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 master
GO
--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;">SELECT
scheduler_address,scheduler_id,cpu_id,status,current_tasks_count,current_workers_count,active_workers_count
FROM 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],der.[wait_type] AS '等待资源类型',[dows].[waiting_tasks_count] AS '当前正在进行等待的任务数',[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_text
FROM sys.dm_exec_query_stats
ORDER 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_details
GROUP 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_columns
FROM sys.dm_db_missing_index_groups g
INNER JOIN sys.dm_db_missing_index_group_stats s
ON s.group_handle = g.index_group_handle
INNER JOIN sys.dm_db_missing_index_details d
ON d.index_handle = g.index_handle
ORDER 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。

CPU报高，SQLServer如何排查

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