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Oracle等待事件: resmgr:cpu quantum引发CPU冲高

在上周的活动中,有一位朋友问到一个关于: resmgr:cpu quantum 的问题.这个问题由来已久,也遇到过2次,第一次遇到这个问题,凭直觉就找到了一个隐含参数,通过设置该参数屏蔽了这个问题,未进行进一步研究.

现在再次遇到有人提出,就索性翻翻文档,记录一下.

这个问题显然是和资源管理相关的,如果启用资源管理计划,就可能遇到这个问题.所以常规的解决方案是禁用资源管理,禁用缺省的维护计划(DEFAULT_MAINTENANCE_PLAN Metalink:786346.1)

alter system set resource_manager_plan='';
execute dbms_scheduler.set_attribute('WEEKNIGHT_WINDOW','RESOURCE_PLAN',''); and
execute dbms_scheduler.set_attribute('WEEKEND_WINDOW','RESOURCE_PLAN','');
execute dbms_scheduler.set_attribute('<window name>','RESOURCE_PLAN','');

以上是针对Oracle 11g的一种解决方案.

从以下的Event Class中也可以看到Scheduler的属性:

Top User Events

Event	Event Class	% Activity	Avg Active Sessions
resmgr:cpu quantum	Scheduler	34.69	2.90
CPU + Wait for CPU	CPU	26.62	2.23
latch: library cache	Concurrency	25.91	2.17
latch: shared pool	Concurrency	5.05	0.42
latch free	Other	4.15	0.35

Top Event P1/P2/P3 Values

Event	% Event	P1 Value, P2 Value, P3 Value	% Activity	Parameter 1	Parameter 2	Parameter 3
resmgr:cpu quantum	34.69	"2","0","0"	27.34	location
		"1","0","0"	3.95
		"3","0","0"	3.40
latch: library cache	26.16	"14186265672","214","0"	4.83	address	number	tries
		"14186265512","214","0"	4.43
		"14186266152","214","0"	3.45
latch: shared pool	5.20	"1611577728","213","0"	2.72	address	number	tries
		"1611577568","213","0"	2.31
latch free	4.20	"9464682576","238","0"	1.34	address	number	tries
		"1610749880","205","0"	1.26
		"14251367560","127","0"	1.03

但是很多用户会发现禁用资源计划很多时候没有作用.我第一次遇到这个问题时,第一反应就是直接去寻找是否有隐含参数可以禁用Oracle缺省启用的资源调度,最后通过以下参数设置解决问题:
_resource_manager_always_on = false

在那个案例中,相关的等待事件是: resmgr:active threads,通过隐含参数可以将始终打开的资源计划关闭.

当然还有几个BUG会导致类似的问题,以下是MOS上的相关问题解决方案,提供供参考:
Bug 8221960 WAITS FOR "RESMGR CPU QUANTUM"

One-off patches available Patch 8221960

BUG 7510766 - RESOURCE MANAGER IS OVER THROTTLING

Fixed in 11g Release2 and planned to be included in patchset 10.2.0.5

Bug 7527260 HIGH WAIT EVENTS ON "RESMGR CPU QUANTUM" WHEN RESOURCE MANAGER IS ENABLED   Fixed in patchset 10.2.0.4
Workaround by setting the parameters :

_enable_NUMA_optimization=FALSE
_db_block_numa=1

Bug 6874858 - Poor performance with Resource Manager when RMAN is running

Fixed in 11g Release2 and planned to be included in patchset 10.2.0.5 and 11.1.0.7
Workaround:
     Disable Resource Manager.
One-off patches available Patch 6874858

See also Note 759503.1 Resource Manager Plan Changes Settings Every Week
which might be causing higher waits on 'RESMGR:  ' events due to the changed Resource Plan.

By eygle on 2011-07-21 12:28 | Comments (0) | Case | 2846 |

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