什么？有个 SQL 执行了 8 秒！
哪里出了问题？臣妾不知道啊，得找 DBA 啊。
DBA 人呢？离职了！！擦！！！
程序员在无处寻求帮助时，就得想办法自救，努力让自己变成 "伪 DBA"。
索引
找出哪些表的 Index 需要改进
在指定数据库中查找哪些表的 Index 需要改进
根据缓存的查询计划判断 SP 是否需要优化
发现那些 Index 的写远多于读的表
查看 Index 的 Statistics 最后更新时间
查看哪些 Index 被修改的最频繁
查看 Index 碎片化指数
哪个 Index 上的读操作最活跃
哪个 Index 上的写操作最活跃
查看 Index 所使用的 Buffer 数量
按照 IO Latch 等待请求对索引进行排行
找出哪些表的 Index 需要改进
SELECT CONVERT(DECIMAL(18, 2), user_seeks * avg_total_user_cost * (avg_user_impact * 0.01)) AS [index_advantage] ,migs.last_user_seek ,mid.[statement] AS [Database.Schema.Table] ,mid.equality_columns ,mid.inequality_columns ,mid.included_columns ,migs.unique_compiles ,migs.user_seeks ,migs.avg_total_user_cost ,migs.avg_user_impact FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK) INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK) ON migs.group_handle = mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK) ON mig.index_handle = mid.index_handle ORDER BY index_advantage DESC OPTION (RECOMPILE);
这里查询出的数据，只是说明数据寻址时间有点儿长，不一定就是缺少索引所引起的。
在指定数据库中查找哪些表的 Index 需要改进
SELECT DISTINCT CONVERT(DECIMAL(18, 2), user_seeks * avg_total_user_cost * (avg_user_impact * 0.01)) AS [index_advantage] ,migs.last_user_seek ,mid.[statement] AS [Database.Schema.Table] ,mid.equality_columns ,mid.inequality_columns ,mid.included_columns ,migs.unique_compiles ,migs.user_seeks ,migs.avg_total_user_cost ,migs.avg_user_impact ,OBJECT_NAME(mid.[object_id]) AS [Table Name] ,p.rows AS [Table Rows] FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK) INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK) ON migs.group_handle = mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK) ON mig.index_handle = mid.index_handle INNER JOIN sys.partitions AS p WITH (NOLOCK) ON p.[object_id] = mid.[object_id] WHERE mid.database_id = DB_ID() ORDER BY index_advantage DESC OPTION (RECOMPILE);
根据缓存的查询计划判断 SP 是否需要优化
SELECT TOP (25) OBJECT_NAME(objectid) AS [ObjectName] ,query_plan ,cp.objtype ,cp.usecounts FROM sys.dm_exec_cached_plans AS cp WITH (NOLOCK) CROSS APPLY sys.dm_exec_query_plan(cp.plan_handle) AS qp WHERE CAST(query_plan AS NVARCHAR(MAX)) LIKE N'%MissingIndex%' AND dbid = DB_ID() ORDER BY cp.usecounts DESC OPTION (RECOMPILE);
发现那些 Index 的写远多于读的表
SELECT OBJECT_NAME(s.[object_id]) AS [Table Name] ,i.[name] AS [Index Name] ,i.index_id ,i.is_disabled ,i.is_hypothetical ,i.has_filter ,i.fill_factor ,user_updates AS [Total Writes] ,user_seeks + user_scans + user_lookups AS [Total Reads] ,user_updates - (user_seeks + user_scans + user_lookups) AS [Difference] FROM sys.dm_db_index_usage_stats AS s WITH (NOLOCK) INNER JOIN sys.indexes AS i WITH (NOLOCK) ON s.[object_id] = i.[object_id] AND i.index_id = s.index_id WHERE OBJECTPROPERTY(s.[object_id], 'IsUserTable') = 1 AND s.database_id = DB_ID() AND user_updates > (user_seeks + user_scans + user_lookups) AND i.index_id > 1 ORDER BY [Difference] DESC ,[Total Writes] DESC ,[Total Reads] ASC OPTION (RECOMPILE);
由于对索引的写操作远多于读操作，看起来 Index 的帮助不大，但需要根据业务需求来判断是否能够 Drop 掉该索引。
查看 Index 的 Statistics 最后更新时间
SELECT SCHEMA_NAME(o.[schema_id]) + N'.' + o.[name] AS [Object Name] ,o.type_desc AS [Object Type] ,i.[name] AS [Index Name] ,STATS_DATE(i.[object_id], i.index_id) AS [Statistics Date] ,s.auto_created ,s.no_recompute ,s.user_created ,st.row_count ,st.used_page_count FROM sys.objects AS o WITH (NOLOCK) INNER JOIN sys.indexes AS i WITH (NOLOCK) ON o.[object_id] = i.[object_id] INNER JOIN sys.stats AS s WITH (NOLOCK) ON i.[object_id] = s.[object_id] AND i.index_id = s.stats_id INNER JOIN sys.dm_db_partition_stats AS st WITH (NOLOCK) ON o.[object_id] = st.[object_id] AND i.[index_id] = st.[index_id] WHERE o.[type] IN ( 'U' ,'V' ) AND st.row_count > 0 ORDER BY STATS_DATE(i.[object_id], i.index_id) DESC OPTION (RECOMPILE);
查看哪些 Index 被修改的最频繁
SQL Server 2008 R2
SELECT TableName = OBJECT_NAME(s.[object_id]) ,SchemaName = SCHEMA_NAME(o.[schema_id]) ,IndexName = i.[name] ,user_updates ,i.is_primary_key FROM sys.dm_db_index_usage_stats s JOIN sys.objects O ON s.[object_id] = O.[object_id] JOIN sys.indexes i ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id WHERE OBJECTPROPERTY(s.[object_id], 'IsMsShipped') = 0 AND user_seeks = 0 AND user_scans = 0 AND user_lookups = 0 AND i.NAME IS NOT NULL -- Ignore HEAP indexes. ORDER BY user_updates DESC
The user_updates counter indicates the level of maintenance on the index caused by insert, update, or delete operations on the underlying table or view.
SQL Server 2012
SELECT o.[name] AS [Object Name] ,o.[object_id] ,o.type_desc ,s.[name] AS [Statistics Name] ,s.stats_id ,s.no_recompute ,s.auto_created ,sp.modification_counter ,sp.rows ,sp.rows_sampled ,sp.last_updated FROM sys.objects AS o WITH (NOLOCK) INNER JOIN sys.stats AS s WITH (NOLOCK) ON s.object_id = o.object_id CROSS APPLY sys.dm_db_stats_properties(s.object_id, s.stats_id) AS sp WHERE o.type_desc NOT IN ( N'SYSTEM_TABLE' ,N'INTERNAL_TABLE' ) AND sp.modification_counter > 0 ORDER BY sp.modification_counter DESC ,o.[name] OPTION (RECOMPILE);
查看 Index 碎片化指数
SELECT DB_NAME(ps.database_id) AS [Database Name] ,OBJECT_NAME(ps.[object_id]) AS [Object Name] ,i.[name] AS [Index Name] ,ps.index_id ,ps.index_type_desc ,ps.avg_fragmentation_in_percent ,ps.fragment_count ,ps.page_count ,i.fill_factor ,i.has_filter ,i.filter_definition FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, N'LIMITED') AS ps INNER JOIN sys.indexes AS i WITH (NOLOCK) ON ps.[object_id] = i.[object_id] AND ps.index_id = i.index_id WHERE ps.database_id = DB_ID() AND ps.page_count > 2500 ORDER BY ps.avg_fragmentation_in_percent DESC OPTION (RECOMPILE);
哪个 Index 上的读操作最活跃
SELECT OBJECT_NAME(s.[object_id]) AS [ObjectName] ,i.[name] AS [IndexName] ,i.index_id ,user_seeks + user_scans + user_lookups AS [Reads] ,s.user_updates AS [Writes] ,i.type_desc AS [IndexType] ,i.fill_factor AS [FillFactor] ,i.has_filter ,i.filter_definition ,s.last_user_scan ,s.last_user_lookup ,s.last_user_seek FROM sys.dm_db_index_usage_stats AS s WITH (NOLOCK) INNER JOIN sys.indexes AS i WITH (NOLOCK) ON s.[object_id] = i.[object_id] WHERE OBJECTPROPERTY(s.[object_id], 'IsUserTable') = 1 AND i.index_id = s.index_id AND s.database_id = DB_ID() ORDER BY user_seeks + user_scans + user_lookups DESC OPTION (RECOMPILE);
哪个 Index 上的写操作最活跃
SELECT OBJECT_NAME(s.[object_id]) AS [ObjectName] ,i.[name] AS [IndexName] ,i.index_id ,s.user_updates AS [Writes] ,user_seeks + user_scans + user_lookups AS [Reads] ,i.type_desc AS [IndexType] ,i.fill_factor AS [FillFactor] ,i.has_filter ,i.filter_definition ,s.last_system_update ,s.last_user_update FROM sys.dm_db_index_usage_stats AS s WITH (NOLOCK) INNER JOIN sys.indexes AS i WITH (NOLOCK) ON s.[object_id] = i.[object_id] WHERE OBJECTPROPERTY(s.[object_id], 'IsUserTable') = 1 AND i.index_id = s.index_id AND s.database_id = DB_ID() ORDER BY s.user_updates DESC OPTION (RECOMPILE);
查看 Index 所使用的 Buffer 数量
SELECT TOP 25 obj.[name] AS TableName ,i.[name] AS IndexName ,i.[type_desc] AS IndexType ,count(*) AS Buffered_Page_Count ,count(*) * 8192 / (1024 * 1024) AS Buffer_MB ,obj.index_id FROM sys.dm_os_buffer_descriptors AS bd INNER JOIN ( SELECT object_name(object_id) AS NAME ,index_id ,allocation_unit_id ,object_id FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.hobt_id AND ( au.type = 1 OR au.type = 3 ) UNION ALL SELECT object_name(object_id) AS NAME ,index_id ,allocation_unit_id ,object_id FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.hobt_id AND au.type = 2 ) AS obj ON bd.allocation_unit_id = obj.allocation_unit_id LEFT JOIN sys.indexes i ON i.object_id = obj.object_id AND i.index_id = obj.index_id WHERE database_id = db_id() GROUP BY obj.NAME ,obj.index_id ,i.[name] ,i.[type_desc] ORDER BY Buffered_Page_Count DESC
按照 IO Latch 等待请求对索引进行排行
SELECT OBJECT_SCHEMA_NAME(ios.object_id) + '.' + OBJECT_NAME(ios.object_id) AS table_name
,i.[name] AS index_name
,page_io_latch_wait_count
,page_io_latch_wait_in_ms
,CAST(1. * page_io_latch_wait_in_ms / NULLIF(page_io_latch_wait_count, 0) AS DECIMAL(12, 2)) AS page_io_avg_lock_wait_ms
,page_latch_wait_count
,page_latch_wait_in_ms
,CAST(1. * page_latch_wait_in_ms / NULLIF(page_latch_wait_count, 0) AS DECIMAL(12, 2)) AS page_avg_lock_wait_ms
FROM sys.dm_db_index_operational_stats(DB_ID(), NULL, NULL, NULL) ios
INNER JOIN sys.indexes i ON i.object_id = ios.object_id
AND i.index_id = ios.index_id
WHERE OBJECTPROPERTY(ios.object_id, 'IsUserTable') = 1
ORDER BY 3 DESC