Sunday, 21 June 2015

Wait Event "resmgr:cpu quantum"

Wait 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:

1. - UNIX/Linux - vmstat when the runqueue column (r) exceed the cpu_count for the database.

2. - Windows:  When the processor queue length is greater than zero.

If there 100% CPU Utilization then its important to check Processor Queue Length in the system monitor and task manager. In Windows, it's the "Processor Queue Length", and it's displayed in the system monitor and task manager.

Microsoft notes:

"Processor Queue Length (System) This is the instantaneous length of the processor queue in units of threads. All processors use a single queue in which threads wait for processor cycles.

After a processor is available for a thread waiting in the processor queue, the thread can be switched onto a processor for execution. A processor can execute only a single thread at a time. Note that faster CPUs can handle longer queue lengths than slower CPUs."

"The number of threads in the processor queue. Shows ready threads only, not threads that are running. Even multiprocessor computers have a single queue for processor time; thus, for multiprocessors, you need to divide this value by the number of processors servicing the workload. A sustained processor queue of less than two threads per processor is normally acceptable, depending upon the workload."

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