SQL Server Indexing for the Client Developer
Table Indexing for the .NET DeveloperDenny
[email protected]/mrdenny
About MeIndependent ConsultantFounder of SQL ExcursionsAuthor or
Coauthor of 5 books8+ SQL Mag articlesDozens of other
articlesMicrosoft MVPMicrosoft Certified MasterVMware vExpert2
Todays GoalsIntroduce the different kinds of indexesCommon
Misconceptions about indexesDownsides to indexesIntroduce advanced
index tuning techniquesQ & ATodays GoalsIntroduce the different
kinds of indexesCommon Misconceptions about indexesDownsides to
indexesIntroduce advanced index tuning techniquesQ & ADifferent
Kinds of IndexesFive Kinds of IndexesClusteredNon-clusteredFull
TextXMLColumnStore IndexesTheres new stuff coming in SQL Server
2012Semantic SearchClustered Indexes1 Clustered Index per
tableContain Full Copy of row data within in the indexUp to 16
indexed columns can be part of the index(15 if the table contains
any XML indexes)Primary Key will by default be the Clustered
IndexMust be created on the same filegroup as the tableClustered
Indexes should be as narrow as possibleWhile not required, they are
highly recommendedNon-clustered IndexUp to 999 per table Starting
with SQL Server 2008255 in SQL Server 2005 and belowUp to 16
indexed columns in the indexNon-indexed columns can be included via
INCLUDE statementNon-Clustered indexes always contain the clustered
index columns (when table has a clustered index)When table is a
heap, the Row ID is stored in every non-clustered index.Can be
created on any filegroup within the databaseCan be filtered indexes
to include fewer rows in the index.
The number of indexes has not been changed as of SQL Server 2012
CTP37Differences between unique and non-unique clustered
indexesNon-Unique clustered indexes have an extra column called the
uniqueifier which ensures that values within the index are unique.
Uniqueifier is only used for rows which are not
unique.EmpIdUniqufier12340415670718Full Text IndexesNot accessed
via normal SELECT statementsRequire use of a
predicate:CONTAINSCONTAINSTABLEFREETEXTFREETEXTTABLECan be used to
search binary values (doc, docx, xls, pdf) stored within the
database.Natural Language SearchCan index XML documents, but only
indexes the values, not the tags.Full Text Indexes (SQL 2005 and
below)Created and managed outside of the database via Microsoft
Search ServiceBacked up with the database (starting in SQL
2005)Searches entire index and returns all matches, which you then
filter against your normal table to return correct set of rows.
Full Text Indexes (SQL 2008 and up)Now stored within the
databaseCommand is still parsed via MS Search service, but looking
is done nativelyFull text search now only searches the required
subset of rowsWhen creating your indexes use an identity field as
the key to improve query performance.XML IndexesAllows you to index
specific nodes of the XML document249 XML Indexes pre tableRequires
a Clustered Index on the tableEach xml column can have a single
primary XML index and multiple secondary XML indexesXML Indexes can
only be created on a single XML ColumnNo online rebuildsNot
available for XML variables. Only used on tables.Primary XML
IndexWhen created creates a hidden node tableContains base table
primary key and 12 columns of info about every node within the XML
valueEffectively the clustered index on the node tableBase Table
Clustered Index ValueNode id from the node tableIncreases storage
200-500%Secondary XML IndexesNon-Clustered Indexes on the hidden
node tableThree kinds of secondary indexesPATH index on the node id
(path) and the valueVALUE index is on the value and the node id
(path)PROPERTY index is on the base tables clustered index, node id
(path) and the valueTodays GoalsIntroduce the different kinds of
indexesCommon Misconceptions about indexesDownsides to
indexesIntroduce advanced index tuning techniquesQ & ACommon
Misconceptions about indexesIndexes dont require maintenanceIf I
create one index for each column in my where clause Ill be fineThe
table is sorted based on the order of the Clustered IndexClustered
Indexes are required
Todays GoalsIntroduce the different kinds of indexesCommon
Misconceptions about indexesDownsides to indexesIntroduce advanced
index tuning techniquesQ & ADownsides to indexesIndexes take up
spaceOn large complex databases the indexes can take up more space
than the tableData is duplicated in each index which contains the
columnIndexes slow down insert, update, delete (especially full
text indexes) statementsUsing the wrong index can be slower than
using no indexEncrypted data cant be effectively indexedTodays
GoalsIntroduce the different kinds of indexesCommon Misconceptions
about indexesDownsides to indexesIntroduce advanced index tuning
techniquesQ & AAdvanced Index Tuning TechniquesFillfactorTells
the SQL Server how much free space to leave in the leaf level
pages.PaddingTells the SQL Server to use the Fillfactor setting to
leave free space in the intermediate-level pages.Online
RebuildsData CompressionWhat is a ColumnStore Index?Totally new and
different approach to indexingData is stored via columns not
rowsEach column is stored separately, then compressed using
VertiPak compression engineSQL Servers first B-Tree less indexHow
does ColumnStore do that?C1C2C3C5C6C4
Existing PagesNeeded ColumnsAs the column store index is scanned
looking for matching values the min and max values are looked at to
see if that row group needs to be scanned at all based on the WHERE
clause of the query.Data is not sortedThere is no such thing as a
key in a column store index
22ColumnStore: Use CaseData continues to grow, but performance
requirements stay the sameMany data warehouses approach PB
rangesData needs to be filtered, aggregated, and grouped despite
the size of the dataset23LimitationsUnsupported Data Types
includeUniqueidentifierBlobNumeric (19,2) or higherRead OnlyOUTER
JOINs using ColumnStore dont perform wellColumn StoreDemo!Using the
Advanced Index Tuning TechniquesCREATE INDEX MyIndex ON
dbo.MyTableON (Col1, Col5, Col3)INCLUDE (Col4, Col2)WHERE Col6 =
Value3WITH (FILLFACTOR=70, PAD_INDEX=ON, ONLINE=ON,
DATA_COMPRESSION = ROW | PAGE);Physical Index B-Tree
LayoutClustered (BOL 2005 / 2008)Non-Clustered (BOL 2005 /
2008)
How large are my indexes?SELECT *FROM
sys.dm_db_index_physical_stats (db_id(), object_id(table_name),
null, null, detailed)Database IdObject IdIndex IdPartition
NumberMode (NULL | Limited, Sampled, Detailed)
What Indexes are being used?DECLARE @dbid INT , @dbName
VARCHAR(100); SELECT @dbid = DB_ID() , @dbName = DB_NAME(); WITH
partitionCTE (OBJECT_ID, index_id, row_count, partition_count)AS(
SELECT [OBJECT_ID] , index_id , SUM([ROWS]) AS 'row_count' ,
COUNT(partition_id) AS 'partition_count' FROM sys.partitions GROUP
BY [OBJECT_ID] , index_id) SELECT OBJECT_NAME(i.[OBJECT_ID]) AS
objectName , i.name , CASE WHEN i.is_unique = 1 THEN 'UNIQUE ' ELSE
'' END + i.type_desc AS 'indexType' , ddius.user_seeks ,
ddius.user_scans , ddius.user_lookups , ddius.user_updates ,
cte.row_count , CASE WHEN partition_count > 1 THEN 'yes' ELSE
'no' END AS 'partitioned?' , CASE WHEN i.type = 2 And i.is_unique =
0 THEN 'Drop Index ' + i.name + ' On ' + @dbName + '.dbo.' +
OBJECT_NAME(ddius.[OBJECT_ID]) + ';' WHEN i.type = 2 And
i.is_unique = 1 THEN 'Alter Table ' + @dbName + '.dbo.' +
OBJECT_NAME(ddius.[OBJECT_ID]) + ' Drop Constraint ' + i.name + ';'
ELSE '' END AS 'SQL_DropStatement'FROM sys.indexes AS iINNER Join
sys.dm_db_index_usage_stats ddius ON i.OBJECT_ID = ddius.OBJECT_ID
And i.index_id = ddius.index_idINNER Join partitionCTE AS cte ON
i.OBJECT_ID = cte.OBJECT_ID And i.index_id = cte.index_idWHERE
ddius.database_id = @dbidORDER BY 1, (ddius.user_seeks +
ddius.user_scans + ddius.user_lookups) ASC , user_updates DESC;
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sqlfool.com (where I stole it from).More
Readinghttp://mrdenny.com/res/table-indexing-netQ & ADenny
[email protected]://itke.techtarget.com/sql-server/http://www.twitter.com/mrdennyPlease
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