Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 
 Home
 E-mail Us
 Oracle Articles
New Oracle Articles


 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog


 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Analysis
 Design
 Implementation
 Oracle Support


 SQL Tuning
 Security

 Oracle UNIX
 Oracle Linux
 Monitoring
 Remote s
upport
 Remote plans
 Remote
services
 Application Server

 Applications
 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S
upport  
 Development  

 Implementation


 Consulting Staff
 Consulting Prices
 Help Wanted!

 


 Oracle Posters
 Oracle Books

 Oracle Scripts
 Ion
 Excel-DB  

Don Burleson Blog 


 

 

 


 

 

 
 

CPU in AWR Report tips

Oracle Tips by Don Burleson

February 20, 2015

Question:  My AWR report is showing CPU as the top entry in the top-5 timed events.

I'm concerned because it is consuming 36% of my total DB Time.

Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                           Avg
                                                          wait   % DB
Event                                 Waits     Time(s)   (ms)   time Wait Class
------------------------------ ------------ ----------- ------ ------ ----------
DB CPU                                            6,452          36.1
log file sync                       391,362       5,015     13   28.0 Commit
SQL*Net message from dblink       2,925,160       1,891      1   10.6 Network
db file scattered read            1,023,422         305      0    1.7 User I/O
read by other session               499,400         213      0    1.2 User I/O


How can I tell from the AWR report if I am experiencing a CPU bottleneck?
 

Answer:  Determining CPU in an AWR report is challenging because you have to look in several areas within the AWR report to get the CPU utilization information.  Just because CPU is the #1 timed foreground event, does not mean that the CPU is pegged at 100%, and it does not necessarily mean that you have a "real:" CPU bottleneck, a case where tasks wait in the runqueue for execution.

See my important notes here on 100% CPU utilization and CPU bottlenecks.

Note: Before we begin discussing CPU utilization metrics within an AWR report, it is important to understand that oracle statistics are incomplete because of incomplete instrumentation on the Oracle database.  However, you can get accurate CPU metrics via vmstat, as well as top and glance.

Using the example AWR report that you have provided, we can determine the total amount of available CPU and see how much total CPU processing time was available.  The first thing we need to note is the total elapsed time for the AWR report, and this is at the very beginning of the AWR REPORT":

WORKLOAD REPOSITORY report for

DB Name         DB Id    Instance     Inst Num Startup Time    Release     RAC
------------ ----------- ------------ -------- --------------- ----------- ---
FINONE        1252548811 mydb              1 13-Dec-12 22:10 11.2.0.3.0  NO

Host Name        Platform                         CPUs Cores Sockets Memory(GB)
---------------- -------------------------------- ---- ----- ------- ----------
MYPROD           AIX-Based Systems (64-bit)         24    12              80.00

              Snap Id      Snap Time      Sessions Curs/Sess
            --------- ------------------- -------- ---------
Begin Snap:     25130 15-Dec-12 03:00:39       425      12.2
  End Snap:     25131 15-Dec-12 04:00:45       430      14.7
   Elapsed:               60.09 (mins)
   DB Time:              298.22 (mins)

Note above the relationship between the "Elapsed" and "DB Time" columns.  The report period was only one hour (60 minutes), yet we see 298 for DB Time.  This suggests that the (298/60) that there were only five session active at any given time.

Now that we know the total time for the report, if we look farther down into the "OPERATING SYSTEM STATISTICS" section on the AWR report, there are three metrics that are important for determining CPU utilization:

  • BUSY_TIME- The total amount of time that the CPU was busy for the elapsed time period.  This will exceed the wall-=clock time because we usually have multiple CPU's.

  • IDLE_TIME - The amount of time that the database was idle.

  • NUM_CPUS - The number of processors available to the Oracle database


    Here is an example AWR report section showing the total CPU usage:

Operating System Statistics        
-> *TIME statistic values are diffed.
   All others display actual values.  End Value is displayed if different
-> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name

Statistic                                  Value        End Value
------------------------- ---------------------- ----------------
. . .
BUSY_TIME                                811,048
IDLE_TIME                              7,854,100
IOWAIT_TIME                              613,785
SYS_TIME                                 153,228
USER_TIME                                657,820
LOAD                                           1                2
OS_CPU_WAIT_TIME                         871,600
RSRC_MGR_CPU_WAIT_TIME                         0
VM_IN_BYTES                       26,080,108,536
VM_OUT_BYTES                      14,015,483,904
PHYSICAL_MEMORY_BYTES             85,899,280,384
NUM_CPUS                                      24
 . . .


Now that we have the salient figures, we can calculate the amount of CPU.  The equation for total available CPU is as follows:

      Available CPU = NUM_CPU's * elapsed_time_bet_snapshots * 60(secs) 

                                =  24 * 60 * 60 = 86,400 seconds

Now we can compare that to the amount of used CPU and see that this database was not CPU-bound.  The used DB CPU (6,452 seconds) was only a small fraction of the total available CPU (86,400 seconds).



References:

- Interpreting CPU Usage in an AWR report - Nikolay Savvinov

 
Get the Complete
Oracle SQL Tuning Information 

The landmark book "Advanced Oracle SQL Tuning  The Definitive Reference"  is filled with valuable information on Oracle SQL Tuning. This book includes scripts and tools to hypercharge Oracle 11g performance and you can buy it for 30% off directly from the publisher.

 

 

Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


                    









Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


 

Copyright © 1996 -  2017

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.

Remote Emergency Support provided by Conversational

 

 

��  
 
 
Oracle Training at Sea
 
 
 
 
oracle dba poster
 

 
Follow us on Twitter 
 
Oracle performance tuning software 
 
Oracle Linux poster