Analyze and Fix Index Fragmentation in SQL Server 2008


Create a Clustered Index on FindAndFixFragmentation Table using the below TSQL code
The next step will be to create a clustered index named CL_FindAndFixFragmentation_Index on FindAndFixFragmentation table using the below mentioned TSQL code.

/* Drop the index if it is already existing*/
IF  EXISTS (SELECT * FROM sys.indexes WHERE object_id = OBJECT_ID(N’[dbo].[FindAndFixFragmentation]‘) AND name = N’CL_FindAndFixFragmentation_Index’)
DROP INDEX [CL_FindAndFixFragmentation_Index] ON [dbo].[FindAndFixFragmentation]
GO

/* Create Clustered Index on FindAndFixFragmentation(RowGUID) */
CREATE CLUSTERED INDEX [CL_FindAndFixFragmentation_Index] ON [dbo].[FindAndFixFragmentation]
(
  [RowGUID] ASC
)
WITH (FILLFACTOR = 90) ON [PRIMARY]
GO

You can see that we are creating a clustered index on FindAndFixFragmentation table with a Fill Factor 90. The fill factor option is basically provided for fine tuning index data storage and to improve performance. Whenever an index is created or it is rebuilt, the fill factor value basically determines the percentage of space on each leaf level page that needs to be filled with data. Based on the fill factor value a percentage of free space is allocated on every single page. By default the fill factor value is 0 or 100 which means there will be no free space allocated on each leaf level page. The value for fill factor is defined in percentages and this can be any value in between 1 to 100. In this example the fill factor value provide is 90 which mean on every single page there will be a 10 percentage of free space left to accommodate future growth.

Query to Find Existing Fragmentation on FindAndFixFragmentation Table
Next step will be to execute the below mentioned TSQL query to know the existing fragmentation on FindAndFixFragmentation table. The important values which need to be noted by the database administrators are AvgPageFragmentation and PageCounts. The value for AvgPageFragmentation is 0.341296928327645, which means there is a very little fragmentation existing on the table at this point of time. However the value for PageCounts is 293, which mean the data is stored in that many data pages on SQL Server. This query will be executing many a times in this article.

/* Find index fragmentation */
SELECT
 DB_NAME(DATABASE_ID) AS [DatabaseName],
 OBJECT_NAME(OBJECT_ID) AS TableName,
 SI.NAME AS IndexName,
 INDEX_TYPE_DESC AS IndexType,
 AVG_FRAGMENTATION_IN_PERCENT AS AvgPageFragmentation,
 PAGE_COUNT AS PageCounts
FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL , NULL, N’LIMITED’) DPS
INNER JOIN sysindexes SI
ON DPS.OBJECT_ID = SI.ID AND DPS.INDEX_ID = SI.INDID
GO



Perform Update Operation on FindAndFixFragmentation Table
Next step will be to perform updates on FindAndFixFragmentation table by executing the below mentioned TSQL code. This query will modify all the data for RowGUID column on which we have created clustered index with fill factor as 90.

/* Update all the rows within to FindAndFixFragmentation table create index fragmentation */
USE AnalyzeFragmentation
GO

UPDATE FindAndFixFragmentation
SET RowGUID =NEWID()
GO

Execute the query to find existing fragmentation on FindAndFixFragmentation table as shown in the below snippet.


 
Now you can see that the value for AvgPageFragmentation has changed from 0.341296928327645 to 99.0049751243781, which means index is completely fragmentation. At the same time the value for PageCounts has changed from 293 to 603, which mean more number of data pages are required to store the content. Now the question which comes to your mind is how this can be fixed.

There are two methods to fix index fragmentation issues in SQL Server 2005 and higher versions. The two methods are Reorganize or Rebuild Index. The Reorganize Index is an online operation, however Rebuild Index is not an online operation until you have specified the option ONLINE=ON while performing the Rebuild. Next step will be to perform first REORGANIZE Index option and then finally perform we will perform the REBUILD and see which options is the best.

Continues…

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One Response to “Analyze and Fix Index Fragmentation in SQL Server 2008”

  1. I have fragmented the Indexes even then the fragmentation is there. What is the reason? How to resolve it? How shall i identify all indexes which needs defragmentation? Shall i defragment the indexes which are created for the tables used for replication? If i include the check sys.objects.type_desc=’User Table’ even then the indexes associated with Replication tables are listed there? Also, some tables with name starting with sys are listing. Shall i defragment these sys tables as well?

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