Download SQL SERVER INDEXES

Managing and Maintaining
Indexes and Statistics
Table Fragmentation Causes
1 Massive Updates or deletes
2 Frequent Page Splitting
3 Disk space contention
4 Insert Statements if Clustered
Key is not a sequential key
How to Check Index
Fragmentation
use AdventureWorks2012
GO
Select
DB_NAME(ips.database_id) DBname,
OBJECT_NAME(ips.object_id) ObjName,
i.name InxName,
ips.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats(db_id(‘AdventureWorks2012'),
default, default, default, default) ips
INNER JOIN sys.indexes i
ON
ips.index_id = i.index_id AND
ips.object_id = i.object_id
WHERE
ips.object_id > 99 AND
ips.avg_fragmentation_in_percent >= 10 AND
ips.index_id > 0
REBUILD OR REORGANIZE?
It is suggested that if fragmentation is between
10% and 30% a Reorganization might be called for
and beneficial. If fragmentation is > 30% most
likely a rebuild is necessary. If fragmentation is <
10%, it probably is not too consequential
Methods to Reorganize an Index
SQL Server Manager allows 3 Methods to Reorganize an Index
1. SQL Server Management Studio (SSMS) – on the fly
2. T-SQL
3. A Maintenance Plan
During Index Reorganization the following
Activities take place
1. Index pages of the index are
compacted
2. The leaf level is reordered to match the
logical order of the leaf nodes in the
index B-tree
Reorganize an Index
T-SQL
USE [AdventureWorks2012]
GO
ALTER INDEX [IX_SalesOrderHeader_OrderDate] on
[Sales].[SalesOrderHeader] REORGANIZE
Always an online operation
Methods to Rebuild an Index
SQL Server Manager allows 2 Methods to Rebuild an Index
1. SQL Server Management Studio (SSMS) – on the fly
2. T-SQL
During Rebuilding an Index the following activities take place
1. Disk space is reclaimed because the pages are compacted
2. The index rows are reordered
3. Fragmentation is removed
Rebuild an Index
T-SQL
USE [AdventureWorks2012]
GO
ALTER INDEX [IX_SalesOrderHeader_OrderDate]
On [Sales].[SalesOrderHeader]
REBUILD WITH (ONLINE = ON) - only with SQL Enterprise 2012
Always an offline operation
How to Check Index Usage
USE AdventureWorks2012
SELECT
DB_NAME(ius.database_id) DBName,
OBJECT_NAME(ius.object_id) ObjName,
i.name,
ius.user_seeks,
ius.user_scans,
ius.user_lookups,
ius.user_updates
FROM sys.dm_db_index_usage_stats ius
INNER JOIN sys.indexes i
ON ius.object_id = i.object_id and
ius.index_id = i.index_id
WHERE
DB_NAME(ius.database_id) = ‘ ‘
‘AdventureWorks2012'
DATABASE STATISTICS
DATABASE STATISTICS are carried both at the Database Level and also
at the Table Level. Typically maintained automatically, they can also be
maintained manually
Database Statistics are updated either thru SSMS or thru T-SQL
UPDATING DATABASE STATISTICS T-SQL
2 Different Programs are available to update Database Statistics
1. UPDATE STATISTICS
2. Sp_updatestats
Here is an example of both programs in use
USE AdventureWorks2012
GO
--Update all statistics within the AdventureWorks2012 database
EXEC sp_updatestats
GO
--update all statistics for a given index on the specified table
UPDATE STATISTICS [Sales].[SalesOrderHeader] [IX_SalesOrderHeader_OrderDate]