High CPU Usage 原因及分析

常见的高CPU利用率出现几个原因：

1. Missing Index
2. 统计信息过时
3. 非SARG查询
4. Implicit Conversions
5. Parameter Sniffing
6. Non-parameter Ad-hoc Query
7. 非必要并行查询

--1.Check the Architecture's Type is or not NUMA (non-uniform memory access)

select

scheduler_id,

cpu_id,

parent_node_id,

status

from sys.dm_os_schedulers;

--2. The memory size of memory clerks. Checking the Buffer Pool Memory(MEMORYCLERK_SQLBUFFERPOOL) size and SQL Queuery Plan(MEMORYCLERK_SQLQUERYPLAN) is very important for tuning the performance.

select

type,

memory_node_id,

virtual_memory_committed_kb,

virtual_memory_reserved_kb,

awe_allocated_kb

from sys.dm_os_memory_clerks

order by virtual_memory_reserved_kb desc;

--3. Check the Size of Current Cache Plan.

select

objtype ,

COUNT(*) AS 'Number of Plans' ,

SUM(CAST(size_in_bytes AS BIGINT)) / 1024 / 1024 AS 'Plan Cache Size (MB)'

FROM sys.dm_exec_cached_plans

Group by objtype;

--4. Check the Type of CPU of SQL Server

select

cpu_count as 'Logical CUP Count',

hyperthread_ratio as 'Hyperthread Radio',

cpu_count /hyperthread_ratio as 'Physical CPU Count',

physical_memory_in_bytes/1048576 as 'Physical Memory (MB)'

from sys.dm_os_sys_info

--5.Check the IO of Datafile or Logfiles.

SELECT DB_NAME(DB_ID()) AS [Database Name] ,

[file_id] ,

num_of_reads ,

num_of_writes ,

num_of_bytes_read ,

num_of_bytes_written ,

CAST(100. * num_of_reads / ( num_of_reads + num_of_writes ) AS DECIMAL(10,

1)) AS [# Reads Pct] ,

CAST(100. * num_of_writes / ( num_of_reads + num_of_writes ) AS DECIMAL(10,

1)) AS [# Write Pct] ,

CAST(100. * num_of_bytes_read / ( num_of_bytes_read

+ num_of_bytes_written ) AS DECIMAL(10,

1)) AS [Read Bytes Pct] ,

CAST(100. * num_of_bytes_written / ( num_of_bytes_read

+ num_of_bytes_written ) AS DECIMAL(10,

1)) AS [Written Bytes Pct]

FROM sys.dm_io_virtual_file_stats(DB_ID(), NULL);

--6. Check the top 10 longest waits

SELECT TOP ( 10 )

wait_type ,

waiting_tasks_count ,

( wait_time_ms - signal_wait_time_ms ) AS resource_wait_time ,

max_wait_time_ms ,

CASE waiting_tasks_count

WHEN 0 THEN 0

ELSE wait_time_ms / waiting_tasks_count

END AS avg_wait_time

FROM sys.dm_os_wait_stats

WHERE wait_type NOT LIKE '%SLEEP%' -- È¥³ý²»Ïà¹ØµÄµÈ´ýÀàÐÍ

AND wait_type NOT LIKE 'XE%'

AND wait_type NOT IN -- È¥³ýϵͳÀàÐÍ

( 'KSOURCE_WAKEUP', 'BROKER_TASK_STOP', 'FT_IFTS_SCHEDULER_IDLE_WAIT',

'SQLTRACE_BUFFER_FLUSH', 'CLR_AUTO_EVENT', 'BROKER_EVENTHANDLER',

'BAD_PAGE_PROCESS', 'BROKER_TRANSMITTER', 'CHECKPOINT_QUEUE',

'DBMIRROR_EVENTS_QUEUE', 'SQLTRACE_BUFFER_FLUSH', 'CLR_MANUAL_EVENT',

'ONDEMAND_TASK_QUEUE', 'REQUEST_FOR_DEADLOCK_SEARCH', 'LOGMGR_QUEUE',

'BROKER_RECEIVE_WAITFOR', 'PREEMPTIVE_OS_GETPROCADDRESS',

'PREEMPTIVE_OS_AUTHENTICATIONOPS', 'BROKER_TO_FLUSH' )

ORDER BY wait_time_ms DESC

--7.Check the parallelism Query

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

WITH XMLNAMESPACES

(DEFAULT 'http://schemas.microsoft.com/SQL Server/2004/07/showplan')

SELECT query_plan AS CompleteQueryPlan ,

n.value('(@StatementText)[1]', 'VARCHAR(4000)') AS StatementText ,

n.value('(@StatementOptmLevel)[1]', 'VARCHAR(25)')

AS StatementOptimizationLevel ,

n.value('(@StatementSubTreeCost)[1]', 'VARCHAR(128)')

AS StatementSubTreeCost ,

n.query('.') AS ParallelSubTreeXML ,

ecp.usecounts ,

ecp.size_in_bytes

FROM sys.dm_exec_cached_plans AS ecp

CROSS APPLY sys.dm_exec_query_plan(plan_handle) AS eqp CROSS APPLY query_plan.nodes

('/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple')

AS qn ( n )

WHERE n.query('.').exist('//RelOp[@PhysicalOp="Parallelism"]') = 1