最近闲来无事，正好抽出时间，来总结总结 sql性能优化方面的一下小技巧,小工具。虽然都是些很杂的东西，但是我个人觉得，如果真的清楚了里面的一下指标，或许真的能抵半个DBA。
有些时候，找不到DBA或者根本就没有DBA的时候，程序员就只能靠自己想办法了解决。久而久之，久病成医，说不定就成了半个DBA了。 这里面的一些脚本，有自己总结的，也有网上找的。希望能给程序员在性能优化方面一些帮助。（PS: 这些脚本，都是SQL Server 下的）。
1. 当前连接的Session 有多少
SELECT login_name
,[program_name]
,COUNT(session_id) AS [session_count]
FROM sys.dm_exec_sessions WITH (NOLOCK)
GROUP BY login_name,[program_name]
ORDER BY COUNT(session_id) desc;
2. 每个数据库上的Session 数量是多少
SELECT DB_NAME(dbid) AS DBName
,COUNT(dbid) AS NumberOfConnections
,loginame AS LoginName
FROM sys.sysprocesses
WHERE dbid > 0
GROUP BY dbid,loginame
3. 查看阻塞
SELECT
SPID = er.session_id
,STATUS = ses.STATUS
,[LOGIN] = ses.login_name
,HOST = ses.host_name
,BlkBy = er.blocking_session_id
,DBName = DB_NAME(er.database_id)
,CommandType = er.command
,SQLStatement = st.text
,BlockingText = bst.text
,ObjectName = OBJECT_NAME(st.objectid)
,ElapsedMS = er.total_elapsed_time
,CPUTime = er.cpu_time
,IOReads = er.logical_reads + er.reads
,IOWrites = er.writes
,LastWaitType = er.last_wait_type
,StartTime = er.start_time
,Protocol = con.net_transport
,ConnectionWrites = con.num_writes
,ConnectionReads = con.num_reads
,ClientAddress = con.client_net_address
,Authentication = con.auth_scheme
FROM sys.dm_exec_requests er
OUTER APPLY sys.dm_exec_sql_text(er.sql_handle) st
LEFT JOIN sys.dm_exec_sessions ses
ON ses.session_id = er.session_id
LEFT JOIN sys.dm_exec_connections con
ON con.session_id = ses.session_id
LEFT JOIN sys.dm_exec_requests ber
ON er.blocking_session_id=ber.session_id
OUTER APPLY sys.dm_exec_sql_text(ber.sql_handle) bst
WHERE er.session_id >
ORDER BY er.blocking_session_id DESC,er.session_id
4. 找出哪些表的Index 需要改进
SELECT CONVERT(DECIMAL(, ), 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
5. 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 >
ORDER BY STATS_DATE(i.[object_id], i.index_id) desc;
6. 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 >
ORDER BY ps.avg_fragmentation_in_percent desc;
7. 查询前 10 个可能是性能最差的 SQL 语句
SELECT TOP TEXT AS 'SQL Statement'
,last_execution_time AS 'Last Execution Time'
,(total_logical_reads + total_physical_reads + total_logical_writes) / execution_count AS [Average IO]
,(total_worker_time / execution_count) / 1000000.0 AS [Average CPU Time (sec)]
,(total_elapsed_time / execution_count) / 1000000.0 AS [Average Elapsed Time (sec)]
,execution_count AS "Execution Count"
,qp.query_plan AS "Query Plan"
FROM sys.dm_exec_query_stats qs
CROSS APPLY sys.dm_exec_sql_text(qs.plan_handle) st
CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) qp
ORDER BY total_elapsed_time / execution_count DESC