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。