Comments on: Oracle CPU time

By: AWR reports: interpreting CPU usage | Oracle Diagnostician

AWR reports: interpreting CPU usage | Oracle Diagnostician — Tue, 03 Feb 2015 11:17:39 +0000

[…] CPU time represents time spent on CPU and does not include time waiting for CPU. Unfortunately, the latter quantity is not accessible via AWR (but there are indirect ways of extracting in via ASH, see here). […]

By: Kyle Hailey

Kyle Hailey — Wed, 19 Jun 2013 18:19:38 +0000

“WAIT” is wait for non-CPU , non-COMMIT, non-I/O
“WAIT” is other stuff like latches, locks, buffer access etc
wait for CPU is CPU_ORA_WAIT
your database load profile from the data you gave its

CPU_ORA 2.937
CPU_ORA_WAIT 4.913
COMMIT .502
READIO 21.447
WAIT 3.248

if we add all those numbers up we get 33 or so, meaning over that period of time there were 33 session active on average.
Of that 33, there were 21 on average were waiting for I/O, so that’s your BIG bottleneck.
Your next biggest area is CPU wait , CPU_ORA_WAIT, which is almost 5. You shouldn’t be waiting for CPU so that’s a problem. Your machine doesn’t have enough CPU to handle the load.
As far as WAIT and COMMIT goes, they are small compared to your other problems. Don’t worry about them unless a particular session you care about is stuck on those mainly. You can see that by going to the “Top Activity” screen in Enterprise manager (or using a tool like DB Optimizer from Embarcadero)

By: Ajay

Ajay — Wed, 19 Jun 2013 18:02:52 +0000

1 quick question about WAIT=3.248 and COMMIT=.502
I will get into details of wait from db side but in this output, How do I interpret it ? Is it on avg 3.2 sessions are waiting for CPU ? Is there any direct relation of wait number and commit numbers in output with CPU_TOTAL or OS_CPU or any other columns ?
what should do I infer looking at wait and commit numbers in above output

By: Ajay

Ajay — Wed, 19 Jun 2013 14:13:00 +0000

Thanks for your help. I will dig more on cause of wait events.

By: Kyle Hailey

Kyle Hailey — Fri, 14 Jun 2013 21:36:18 +0000

Your CPU demand is greater than your CPU capabilities. You database + OS is demanding 10.3 CPUs on average by your machine only had 8, so you are CPU starved.
What the waits are I don’t know. This article is mainly about CPU.
For wait analysis check out the Top Activity chart in Enterprise Manager
or use DB Optimizer from Embarcadero. The following URL
https://sites.google.com/site/embtdbo/profiler
explains more about waits and load

By: Ajay

Ajay — Fri, 14 Jun 2013 19:19:20 +0000

Thanks for detailed explanation/help along with numbers. Request you few more clarifications
Database is bottlenecked on I/O. – I agree and understand it.
What numbers shows that my system has CPU contention ? If my CPU usage is 68% then why rest of 32% is not used before declaring as CPU contention ?
CPU_ORA_WAIT is 4.913 – why db is not getting cpu even though I have 32% free cpu ?
How do I interpret WAIT=3.248 and COMMIT=.502 ? I mean what does it indicate ?

By: Kyle Hailey

Kyle Hailey — Fri, 14 Jun 2013 03:52:32 +0000

@Ajay :

From your first post

CPU_TOTAL 10.361
CPU_OS 2.511
CPU_ORA 2.937
CPU_ORA_WAIT 4.913
COMMIT .502
READIO 21.447
WAIT 3.248

68% is about 2/3 ( 2/3 = 66.6667 %)
so 2/3 of 8 CPUs is (2*8)/3 = 5.3
the CPU reported is 2.5 for CPU_OS and 2.9 for CPU_ORA making a total of 5.4 which is about 5.3

CPU_OS is CPU used by processes not part of the database you are looking at
CPU_ORA is the CPU being used by the database you are looking at
CPU_ORA_WAIT is the CPU that the database you are looking at wants but isn’t getting

in your stats most of the time is spent waiting on I/O. on average 21 oracle processes are waiting for I/O
Your system has some CPU contention but the database is much more bottlenecked on I/O wait

By: Ajay

Ajay — Thu, 13 Jun 2013 21:43:51 +0000

Small correction in previous post. Its 8 CPU instead of 12

NAME TYPE VALUE
———————————— ———– ——————————
cpu_count integer 8
parallel_threads_per_cpu integer 2
resource_manager_cpu_allocation integer 8

CLASS S
—————- ——-
CPU_ORA_CONSUMED 2.7
CPU_ORA_DEMAND 8.6
CPU_OS 5.0
Commit 0.4
User I/O 18.9
Wait 2.2

Basically I want to know. How much cpu is used by db processes, os processes, waiting on IO and how is the system

By: Ajay

Ajay — Thu, 13 Jun 2013 21:37:52 +0000

This post is very interesting but I could not understand it completely so need your help in interpreting results
I am on 11.2.0.2 HP-UX Itanium with 12 CPU’s
1]
METRIC_NAME VALUE METRIC_UNIT
—————————— ———- ————————-
Host CPU Utilization (%) 68.0972937 % Busy/(Idle+Busy)
CPU Usage Per Sec 293.686119 CentiSeconds Per Second
CPU Usage Per Txn 2.42678109 CentiSeconds Per Txn
Database CPU Time Ratio 9.17658878 % Cpu/DB_Time
Background CPU Usage Per Sec 59.8417409 CentiSeconds Per Second
Host CPU Usage Per Sec 540.916584 CentiSeconds Per Second

2]
CPU_TOTAL CPU_OS CPU_ORA CPU_ORA_WAIT COMMIT READIO WAIT
———- ———- ———- ———— ———- ———- ———-
10.361 2.511 2.937 4.913 .502 21.447 3.248

How Do I co-relate numbers ?
CPU_TOTAL = There are on average 10 sessions running on cpu ?
I did not understand other columns in 2] and how do they corelate to 68% Host CPU utilization
Pls help.

By: vivek

vivek — Sun, 28 Apr 2013 15:24:32 +0000

Hi Chris,

Thanks for the awesome report scripts, i have one query, i want historic CPU usage group by dbusers or osuser, as i have users that fall in different consumer groups.

Your expertise help will really help me.

thanks