level
(Key Value)
Clustered
IndexAkhtar...Martin
Page 140 - Root
MartinSmith...
Page 100 Page 110 Page 120 Page 130
1234
23345678253413341534
...
AkhtarBarrConFunkFunk
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4705
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76788078243459782634
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GanioHallJonesJonesJones
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... 5788
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6002
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AkhtarGanio...
Page 141
12347778587878786078
...
MartinMartinOtaPhuaRudd
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... 7206
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14345778797822341634
...
SmithSmithSmithWhiteWhite
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... 8721
... 8772
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9355
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Page 145
1334
143415341634
MartinFunk
SmithFunk4705White9355 6078 Rudd
56785778
58785978
BarrSmith 8721
OtaJones 5788
5678
5678
Martin
Akhtar
MartinSmith
6078 Rudd ...
5878 Ota ...5778 Smith ... 87215678 Barr ...
5978 Jones ... 5788
AkhtarGanio...
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Managing Indexes
Creating Indexes
Creating Unique Indexes
Creating Composite Indexes Obtaining Information on Existing
Indexes
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Creating Index
Using the CREATE INDEX Statement
USE library
CREATE CLUSTERED INDEX cl_lastnameON library..member
(lastname)
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Creating Unique Indexes
USE library
CREATE UNIQUE INDEX title_identON title (title_no)
12 Le Petit Prince Antoine de Saint-Exupery ~ ~ ~
Duplicate key values are not allowedwhen a new row is added to
the table
title
title_no title author synopsis
1011
12
The Night-BornLemon
Walking
Jack LondonMotojirou
Henry David Thoreau
~ ~ ~~ ~ ~
~ ~ ~12 Walking Henry David Thoreau ~ ~ ~
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Creating Composite IndexesUSE library
CREATE UNIQUE INDEX loan_identON loan (isbn, copy_no)
Composite Key
Column 1 Column 2
loan
isbn copy_no title_no member_no
342
342
343
5
10
4
35
35
35
3744
5278
3445
out_date
1998-01-06
1998-01-04
1998-01-04
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Creating Index Option
Using the FILLFACTOR option
Using the PAD_INDEX option
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Using the FILLFACTOR Option
Specifies how much to fill the page
Impacts leaf-level pages
Data Pages Full
Con
Funk
WhiteRudd
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470401
470402
470403470501
White ... 470502Barr ... 470503
Akhtar
Funk
SmithMartin
Smith
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470601
470602
470603470604
470701Ota ... 470702
Martin
Phua
JonesSmith
Ganio
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470801
470802
470803470804
470901Jones ... 470902
Data Pages
50% Fillfactor
ConFunkWhite
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470401470402470403
RuddWhiteBarr
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470501470502470503
AkhtarFunkSmith
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470601470402470603
MartinSmithOta
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470604470701470702
MartinPhuaJones
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470801470802470803
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470804470901470902
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Using the PAD_INDEX Option Specifies percentage to which to fill
index page
Must use with FILLFACTOR option
Impact Non-Leaf-Level Index pages
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Obtaining Information on Existing Indexes
Using the sp_helpindex system stored procedure
Using the sp_help tablename system storedprocedure
USE library
EXEC sp_helpindex member
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CREATE CLUSTERED INDEX loan_identON loan (isbn, copy_no)
WITH DROP_EXISTING, FILLFACTOR=65
DROP_EXISTING Option
Rebuilds an index Can change index characteristics Reorganizes
leaf pages Recalculates index statistics
Changing index characteristics Type Index columns Options
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Maintaining Indexes
Data fragmentation
Index tuning wizard
DBCC SHOWCONTIGStatement
DROP_EXISTING Option
Statistical information
Index analysis
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Data Fragmentation
How fragmentation occurs SQL Server reorganizes index pages when
data is modified Reorganization causes index pages to split
Managing fragmentation Dropping and recreating an index and
specifying a fillactorvalue Rebuild an index and specify a
fillfactorvalue
Business environment
Data fragmentation can be good for OLTP environment Data
fragmentation can be bad for OLAP Services environment
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Index Tuning Wizard Capturing a workload
Analyzing a workload
Providing an indexing recommendation Implementing an indexing
recommendation
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DBCC SHOWCONTIG Statement DBCC SHOWCONTIG determines
whether a table or index is heavily fragmented
whether data and index pages are full
Executing DBCC SHOWCONTIG
If tables have been heavily modified
If tables contain imported data
If tables seem to cause poor query performance
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Describes distribution of data in a column for use by
query optimizer
Automatically maintained
Statistics creation
Automatic for indexed columns
Can be created for other columns
USE libraryCREATE STATISTICS STATS_outdateON loanhist
(out_date)
Statistical Information
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Using the UPDATE STATISTICSStatement
Obtaining statistic information
Disabling the automatic updating of statistics
USE library
UPDATE STATISTICS loan loan_ident
Updating Statistics
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Index Analysis
Using the SHOWPLAN statement Indicating whether an index is
used
Displaying summary or detailed information about a query
Using the STATISTICS IOStatement Indicating the amount of I/O
used to return the result set
Displaying information on the logical and physical I/O for
aspecific query
Using graphical SHOWPLAN
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Used in development environment
Specifying how to access data
Overriding the query optimizer
USE library
SELECT title_no, title, author
FROM title WITH (INDEX(author_ind))WHERE author = 'Jane
Austen'
Optimizer Hints
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Performance Considerations Creating indexes on foreign keys
Creating clustered indexes before nonclustered indexes
Creating composite indexes Creating multiple indexes for a table
frequently read
Use the Index Tuning Wizard
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Ramarks
Choose the appropriate columns to index
Use the FILLFACTOR and PAD_INDEX options to
optimize performance
Use the DROP_EXISTING option to rebuild indexes
Execute DBCC SHOWCONTIG to measure fragmentation
Avoid optimizer hints
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![Index [assets.cambridge.org]assets.cambridge.org/97805211/95591/index/9780521195591...Index ... Index Index](https://img.pdfslide.net/doc/110x75/60d574a113c9786842650971/-index-index-index-index.jpg)
