Automate INDEX rebuild based on fragmentation results? - sql

Question

Is it possible to add a maintenance job to check indexes fragmentation. If greater than 50% then rebuild those indexes automatically ?
Index size can vary from 100MB to 10GB.
SQL 2005.
Thank you.

Answer 1

I use this script . Please note I would advise you reading up about the dmv I am using here they are a hidden gem in SQL2005+.
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
CREATE TABLE #FragmentedIndexes
(
DatabaseName SYSNAME
, SchemaName SYSNAME
, TableName SYSNAME
, IndexName SYSNAME
, [Fragmentation%] FLOAT
)
INSERT INTO #FragmentedIndexes
SELECT
DB_NAME(DB_ID()) AS DatabaseName
, ss.name AS SchemaName
, OBJECT_NAME (s.object_id) AS TableName
, i.name AS IndexName
, s.avg_fragmentation_in_percent AS [Fragmentation%]
FROM sys.dm_db_index_physical_stats(db_id(),NULL, NULL, NULL, 'SAMPLED') s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
AND s.index_id = i.index_id
INNER JOIN sys.objects o ON s.object_id = o.object_id
INNER JOIN sys.schemas ss ON ss.[schema_id] = o.[schema_id]
WHERE s.database_id = DB_ID()
AND i.index_id != 0
AND s.record_count > 0
AND o.is_ms_shipped = 0
DECLARE #RebuildIndexesSQL NVARCHAR(MAX)
SET #RebuildIndexesSQL = ''
SELECT
#RebuildIndexesSQL = #RebuildIndexesSQL +
CASE
WHEN [Fragmentation%] > 30
THEN CHAR(10) + 'ALTER INDEX ' + QUOTENAME(IndexName) + ' ON '
+ QUOTENAME(SchemaName) + '.'
+ QUOTENAME(TableName) + ' REBUILD;'
WHEN [Fragmentation%] > 10
THEN CHAR(10) + 'ALTER INDEX ' + QUOTENAME(IndexName) + ' ON '
+ QUOTENAME(SchemaName) + '.'
+ QUOTENAME(TableName) + ' REORGANIZE;'
END
FROM #FragmentedIndexes
WHERE [Fragmentation%] > 10
DECLARE #StartOffset INT
DECLARE #Length INT
SET #StartOffset = 0
SET #Length = 4000
WHILE (#StartOffset < LEN(#RebuildIndexesSQL))
BEGIN
PRINT SUBSTRING(#RebuildIndexesSQL, #StartOffset, #Length)
SET #StartOffset = #StartOffset + #Length
END
PRINT SUBSTRING(#RebuildIndexesSQL, #StartOffset, #Length)
EXECUTE sp_executesql #RebuildIndexesSQL
DROP TABLE #FragmentedIndexes
Also keep in mind that this script can run a while and block access to your tables. Unless you have Enterprise editions SQL can LOCK the table when rebuilding the index. This will block all queries to that table using the index till the index defrag is finished. Thus it is not advised to run index rebuild during operational hours only during maintenance windows. If you are running enterprise edition you can use the ONLINE=ON option to defrag indexes online. This will use more space but your tables wont be blocked/locked during the defrag operation.
Shout if you need more information.
UPDATED:
If you are running this query on a smaller database you can probably use the 'DETAILED' parameter in the call to sys.dm_db_index_physical_stats. This is probably a more detailed examination of the indexes. The discussion in the comments will also point out that on much larger tables it is probably worth doing a SAMPLED scan as this will help reduce the time needed to do the index scan.

Answer 2

In case, you were thinking of avoiding to create any temp tables and parsing the string to create a list of SQL strings. Here is an efficient way of accomplishing it:
USE databasename
GO
DECLARE #Queryresult NVARCHAR(4000)
SET #Queryresult=''
SELECT
#Queryresult=#Queryresult + 'ALTER INDEX ' + QUOTENAME(i.name) + ' ON '
+ QUOTENAME('dbo') + '.'
+ QUOTENAME(OBJECT_NAME(i.OBJECT_ID)) + ' REBUILD;'
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, 'SAMPLED') ss
INNER JOIN sys.indexes i ON i.OBJECT_ID = ss.OBJECT_ID AND i.index_id = ss.index_id
INNER JOIN sys.objects o ON ss.object_id = o.object_id
WHERE ss.avg_fragmentation_in_percent > 50
AND ss.record_count > 0
AND o.is_ms_shipped = 0 --Excludes any objects created as a part of SQL Server installation
AND ss.index_id > 0 --Excludes heap indexes
EXEC sp_executesql #Queryresult

Answer 3

yes, you can.
You can get the fragmented indexes using this query:
SELECT OBJECT_NAME(i.OBJECT_ID) AS TableName,
i.name AS IndexName,
indexstats.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, 'DETAILED') indexstats
INNER JOIN sys.indexes i ON i.OBJECT_ID = indexstats.OBJECT_ID
AND i.index_id = indexstats.index_id
WHERE indexstats.avg_fragmentation_in_percent > 20
and based on the result just build a command to recreate them
I would wrap everything on a Stored Procedure and call it from a SQL Server Job
FYI, 50% is a very big fragmentation. I would go with less.

Answer 4

You can use sys.dm_db_index_physical_stats to get information about your index fragmentation (see the avg_fragmentation_in_percent column). Then you can do an alter index with the rebuild clause whenever your threshold is reached.