SQL Tuning Scripts

While tuning the SQL database for the project I am working on, I found these scripts by Brent Ozar that were extremely useful. These scripts rely on DMV on your SQL instance - so they are best run after you let your SQL databases run for a while and DMV data got flushed after a reboot. Brent also created videos explaining these scripts. Please note that all these scripts are Brent's creation - not mine.

FIND MISSING INDEXES
In the result, the "impact" column is the indicator how needed the index is. Brent recommends that 10 million or higher number means high - that the index is needed.

/* ------------------------------------------------------------------
-- Title: FindMissingIndexes
-- Author: Brent Ozar
-- Date: 2009-04-01 
-- Modified By: Clayton Kramer ckramer.kramer(at)gmail.com
-- Description: This query returns indexes that SQL Server 2005 
-- (and higher) thinks are missing since the last restart. The 
-- "Impact" column is relative to the time of last restart and how 
-- bad SQL Server needs the index. 10 million+ is high.
-- Changes: Updated to expose full table name. This makes it easier
-- to identify which database needs an index. Modified the 
-- CreateIndexStatement to use the full table path and include the
-- equality/inequality columns for easier identifcation.
------------------------------------------------------------------ */
 
SELECT  
 [Impact] = (avg_total_user_cost * avg_user_impact) * (user_seeks + user_scans),  
 [Table] = [statement],
 [CreateIndexStatement] = 'CREATE NONCLUSTERED INDEX ix_' 
  + sys.objects.name COLLATE DATABASE_DEFAULT 
  + '_' 
  + REPLACE(REPLACE(REPLACE(ISNULL(mid.equality_columns,'')+ISNULL(mid.inequality_columns,''), '[', ''), ']',''), ', ','_')
  + ' ON ' 
  + [statement] 
  + ' ( ' + IsNull(mid.equality_columns, '') 
  + CASE WHEN mid.inequality_columns IS NULL THEN '' ELSE 
   CASE WHEN mid.equality_columns IS NULL THEN '' ELSE ',' END 
  + mid.inequality_columns END + ' ) ' 
  + CASE WHEN mid.included_columns IS NULL THEN '' ELSE 'INCLUDE (' + mid.included_columns + ')' END 
  + ';', 
 mid.equality_columns,
 mid.inequality_columns,
 mid.included_columns
FROM sys.dm_db_missing_index_group_stats AS migs 
 INNER JOIN sys.dm_db_missing_index_groups AS mig ON migs.group_handle = mig.index_group_handle 
 INNER JOIN sys.dm_db_missing_index_details AS mid ON mig.index_handle = mid.index_handle 
 INNER JOIN sys.objects WITH (nolock) ON mid.OBJECT_ID = sys.objects.OBJECT_ID 
WHERE (migs.group_handle IN 
  (SELECT TOP (500) group_handle 
  FROM sys.dm_db_missing_index_group_stats WITH (nolock) 
  ORDER BY (avg_total_user_cost * avg_user_impact) * (user_seeks + user_scans) DESC))  
 AND OBJECTPROPERTY(sys.objects.OBJECT_ID, 'isusertable') = 1 
ORDER BY [Impact] DESC , [CreateIndexStatement] DESC

FIND UNDER USED / UNUSED INDEXES
Since index is mainly used for reading, therefore tables that are written a lot but read rarely may be burdened by indexes. This script is useful for finding those tables. Within the result of this script, the "reads_per_write" is the ratio between the read and write to the table. Depending on the current performance, # of read/write, the index may or may not needed. Generally, Brent recommends to remove indexes where "read_per_write" is below 1.

SELECT 
o.name
, indexname=i.name
, i.index_id   
, reads=user_seeks + user_scans + user_lookups   
, writes =  user_updates   
, rows = (SELECT SUM(p.rows) FROM sys.partitions p WHERE p.index_id = s.index_id AND s.object_id = p.object_id)
, CASE
 WHEN s.user_updates < 1 THEN 100
 ELSE 1.00 * (s.user_seeks + s.user_scans + s.user_lookups) / s.user_updates
  END AS reads_per_write
, 'DROP INDEX ' + QUOTENAME(i.name) 
+ ' ON ' + QUOTENAME(c.name) + '.' + QUOTENAME(OBJECT_NAME(s.object_id)) as 'drop statement'
FROM sys.dm_db_index_usage_stats s  
INNER JOIN sys.indexes i ON i.index_id = s.index_id AND s.object_id = i.object_id   
INNER JOIN sys.objects o on s.object_id = o.object_id
INNER JOIN sys.schemas c on o.schema_id = c.schema_id
WHERE OBJECTPROPERTY(s.object_id,'IsUserTable') = 1
AND s.database_id = DB_ID()   
AND i.type_desc = 'nonclustered'
AND i.is_primary_key = 0
AND i.is_unique_constraint = 0
AND (SELECT SUM(p.rows) FROM sys.partitions p WHERE p.index_id = s.index_id AND s.object_id = p.object_id) > 10000
ORDER BY reads

FIND QUERIES THAT ARE MISSING INDEXES (using Plan Cache)
This is an EXPENSIVE query (not recommended to be run during peak-use-time), running against temporary cached plans.

SELECT qp.query_plan
, total_worker_time/execution_count AS AvgCPU 
, total_elapsed_time/execution_count AS AvgDuration 
, (total_logical_reads+total_physical_reads)/execution_count AS AvgReads 
, execution_count 
, SUBSTRING(st.TEXT, (qs.statement_start_offset/2)+1 , ((CASE qs.statement_end_offset WHEN -1 THEN datalength(st.TEXT) ELSE qs.statement_end_offset END - qs.statement_start_offset)/2) + 1) AS txt 
, qp.query_plan.value('declare default element namespace "http://schemas.microsoft.com/sqlserver/2004/07/showplan"; (/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple/QueryPlan/MissingIndexes/MissingIndexGroup/@Impact)[1]' , 'decimal(18,4)') * execution_count AS TotalImpact
, qp.query_plan.value('declare default element namespace "http://schemas.microsoft.com/sqlserver/2004/07/showplan"; (/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple/QueryPlan/MissingIndexes/MissingIndexGroup/MissingIndex/@Database)[1]' , 'varchar(100)') AS [DATABASE]
, qp.query_plan.value('declare default element namespace "http://schemas.microsoft.com/sqlserver/2004/07/showplan"; (/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple/QueryPlan/MissingIndexes/MissingIndexGroup/MissingIndex/@Table)[1]' , 'varchar(100)') AS [TABLE]
FROM sys.dm_exec_query_stats qs
cross apply sys.dm_exec_sql_text(sql_handle) st
cross apply sys.dm_exec_query_plan(plan_handle) qp
WHERE qp.query_plan.exist('declare default element namespace "http://schemas.microsoft.com/sqlserver/2004/07/showplan";/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple/QueryPlan/MissingIndexes/MissingIndexGroup/MissingIndex[@Database!="m"]') = 1
ORDER BY TotalImpact DESC