Monday 1 November 2010

SQL: Cleaning Up After the Database Tuning Engine Advisor

I’ve recently had to do a quick bit of DB performance analysis work on a 3rd Party database to see if I can improve performance(without being too invasive).  The quickest way to do this, is using the Database Tuning Engine Advisor tool that comes with SQL 2008 (the best way is to have loads of experience and a tonne of time to properly analyse the database).

Part of my analysis procedure was to make a script of queries that I could run with and without the DTA recommended indexes to evaluate any real world improvement.  This meant I needed to be able to roll back any indexes created by DTA.  Unfortunately, DTA gives you and install script for the new indexes but not a removal script.  I needed to write something myself.

Fortunately, the DTA created indexes and statistics are all prefixed with _dta_ so it’s relatively easy to write a query to remove the automatically created scripts:

First to drop the generated statistics:

   1: DECLARE @dtaStats AS TABLE(Id INT IDENTITY(1,1), StatName VARCHAR(255), TableName VARCHAR(255))
   2: DECLARE @currentId AS INT
   3: DECLARE @lastId AS INT
   4:  
   5: DECLARE @statName VARCHAR(255)
   6: DECLARE @tableName VARCHAR(255)
   7:  
   8: INSERT INTO @dtaStats(StatName,TableName)
   9:     SELECT name, OBJECT_NAME(OBJECT_ID) AS TABLENAME
  10:     FROM sys.stats
  11:     WHERE name like '_dta_stat_%'
  12:  
  13: SET @currentId=NULL
  14: SET @lastId=0
  15:  
  16: SELECT @currentId=MIN(Id)
  17: FROM @dtaStats 
  18: WHERE Id>@LastId
  19:  
  20: WHILE (@currentId IS NOT NULL)
  21: BEGIN
  22:  
  23:     SELECT @statName=StatName, @tableName=TableName FROM @dtaStats WHERE Id=@currentId
  24:     
  25:     PRINT 'DROP STATISTICS ' + @tableName + '.' + @statName
  26:     
  27:     EXEC('DROP STATISTICS ' + @tableName + '.' + @statName)
  28:     
  29:     SET @lastId = @currentId 
  30:     SET @currentId=null
  31:  
  32:     SELECT @currentId=MIN(Id)
  33:     FROM @dtaStats 
  34:     WHERE Id>@LastId
  35:  
  36: END
  37:  
  38:  

Then drop the generated indexes:

   1:  
   2: DECLARE @dtaIndex AS TABLE(Id INT IDENTITY(1,1), IndexName VARCHAR(255), TableName VARCHAR(255))
   3: DECLARE @currentId AS INT
   4: DECLARE @lastId AS INT
   5:  
   6: DECLARE @IndexName VARCHAR(255)
   7: DECLARE @tableName VARCHAR(255)
   8:  
   9: INSERT INTO @dtaIndex(IndexName,TableName)
  10:     SELECT name, OBJECT_NAME(OBJECT_ID) AS TABLENAME
  11:     FROM sys.indexes
  12:     WHERE name like '_dta_index_%'
  13:     
  14: SET @lastId=0
  15: SET @currentId=NULL
  16:  
  17: SELECT @currentId=MIN(Id)
  18: FROM @dtaIndex 
  19: WHERE Id>@LastId
  20:  
  21: PRINT @currentId
  22:  
  23: WHILE (@currentId IS NOT NULL)
  24: BEGIN
  25:  
  26:     SELECT @IndexName=IndexName, @tableName=TableName FROM @dtaIndex WHERE Id=@currentId
  27:     
  28:     PRINT 'DROP INDEX ' + @IndexName + ' ON ' + @tableName
  29:     
  30:     EXEC('DROP INDEX ' + @IndexName + ' ON ' + @tableName)
  31:     
  32:     SET @lastId = @currentId 
  33:     SET @currentId=NULL
  34:  
  35:     SELECT @currentId=MIN(Id)
  36:     FROM @dtaIndex 
  37:     WHERE Id>@LastId
  38:  
  39: END
  40:  
  41:  

The database is now back to a pre-DTA’ed state!

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