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

 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
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

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

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 







Oracle Top 5 Timed Events

Oracle Tips by Burleson Consulting

AWR Report

Top 5 Timed Events Section

The AWR report provides a super-detailed view of all elapsed-time metrics, and the most important of these metrics is the Top-5 timed events as shown in the output below. This report is critical because it shows those database events that might constitute the bottleneck for the system.



Top 5 Timed Events
~~~~~~~~~~~~~~~~~~                                                     % Total
Event                                               Waits    Time (s) Ela Time
-------------------------------------------- ------------ ----------- --------
db file sequential read                           568,948       4,375    66.15
CPU time                                                        1,983    29.99
db file scattered read                            106,287          65      .99
log file sync                                       7,053          50      .75
log buffer space                                    1,717          47      .71


In the above example, it is clear that this system is waiting on CPU, with 29% of the processing time being spent in the CPU. As a general rule, a server is CPU-bound when the number of processes in the execution queue exceeds the number of CPUs on the server (the r value in rmstat).


The same phenomenon can also be observed in a system which is disk I/O bound. In the AWR sample report section below, one can see that the system is clearly constrained by disk I/O.


Top 5 Timed Events

~~~~~~~~~~~~~~~~~~                                      %

Event                       Waits      Time (s)       Ela


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

db file sequential read           2,598   7,146         48.54

db file scattered read           25,519   3,246         22.04

library cache load lock             673   1,363          9.26

CPU time                                  1,154          7.83

log file parallel write          19,157     837          5.68


Here, reads and writes constitute the majority of the total database time. In this case, we might consider increasing the RAM size of the db_cache_size to reduce disk I/O, tune the SQL to reduce disk I/O, or invest in a faster disk I/O sub-system.


In general, the causes of these top wait events should be investigated in order to minimize database wait time as much as possible. These top wait events are also available in the next report section called Wait Events.



This is an excerpt from my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts:




Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster


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