CPU报高，SQLServer如何排查

   

 最近系统在测试过程中，老出现CPU超标情况，有时CPU能够达到90%以上，我的天呢，有点崩溃了，下面一步一步的排查问题吧！

 一般排查都是用下面的脚本，一般会用到三个视图sys.sysprocesses ,dm_exec_sessions ,dm_exec_requests

 看一下当前的数据库用户连接有多少

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">USE masterGO--如果要指定数据库就把注释去掉SELECT * FROM sys.[sysprocesses] WHERE [spid]>50 --AND DB_NAME([dbid])='gposdb'SELECT COUNT(*) FROM [sys].[dm_exec_sessions] WHERE [session_id]>50</span></span></span>

然后使用下面语句看一下各项指标是否正常，是否有阻塞，这个语句选取了前10个最耗CPU时间的会话

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">SELECT TOP 10 [session_id], [request_id], [start_time] AS '开始时间', [status] AS '状态', [command] AS '命令', dest.[text] AS 'sql语句', DB_NAME([database_id]) AS '数据库名', [blocking_session_id] AS '正在阻塞其他会话的会话ID',[wait_type] AS '等待资源类型',[wait_time] AS '等待时间',[wait_resource] AS '等待的资源',[reads] AS '物理读次数',[writes] AS '写次数',[logical_reads] AS '逻辑读次数',[row_count] AS '返回结果行数'FROM sys.[dm_exec_requests] AS der CROSS APPLY sys.[dm_exec_sql_text](der.[sql_handle]) AS dest WHERE [session_id]>50 AND DB_NAME(der.[database_id])='gposdb'  ORDER BY [cpu_time] DESC</span></span></span>

如果想看具体的SQL语句可以执行下面的SQL语句，记得在SSMS里选择以文本格式显示结果

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">--在SSMS里选择以文本格式显示结果SELECT TOP 10 dest.[text] AS 'sql语句'FROM sys.[dm_exec_requests] AS der CROSS APPLY sys.[dm_exec_sql_text](der.[sql_handle]) AS dest WHERE [session_id]>50  ORDER BY [cpu_time] DESC</span></span></span>

还有查看CPU数和user scheduler数和最大工作线程数，检查worker是否用完也可以排查CPU占用情况

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">--查看CPU数和user scheduler数目SELECT cpu_count,scheduler_count FROM sys.dm_os_sys_info--查看最大工作线程数SELECT max_workers_count FROM sys.dm_os_sys_info</span></span></span>

查看机器上的所有schedulers包括user 和system

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;">--查看CPU数和user scheduler数目SELECT cpu_count,scheduler_count FROM sys.dm_os_sys_info--查看最大工作线程数SELECT max_workers_count FROM sys.dm_os_sys_info</span></span>

通过下面语句可以看到worker是否用完，当达到最大线程数的时候就要检查blocking了
对照下面这个表
各种CPU和SQLSERVER版本组合自动配置的最大工作线程数
CPU数   32位计算机      64位计算机
<=4         256                    512
8            288                    576
16           352                    704
32           480                    960

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">SELECTscheduler_address,scheduler_id,cpu_id,status,current_tasks_count,current_workers_count,active_workers_countFROM sys.dm_os_schedulers</span></span></span>

如果SQLSERVER存在要等待的资源，那么执行下面语句就会显示出会话中有多少个worker在等待
结合[sys].[dm_os_wait_stats]视图，如果当前SQLSERVER里面没有任何等待资源，那么下面的SQL语句不会显示任何结果

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">SELECT TOP 10  [session_id],  [request_id],  [start_time] AS '开始时间',  [status] AS '状态',  [command] AS '命令',  dest.[text] AS 'sql语句',  DB_NAME([database_id]) AS '数据库名',  [blocking_session_id] AS '正在阻塞其他会话的会话ID', der.[wait_type] AS '等待资源类型', [wait_time] AS '等待时间', [wait_resource] AS '等待的资源', [dows].[waiting_tasks_count] AS '当前正在进行等待的任务数', [reads] AS '物理读次数', [writes] AS '写次数', [logical_reads] AS '逻辑读次数', [row_count] AS '返回结果行数' FROM sys.[dm_exec_requests] AS der  INNER JOIN [sys].[dm_os_wait_stats] AS dows  ON der.[wait_type]=[dows].[wait_type] CROSS APPLY  sys.[dm_exec_sql_text](der.[sql_handle]) AS dest  WHERE [session_id]>50   ORDER BY [cpu_time] DESC</span></span></span>

查询CPU占用高的语句

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">SELECT TOP 10  total_worker_time/execution_count AS avg_cpu_cost, plan_handle,  execution_count,  (SELECT SUBSTRING(text, statement_start_offset/2 + 1,        (CASE WHEN statement_end_offset = -1           THEN LEN(CONVERT(nvarchar(max), text)) * 2           ELSE statement_end_offset        END - statement_start_offset)/2)     FROM sys.dm_exec_sql_text(sql_handle)) AS query_textFROM sys.dm_exec_query_statsORDER BY [avg_cpu_cost] DESC</span></span></span>

查询缺失索引

<span style="font-family:Comic Sans MS;font-size:18px;"><span style="font-size:18px;"><span style="font-family:Comic Sans MS;font-size:18px;">SELECT     DatabaseName = DB_NAME(database_id)    ,[Number Indexes Missing] = count(*) FROM sys.dm_db_missing_index_detailsGROUP BY DB_NAME(database_id)ORDER BY 2 DESC;SELECT TOP 10[Total Cost] = ROUND(avg_total_user_cost * avg_user_impact * (user_seeks + user_scans),0), avg_user_impact, TableName = statement, [EqualityUsage] = equality_columns, [InequalityUsage] = inequality_columns, [Include Cloumns] = included_columnsFROM sys.dm_db_missing_index_groups gINNER JOIN sys.dm_db_missing_index_group_stats sON s.group_handle = g.index_group_handleINNER JOIN sys.dm_db_missing_index_details dON d.index_handle = g.index_handleORDER BY [Total Cost] DESC;</span></span></span>

一般情况下，如果CPU负载持续很高，但内存和IO都还好的话，这种情况下，首先想到的一定是索引问题，十有八九错不了。