有关索引的DMV

有关索引的DMV

1.查看那些被大量更新，却很少被使用的索引

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT                                                   
    DB_NAME() AS DatabaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , s.user_updates
    , s.system_seeks + s.system_scans + s.system_lookups
                          AS [System usage]
INTO #TempUnusedIndexes
FROM   sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE 1=2
EXEC sp_MSForEachDB 'USE [?];                          
INSERT INTO #TempUnusedIndexes
SELECT TOP 20
    DB_NAME() AS DatabaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , s.user_updates
    , s.system_seeks + s.system_scans + s.system_lookups
                                         AS [System usage]
FROM   sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE s.database_id = DB_ID()
AND OBJECTPROPERTY(s.[object_id], ''IsMsShipped'') = 0
AND s.user_seeks = 0
    AND s.user_scans = 0
    AND s.user_lookups = 0
AND i.name IS NOT NULL
ORDER BY s.user_updates DESC'                           
SELECT TOP 20 * FROM #TempUnusedIndexes ORDER BY [user_updates] DESC
DROP TABLE #TempUnusedIndexes

 

结果如图:

 

这类索引应该被Drop掉

 

 

最高维护代价的索引

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT                                                    
    DB_NAME() AS DatabaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , (s.user_updates ) AS [update usage]
    , (s.user_seeks + s.user_scans + s.user_lookups) AS [Retrieval usage]
    , (s.user_updates) -
      (s.user_seeks + s.user_scans + s.user_lookups) AS [Maintenance cost]
    , s.system_seeks + s.system_scans + s.system_lookups AS [System usage]
    , s.last_user_seek
    , s.last_user_scan
    , s.last_user_lookup
INTO #TempMaintenanceCost
FROM   sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON  s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE 1=2
EXEC sp_MSForEachDB 'USE [?];                             
INSERT INTO #TempMaintenanceCost
SELECT TOP 20
    DB_NAME() AS DatabaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , (s.user_updates ) AS [update usage]
    , (s.user_seeks + s.user_scans + s.user_lookups)
                    AS [Retrieval usage]
    , (s.user_updates) -
(s.user_seeks + user_scans +
                         s.user_lookups) AS [Maintenance cost]
    , s.system_seeks + s.system_scans + s.system_lookups AS [System usage]
    , s.last_user_seek
    , s.last_user_scan
    , s.last_user_lookup
FROM   sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE s.database_id = DB_ID()
    AND i.name IS NOT NULL
    AND OBJECTPROPERTY(s.[object_id], ''IsMsShipped'') = 0
    AND (s.user_seeks + s.user_scans + s.user_lookups) > 0
ORDER BY [Maintenance cost] DESC'                       
SELECT top 20 * FROM #TempMaintenanceCost ORDER BY [Maintenance cost] DESC
DROP TABLE #TempMaintenanceCost

 

结果如图:

 

Maintenance cost高的应该被Drop掉

 

使用频繁的索引

--使用频繁的索引
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT                                          
    DB_NAME() AS DatabaseName
        , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , (s.user_seeks + s.user_scans + s.user_lookups) AS [Usage]
    , s.user_updates
    , i.fill_factor
INTO #TempUsage
FROM sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE 1=2
EXEC sp_MSForEachDB 'USE [?];                              
INSERT INTO #TempUsage
SELECT TOP 20
    DB_NAME() AS DatabaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , (s.user_seeks + s.user_scans + s.user_lookups) AS [Usage]
    , s.user_updates
    , i.fill_factor
FROM   sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
            AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE s.database_id = DB_ID()
    AND i.name IS NOT NULL
    AND OBJECTPROPERTY(s.[object_id], ''IsMsShipped'') = 0
ORDER BY [Usage] DESC'                                   
SELECT TOP 20 * FROM #TempUsage ORDER BY [Usage] DESC
DROP TABLE #TempUsage

 

结果如图

 

这类索引需要格外注意，不要在优化的时候干掉

 

 

 

碎片最多的索引

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT                                                    
    DB_NAME() AS DatbaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , ROUND(s.avg_fragmentation_in_percent,2) AS [Fragmentation %]
INTO #TempFragmentation
FROM sys.dm_db_index_physical_stats(db_id(),null, null, null, null) s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE 1=2
EXEC sp_MSForEachDB 'USE [?];                               
INSERT INTO #TempFragmentation
SELECT TOP 20
    DB_NAME() AS DatbaseName
    , SCHEMA_NAME(o.Schema_ID) AS SchemaName
    , OBJECT_NAME(s.[object_id]) AS TableName
    , i.name AS IndexName
    , ROUND(s.avg_fragmentation_in_percent,2) AS [Fragmentation %]
FROM sys.dm_db_index_physical_stats(db_id(),null, null, null, null) s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
    AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id   
WHERE s.database_id = DB_ID()
  AND i.name IS NOT NULL
  AND OBJECTPROPERTY(s.[object_id], ''IsMsShipped'') = 0
ORDER BY [Fragmentation %] DESC'                         
SELECT top 20 * FROM #TempFragmentation ORDER BY [Fragmentation %] DESC
DROP TABLE #TempFragmentation

 

结果如下:

 

这类索引需要Rebuild,否则会严重拖累数据库性能

 

自上次SQL Server重启后，找出完全没有使用的索引

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT                                                
    DB_NAME() AS DatbaseName
    , SCHEMA_NAME(O.Schema_ID) AS SchemaName
    , OBJECT_NAME(I.object_id) AS TableName
    , I.name AS IndexName
INTO #TempNeverUsedIndexes
FROM sys.indexes I INNER JOIN sys.objects O ON I.object_id = O.object_id
WHERE 1=2
EXEC sp_MSForEachDB 'USE [?];                          
INSERT INTO #TempNeverUsedIndexes
SELECT
    DB_NAME() AS DatbaseName
    , SCHEMA_NAME(O.Schema_ID) AS SchemaName
    , OBJECT_NAME(I.object_id) AS TableName
    , I.NAME AS IndexName
FROM sys.indexes I INNER JOIN sys.objects O ON I.object_id = O.object_id
LEFT OUTER JOIN sys.dm_db_index_usage_stats S ON S.object_id = I.object_id
        AND I.index_id = S.index_id
        AND DATABASE_ID = DB_ID()
WHERE OBJECTPROPERTY(O.object_id,''IsMsShipped'') = 0
  AND I.name IS NOT NULL
  AND S.object_id IS NULL'
SELECT * FROM #TempNeverUsedIndexes                        
ORDER BY DatbaseName, SchemaName, TableName, IndexName
DROP TABLE #TempNeverUsedIndexes

 

结果如图:

 

这类索引应该小心对待，不能一概而论，要看是什么原因导致这种问题

 

查看索引统计的相关信息

 

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT
    ss.name AS SchemaName
    , st.name AS TableName
    , s.name AS IndexName
    , STATS_DATE(s.id,s.indid) AS 'Statistics Last Updated'
    , s.rowcnt AS 'Row Count'
    , s.rowmodctr AS 'Number Of Changes'
    , CAST((CAST(s.rowmodctr AS DECIMAL(28,8))/CAST(s.rowcnt AS
DECIMAL(28,2)) * 100.0)
                             AS DECIMAL(28,2)) AS '% Rows Changed'
FROM sys.sysindexes s
INNER JOIN sys.tables st ON st.[object_id] = s.[id]
INNER JOIN sys.schemas ss ON ss.[schema_id] = st.[schema_id]
WHERE s.id > 100
  AND s.indid > 0
  AND s.rowcnt >= 500
ORDER BY SchemaName, TableName, IndexName

结果如下:

 

因为查询计划是根据统计信息来的，索引的选择同样取决于统计信息，所以根据统计信息更新的多寡可以看出数据库的大体状况，20%的自动更新对于大表来说非常慢。