Printed 2017/08/22 10:23PM

Find missing indexes using SQL Servers index related DMVs

By Basit Aalishan Masood-Al-Farooq, 2013/03/13

Today, we experienced performance issues with few databases that are hosted on one of our most critical production SQL Server. Upon reviewing the query execution plan and querying index related dynamic management views (DMVs), I noticed the problem is related with potential missing indexes on columns. The index related dynamic management views (DMVs) I queried are as follow:

Using these dynamic management views (DMVs), I wrote the following query, which returns the list of possible missing indexes for all SQL Server user databases. The results are ordered by index advantage that helps you to identify how beneficial each index would be, if we create them on the table.

SELECT CAST(SERVERPROPERTY('ServerName') AS [nvarchar](256)) AS [SQLServer],
    db.[database_id] AS [DatabaseID],
    db.[name] AS [DatabaseName],
    id.[object_id] AS [ObjectID],
    id.[statement] AS [FullyQualifiedObjectName],
    id.[equality_columns] AS [EqualityColumns],
    id.[inequality_columns] AS [InEqualityColumns],
    id.[included_columns] AS [IncludedColumns],
    gs.[unique_compiles] AS [UniqueCompiles],
    gs.[user_seeks] AS [UserSeeks],
    gs.[user_scans] AS [UserScans],
    gs.[last_user_seek] AS [LastUserSeekTime],
    gs.[last_user_scan] AS [LastUserScanTime],
    gs.[avg_total_user_cost] AS [AvgTotalUserCost],
    gs.[avg_user_impact] AS [AvgUserImpact],
    gs.[system_seeks] AS [SystemSeeks],
    gs.[system_scans] AS [SystemScans],
    gs.[last_system_seek] AS [LastSystemSeekTime],
    gs.[last_system_scan] AS [LastSystemScanTime],
    gs.[avg_total_system_cost] AS [AvgTotalSystemCost],
    gs.[avg_system_impact] AS [AvgSystemImpact],
    gs.[user_seeks] * gs.[avg_total_user_cost] * (gs.[avg_user_impact] * 0.01) AS [IndexAdvantage],
    'CREATE INDEX [Missing_IXNC_' + OBJECT_NAME(id.[object_id], db.[database_id]) + '_' 
    + REPLACE(REPLACE(REPLACE(ISNULL(id.[equality_columns], ''), ', ', '_'), '[', ''), ']', '') 
    + CASE 
        WHEN id.[equality_columns] IS NOT NULL
            AND id.[inequality_columns] IS NOT NULL
            THEN '_'
        ELSE ''
        END + REPLACE(REPLACE(REPLACE(ISNULL(id.[inequality_columns], ''), ', ', '_'), '[', ''), ']', '') + '_' 
        + LEFT(CAST(NEWID() AS [nvarchar](64)), 5) + ']' + ' ON ' + id.[statement] + ' (' + ISNULL(id.[equality_columns], '') 
        + CASE 
        WHEN id.[equality_columns] IS NOT NULL
            AND id.[inequality_columns] IS NOT NULL
            THEN ','
        ELSE ''
        END + ISNULL(id.[inequality_columns], '') + ')' + ISNULL(' INCLUDE (' + id.[included_columns] + ')', '') AS [ProposedIndex],
    CAST(CURRENT_TIMESTAMP AS [smalldatetime]) AS [CollectionDate]
FROM [sys].[dm_db_missing_index_group_stats] gs WITH (NOLOCK)
INNER JOIN [sys].[dm_db_missing_index_groups] ig WITH (NOLOCK)
    ON gs.[group_handle] = ig.[index_group_handle]
INNER JOIN [sys].[dm_db_missing_index_details] id WITH (NOLOCK)
    ON ig.[index_handle] = id.[index_handle]
INNER JOIN [sys].[databases] db WITH (NOLOCK)
    ON db.[database_id] = id.[database_id]
WHERE id.[database_id] > 4 -- Remove this to see for entire instance
ORDER BY [IndexAdvantage] DESC

Obviously these missing indexes are the ones that the SQL Server optimizer identified during query compilation, and these missing index recommendations are specific recommendation targeting a specific query.  Consider submitting your workload and the proposed index to the Database Tuning Advisor for further evaluation that include partitioning, choice of clustered versus non-clustered index, and so on.

For more information about Database Tuning Advisor, see Start and Use the Database Engine Tuning Advisor and Tutorial: Database Engine Tuning Advisor.

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