What do OS stats section of AWR report really tell us?

NUM_LCPUS Probably 0 because LPARs not set up
NUM_VCPUS Same thing
AVG_BUSY_TIME BUSY_TIME/NUM_CPUS
AVG_IDLE_TIME IDLE_TIME/NUM_CPUS
AVG_IOWAIT_TIME IOWAIT_TIME/NUM_CPUS
AVG_SYS_TIME SYS_TIME/NUM_CPUS
AVG_USER_TIME USER_TIME/NUM_CPUS
BUSY_TIME Time equiv of %usr+%sys in sar output
IDLE_TIME Time equiv of %idle in sar
IOWAIT_TIME Time equiv of %wio in sar
SYS_TIME Time equiv of %sys in sar
USER_TIME Time equiv of %usr in sar
LOAD  
OS_CPU_WAIT_TIME Supposedly time waiting on run queues
RSRC_MGR_CPU_WAIT_TIME Time waited coz of resource manager
PHYSICAL_MEMORY_BYTES Total memory in use supposedly
NUM_CPUS Number of CPUs reported by OS
NUM_CPU_CORES Number of CPU sockets on motherboard

 

If you want to convert the times (expressed in seconds) back into percentages, then total elapsed time is
e = BUSY_TIME + IDLE_TIME + IOWAIT TIME or
e = SYS_TIME + USER_TIME + IDLE_TIME + IOWAIT_TIME since BUSY_TIME = (SYS_TIME+USER_TIME)

e should also be roughly close to elapsed time of report (59.78 min * 60 seconds/min * 8 (NUM_CPUS))

but the report itself takes time to run (actually the snapshots take time as well) and neither the snapshot,

the V$ tables the snapshot is taken from, nor the report itself are AS OF a single consistent point in time.

Anyway at this point you can see, (BUSY_TIME / e) = %busy.
Finally,

CPU used by this session                    234,148           65.3         112.4

This is CPU time Oracle reports it used (though we don’t include time spent in SQL*Net code and maybe not all background

processes may be reporting the CPU time they used). It is expressed in centiseconds rather than seconds so

234,148 / (e * 100) will tell you what percent of the total CPU resources on the machine Oracle was keeping busy.

Actually it’s probably easier to look at DB CPU stat since that is already in seconds.

BUSY_TIME – “DB CPU” is the amount of CPU usage that seems to be because of things mostly happening outside the database.

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