Une des taches d’ administration les plus simple que le développeur oublie systématiquement de mettre en place et qui entraîne des pertes de performance importante après plusieurs mois de mise à jour de la base.

Ptit Dje nous fournit un script qui utilise DBCC INDEX DEFRAG et évite de faire chuter les performances de la base lors de l’application. On définit le seuil de fragmentation MAXFRAG à partir de laquelle s’applique la réindexation.

  /*Perform a 'USE <database name>' to select the database in which to run the script.*/
-- Declare variables
SET NOCOUNT ON
DECLARE @tablename VARCHAR (128)
DECLARE @execstr   VARCHAR (255)
DECLARE @objectid  INT
DECLARE @indexid   INT
DECLARE @frag      DECIMAL
DECLARE @maxfrag   DECIMAL   -- Decide on the maximum fragmentation to allow
SELECT @maxfrag = 10.0   -- Declare cursor
DECLARE TABLES CURSOR FOR
   SELECT TABLE_NAME
   FROM INFORMATION_SCHEMA.TABLES
   WHERE TABLE_TYPE = 'BASE TABLE' --and table_name not in ('table_act_entry','table_case')   -- Create the table
CREATE TABLE #fraglist (
   ObjectName CHAR (255),
   ObjectId INT,
   IndexName CHAR (255),
   IndexId INT,
   Lvl INT,
   CountPages INT,
   CountRows INT,
   MinRecSize INT,
   MaxRecSize INT,
   AvgRecSize INT,
   ForRecCount INT,
   Extents INT,
   ExtentSwitches INT,
   AvgFreeBytes INT,
   AvgPageDensity INT,
   ScanDensity DECIMAL,
   BestCount INT,
   ActualCount INT,
   LogicalFrag DECIMAL,
   ExtentFrag DECIMAL)   -- Open the cursor
OPEN TABLES   -- Loop through all the tables in the database
FETCH NEXT
   FROM TABLES
   INTO @tablename   WHILE @@FETCH_STATUS = 0
BEGIN
-- Do the showcontig of all indexes of the table
   INSERT INTO #fraglist
   EXEC ('DBCC SHOWCONTIG (''' + @tablename + ''')
      WITH FAST, TABLERESULTS, ALL_INDEXES, NO_INFOMSGS')
   FETCH NEXT
      FROM TABLES
      INTO @tablename
END   -- Close and deallocate the cursor
CLOSE TABLES
DEALLOCATE TABLES   -- Declare cursor for list of indexes to be defragged
DECLARE indexes CURSOR FOR
   SELECT ObjectName, ObjectId, IndexId, LogicalFrag
   FROM #fraglist
   WHERE LogicalFrag >= @maxfrag
      AND INDEXPROPERTY (ObjectId, IndexName, 'IndexDepth') > 0   -- Open the cursor
OPEN indexes   -- loop through the indexes
FETCH NEXT
   FROM indexes
   INTO @tablename, @objectid, @indexid, @frag   WHILE @@FETCH_STATUS = 0
BEGIN
   PRINT 'Executing DBCC INDEXDEFRAG (0, ' + RTRIM(@tablename) + ',
      ' + RTRIM(@indexid) + ') - fragmentation currently '
       + RTRIM(CONVERT(varchar(15),@frag)) + '%'
   SELECT @execstr = 'DBCC INDEXDEFRAG (0, ' + RTRIM(@objectid) + ',
       ' + RTRIM(@indexid) + ')'
   EXEC (@execstr)       FETCH NEXT
      FROM indexes
      INTO @tablename, @objectid, @indexid, @frag
END   -- Close and deallocate the cursor
CLOSE indexes
DEALLOCATE indexes
DROP TABLE #fraglist
GO

Une solution plus lourde utilisant DBCC Reindex donc entrainant une perte de performance du serveur mais trés efficace car elle recree la totalité des index

USE Mabase
go
DECLARE @TableName varchar(255)
DECLARE TableCursor CURSOR FORSELECT table_name FROM information_schema.tables WHERE table_type = 'base table'
OPEN TableCursor
FETCH NEXT FROM TableCursor INTO @TableName
WHILE @@FETCH_STATUS = 0
BEGIN
DBCC DBREINDEX(@TableName,' ',90)FETCH NEXT FROM TableCursor INTO @TableName
END
CLOSE TableCursor
DEALLOCATE TableCursor
go