resmgr:cpu quantum

resmgr:cpu quantum

Lots of session waiting on event “resmgr:cpu quantum”.

The wait event resmgr:cpu quantum is a normal wait event used by the Oracle Resource Manager to control CPU distribution.   The resmgr:cpu quantum only occurs when the resource manager is enabled and the resource manage is "throttling" CPU consumption.

You can also detect an overloaded CPU when you see the “resmgr:cpu quantum” event in a top-5 timed event on a AWR or STATSPACK report.

The "resmgr:cpu quantum" only applies when the Oracle resource manager is deployed, and there are other ways to detect an overloaded CPU:

From AWR

“resmgr:cpu quantum” means a session is waiting in a resource queue, wait until resource manager assign CPU pieces to it.

Resource manager is not enabled in this DB:

SQL> show parameter resource
NAME                          TYPE                 VALUE
----------------------------- -------------------- ------------
resource_manager_plan         string               NIGHT_BATCH_PROC

But we know by default there is a maintenance task defined for database

DEFAULT_MAINTENANCE_PLAN and there are windows defined for the maintenance task and there are resource plan defined for the windows.

Timed Foreground Events:

Event                Waits      Time(s)   Avg wait(ms) % DB time Wait Class

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

resmgr:cpu quantum   3,241,596  3,546,421       216968     99.48  Scheduler

CAUSE

This is due to DEFAULT_MAINTENANCE_PLAN. From 11g onwards every weekday window has a pre-defined Resource Plan called DEFAULT_MAINTENANCE_PLAN, which will become active once the related window opens. In 10gR2, DEFAULT_MAINTENANCE_PLAN is associated with WEEKNIGHT_WINDOW and WEEKEND_WINDOW.

Following entries can also be noted in alert log at the time of issue.

Thu Nov 21 23:30:40 2015

Clearing Resource Manager plan via parameter

….

Thu Nov 21 23:30:40 2015

Setting Resource Manager plan SCHEDULER[0x2C55]:DEFAULT_MAINTENANCE_PLAN via scheduler window

Setting Resource Manager plan DEFAULT_MAINTENANCE_PLAN via parameter

Thu Nov 21 23:30:40 2015

Begin automatic SQL Tuning Advisor run for special tuning task "SYS_AUTO_SQL_TUNING_TASK"

SOLUTION

Support Note :

Note 392037.1 - Database 'Hangs'. Sessions Wait for 'resmgr:cpu quantum'

Note 1339803.1   Recommended Patches for CPU Resource Manager

Set the maintenance window to other time where CPU resource is available maximum

During peak time clear the resource_manager_plan to none

alter system set resource_manager_plan='' scope=both;

References

High "Resmgr:Cpu Quantum" Wait Events In 11g Even When Resource Manager Is Disabled [ID 949033.1]
Resource Manager and Sql Tunning Advisory DEFAULT_MAINTENANCE_PLAN [ID 786346.1]