SQLSERVER排查CPU占用高的情况

怼烎@ 2022-06-07 04:58 234阅读 0赞

今天中午，有朋友叫我帮他看一下数据库，操作系统是Windows2008R2 ,数据库是SQL2008R2 64位

64G内存，16核CPU

硬件配置还是比较高的，他说服务器运行的是金蝶K3软件，数据库实例里有多个数据库

现象

他说是这几天才出现的，而且在每天的某一个时间段才会出现CPU占用高的情况

内存占用不太高，只占用了30个G

CPU占用100%

![12222320-9f57ea80f629472dbd7d8518a911ea5d.jpg][]

![12222412-c505cbb35ff943ec9191dbd44ed0c7db.jpg][]

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排查方向

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

1 USE master
    2 GO
    3 --如果要指定数据库就把注释去掉
    4 SELECT * FROM sys.[sysprocesses] WHERE [spid]>50 --AND DB_NAME([dbid])='gposdb'
    5 SELECT COUNT(*) FROM [sys].[dm_exec_sessions] WHERE [session_id]>50

看一下当前的数据库用户连接有多少

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

![复制代码][copycode.gif]

1 SELECT TOP 10
     2 [session_id],
     3 [request_id],
     4 [start_time] AS '开始时间',
     5 [status] AS '状态',
     6 [command] AS '命令',
     7 dest.[text] AS 'sql语句', 
     8 DB_NAME([database_id]) AS '数据库名',
     9 [blocking_session_id] AS '正在阻塞其他会话的会话ID',
    10 [wait_type] AS '等待资源类型',
    11 [wait_time] AS '等待时间',
    12 [wait_resource] AS '等待的资源',
    13 [reads] AS '物理读次数',
    14 [writes] AS '写次数',
    15 [logical_reads] AS '逻辑读次数',
    16 [row_count] AS '返回结果行数'
    17 FROM sys.[dm_exec_requests] AS der 
    18 CROSS APPLY 
    19 sys.[dm_exec_sql_text](der.[sql_handle]) AS dest 
    20 WHERE [session_id]>50 AND DB_NAME(der.[database_id])='gposdb'  
    21 ORDER BY [cpu_time] DESC

![复制代码][copycode.gif]

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

![复制代码][copycode.gif]

1 --在SSMS里选择以文本格式显示结果
    2 SELECT TOP 10 
    3 dest.[text] AS 'sql语句'
    4 FROM sys.[dm_exec_requests] AS der 
    5 CROSS APPLY 
    6 sys.[dm_exec_sql_text](der.[sql_handle]) AS dest 
    7 WHERE [session_id]>50  
    8 ORDER BY [cpu_time] DESC

![复制代码][copycode.gif]

![12223227-332a5355d78d45a3a4c04113aafce43f.jpg][]

模拟了一些耗CPU时间的动作

![12223307-af7856aed3944453b069559910d70963.jpg][]

![12223318-c112ee2c9312444db3806595ff67a99e.jpg][]

![12223330-8f5a7099919b4608aca3246cc4a885c8.jpg][]

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

1 --查看CPU数和user scheduler数目
    2 SELECT cpu_count,scheduler_count FROM sys.dm_os_sys_info
    3 --查看最大工作线程数
    4 SELECT max_workers_count FROM sys.dm_os_sys_info

查看机器上的所有schedulers包括user 和system  
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

![复制代码][copycode.gif]

1 SELECT
    2 scheduler_address,
    3 scheduler_id,
    4 cpu_id,
    5 status,
    6 current_tasks_count,
    7 current_workers_count,active_workers_count
    8 FROM sys.dm_os_schedulers

![复制代码][copycode.gif]

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

![复制代码][copycode.gif]

1 SELECT TOP 10
     2  [session_id],
     3  [request_id],
     4  [start_time] AS '开始时间',
     5  [status] AS '状态',
     6  [command] AS '命令',
     7  dest.[text] AS 'sql语句', 
     8  DB_NAME([database_id]) AS '数据库名',
     9  [blocking_session_id] AS '正在阻塞其他会话的会话ID',
    10  der.[wait_type] AS '等待资源类型',
    11  [wait_time] AS '等待时间',
    12  [wait_resource] AS '等待的资源',
    13  [dows].[waiting_tasks_count] AS '当前正在进行等待的任务数',
    14  [reads] AS '物理读次数',
    15  [writes] AS '写次数',
    16  [logical_reads] AS '逻辑读次数',
    17  [row_count] AS '返回结果行数'
    18  FROM sys.[dm_exec_requests] AS der 
    19  INNER JOIN [sys].[dm_os_wait_stats] AS dows 
    20  ON der.[wait_type]=[dows].[wait_type]
    21  CROSS APPLY 
    22  sys.[dm_exec_sql_text](der.[sql_handle]) AS dest 
    23  WHERE [session_id]>50  
    24  ORDER BY [cpu_time] DESC

![复制代码][copycode.gif]

比如我当前执行了查询SalesOrderDetail\_test表100次，由于表数据非常多，所以SSMS需要把SQLSERVER执行的结果慢慢的取走，

造成了ASYNC\_NETWORK\_IO等待

1 USE [AdventureWorks]
    2 GO
    3 SELECT * FROM dbo.[SalesOrderDetail_test]
    4 GO 100

![15174130-36875366c8fc4d3aae2b502954ff5dd5.jpg][]

--------------------

问题源头

经过排查和这几天的观察情况，确定是某些表缺失索引导致，现在在这些表上增加了索引，问题解决

![复制代码][copycode.gif]

1 select * from t_AccessControl        --权限控制表权限控制
    2 select * from t_GroupAccess            --用户组权限表用户组权限
    3 select * from t_GroupAccessType        --用户组权限类表用户组权限类
    4 select * from t_ObjectAccess        --对象权限表对象权限
    5 select * from t_ObjectAccessType    --对象权限类型表对象权限类型
    6 select * from t_ObjectType            --对象类型表对象类型

![复制代码][copycode.gif]

查询CPU占用高的语句

![复制代码][copycode.gif]

1 SELECT TOP 10
     2    total_worker_time/execution_count AS avg_cpu_cost, plan_handle,
     3    execution_count,
     4    (SELECT SUBSTRING(text, statement_start_offset/2 + 1,
     5       (CASE WHEN statement_end_offset = -1
     6          THEN LEN(CONVERT(nvarchar(max), text)) * 2
     7          ELSE statement_end_offset
     8       END - statement_start_offset)/2)
     9    FROM sys.dm_exec_sql_text(sql_handle)) AS query_text
    10 FROM sys.dm_exec_query_stats
    11 ORDER BY [avg_cpu_cost] DESC

![复制代码][copycode.gif]

![20094443-153fd769aa054ed88fef36e4ace1cfef.jpg][]

查询缺失索引

![复制代码][copycode.gif]

1 SELECT 
    2     DatabaseName = DB_NAME(database_id)
    3     ,[Number Indexes Missing] = count(*) 
    4 FROM sys.dm_db_missing_index_details
    5 GROUP BY DB_NAME(database_id)
    6 ORDER BY 2 DESC;

![复制代码][copycode.gif]

1 SELECT  TOP 10 
     2         [Total Cost]  = ROUND(avg_total_user_cost * avg_user_impact * (user_seeks + user_scans),0) 
     3         , avg_user_impact
     4         , TableName = statement
     5         , [EqualityUsage] = equality_columns 
     6         , [InequalityUsage] = inequality_columns
     7         , [Include Cloumns] = included_columns
     8 FROM        sys.dm_db_missing_index_groups g 
     9 INNER JOIN    sys.dm_db_missing_index_group_stats s 
    10        ON s.group_handle = g.index_group_handle 
    11 INNER JOIN    sys.dm_db_missing_index_details d 
    12        ON d.index_handle = g.index_handle
    13 ORDER BY [Total Cost] DESC;

![复制代码][copycode.gif]

![20094458-2fb32a30d1d84b8397be4f284eedf319.jpg][]

![20094519-8645c93271b148adbe56687ebb2a3f62.jpg][]

定位问题后，新建非聚集索引

![复制代码][copycode.gif]

1 CREATE NONCLUSTERED INDEX IX_t_AccessControl_F4 ON dbo.t_AccessControl
    2 (
    3     FObjectType
    4 )include([FUserID], [FAccessType], [FAccessMask]) WITH( STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
    5 GO
    6 
    7 drop index IX_t_AccessControl_F4 on t_AccessControl

![复制代码][copycode.gif]

CPU占用恢复正常

![20094716-9a804b97d8fd49f195fd9c459ae68922.jpg][]

跟踪模板和跟踪文件下载，请使用SQL2008R2 版本：[files.cnblogs.com/lyhabc/跟踪模板和trace.rar][files.cnblogs.com_lyhabc_trace.rar]

--------------------

总结

从多次历史经验来看，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。

注意文章开头贴出的客户机器负载情况图

![101217395081429.jpg][]

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