Performance Tuning

1) Missing Index

Performance is always associated with Indexes. If your database is missing many indexes, kindly execute the below script to create necessary missing indexes for your database tables. 

SELECT TOP 20

dm_mid.database_id AS DatabaseID,

dm_migs.avg_user_impact*(dm_migs.user_seeks+dm_migs.user_scans) Avg_Estimated_Impact,

dm_migs.last_user_seek AS Last_User_Seek,

OBJECT_NAME(dm_mid.OBJECT_ID,dm_mid.database_id) AS [TableName],

'CREATE INDEX [IX_' + OBJECT_NAME(dm_mid.OBJECT_ID,dm_mid.database_id) + '_'

+ REPLACE(REPLACE(REPLACE(ISNULL(dm_mid.equality_columns,''),', ','_'),'[',''),']','')

+ CASE

WHEN dm_mid.equality_columns IS NOT NULL

AND dm_mid.inequality_columns IS NOT NULL THEN '_'

ELSE ''

END

+ REPLACE(REPLACE(REPLACE(ISNULL(dm_mid.inequality_columns,''),', ','_'),'[',''),']','')

+ ']'

+ ' ON ' + dm_mid.statement

+ ' (' + ISNULL (dm_mid.equality_columns,'')

+ CASE WHEN dm_mid.equality_columns IS NOT NULL AND dm_mid.inequality_columns

IS NOT NULL THEN ',' ELSE

'' END

+ ISNULL (dm_mid.inequality_columns, '')

+ ')'

+ ISNULL (' INCLUDE (' + dm_mid.included_columns + ')', '') AS Create_Statement

FROM sys.dm_db_missing_index_groups dm_mig

INNER JOIN sys.dm_db_missing_index_group_stats dm_migs

ON dm_migs.group_handle = dm_mig.index_group_handle

INNER JOIN sys.dm_db_missing_index_details dm_mid

ON dm_mig.index_handle = dm_mid.index_handle

WHERE dm_mid.database_ID = DB_ID()

ORDER BY Avg_Estimated_Impact DESC




2) Unused Index 

A bad index can hamper the performance

SELECT TOP 25

o.name AS ObjectName

, i.name AS IndexName

, i.index_id AS IndexID

, dm_ius.user_seeks AS UserSeek

, dm_ius.user_scans AS UserScans

, dm_ius.user_lookups AS UserLookups

, dm_ius.user_updates AS UserUpdates

, p.TableRows

, 'DROP INDEX ' + QUOTENAME(i.name)

+ ' ON ' + QUOTENAME(s.name) + '.'

+ QUOTENAME(OBJECT_NAME(dm_ius.OBJECT_ID)) AS 'drop statement'

FROM sys.dm_db_index_usage_stats dm_ius

INNER JOIN sys.indexes i ON i.index_id = dm_ius.index_id

AND dm_ius.OBJECT_ID = i.OBJECT_ID

INNER JOIN sys.objects o ON dm_ius.OBJECT_ID = o.OBJECT_ID

INNER JOIN sys.schemas s ON o.schema_id = s.schema_id

INNER JOIN (SELECT SUM(p.rows) TableRows, p.index_id, p.OBJECT_ID

FROM sys.partitions p GROUP BY p.index_id, p.OBJECT_ID) p

ON p.index_id = dm_ius.index_id AND dm_ius.OBJECT_ID = p.OBJECT_ID

WHERE OBJECTPROPERTY(dm_ius.OBJECT_ID,'IsUserTable') = 1

AND dm_ius.database_id = DB_ID()

AND i.type_desc = 'nonclustered'

AND i.is_primary_key = 0

AND i.is_unique_constraint = 0

ORDER BY (dm_ius.user_seeks + dm_ius.user_scans + dm_ius.user_lookups) ASC




3) Statistics of Whole Database

SQL Server has a logic(500+20% of the table rows are affected) of updating outdated statistics. Two option for this

1. If you have left auto update or auto create statistics on, you should not worry at all, SQL Server will make the task itself.
2. If you have left auto update or auto create statistics off, you should manually update the statistics when it reaches the default of 500+ 20% of table rows.

EXEC sp_updatestats;




4) SQL Wait Statistics

Once SQL Server services have been restarted, manually clear the wait stats

DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR);