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 









Identifying CPU Bottlenecks with vmstat

Oracle Application Server Tips by Burleson Consulting

Waiting CPU resources can be shown in UNIX vmstat command output as the second column under the kthr (kernel thread state change) heading (see Listing 2-1). Tasks may be placed in the wait queue (?b?) if they are waiting on a resource, while other tasks appear in the run queue (?r?) column.

In short, the server is experiencing a CPU bottleneck when ?r? is greater than the number of CPU?s on the server. To see the number of CPUs on the server, you can use one of the following UNIX commands.

Remember that we need to know the number of CPUs on our server because the vmstat runqueue value must never exceed the number of CPUs. A runqueue value of 32 is perfectly acceptable for a 36-CPU server, while a value of 32 would be a serious problem for a 24 CPU server.

In the example below, we run the vmstat utility. For our purposes, we are interested in the first two columns: the run queue ?r?, and the kthr wait ?b? column. In the listing below we see that there are an average of about eight new tasks entering the run queue every five seconds (the ?r? column), while there are five other tasks that are waiting on resources (the ?b? column). Also, a nonzero value in the (?b?) column may indicate a bottleneck.

root> vmstat 5 5

kthr     memory             page              faults        cpu    
----- ----------- ------------------------ ------------ -----------
 r  b   avm    fre  re  pi  po  fr   sr  cy  in     sy  cs  us sy id wa
 7  5 220214   141   0   0   0  42   53   0 1724 12381 2206 19 46 28  7
 9  5 220933   195   0   0   1 216  290   0 1952 46118 2712 27 55 13  5
13  5 220646   452   0   0   1  33   54   0 2130 86185 3014 30 59  8  3
 6  5 220228   672   0   0   0   0    0   0 1929 25068 2485 25 49 16 10

The rule for identifying a server with CPU resource problems is quite simple. Whenever the value of the runqueue ?r? column exceeds the number of CPUs on the server, tasks are forced to wait for execution. There are several solutions to managing CPU overload, and these alternatives are presented in their order of desirability:

1. Add more processors (CPUs) to the server.

2. Load balance the system tasks by rescheduling large batch tasks to execute during off-peak hours.

3. Adjust the dispatching priorities (nice values) of existing tasks.

To understand how dispatching priorities work, we must remember that incoming tasks are placed in the execution queue according to their nice value.  Tasks with a low nice value are scheduled for execution above those tasks with a higher nice value.  Now that we can see when the CPUs are overloaded, let?s look into vmstat further and see how we can tell when the CPUs are running at full capacity.

Identifying High CPU Usage with vmstat

We can also easily detect when we are experiencing a busy CPU on the Oracle database server. Whenever the ?us? (user) column plus the ?sy? (system) column times approach 100%, the CPUs are operating at full capacity .

Please note that it is not uncommon to see the CPU approach 100 percent even when the server is not overwhelmed with work. This is because the UNIX internal dispatchers will always attempt to keep the CPUs as busy as possible. This maximizes task throughput, but it can be misleading for a neophyte.

Remember, it is not a cause for concern when the user + system CPU values approach 100 percent. This just means that the CPUs are working to their full potential. The only metric that identifies a CPU bottleneck is when the run queue (?r? value) exceeds the number of CPUs on the server.

root> vmstat 5 1

kthr     memory             page              faults        cpu    
----- ----------- ------------------------ ------------ -----------
 r  b   avm   fre  re  pi  po  fr   sr  cy  in   sy  cs us sy id wa
 0  0 217485   386  0   0   0   4   14   0 202  300 210 20 75  3  2

The approach of capturing server information along with Oracle information provides the Oracle9iAS administrator with a complete picture of the operation of the system.

Monitoring RAM Memory Consumption

In the UNIX environment, RAM memory is automatically managed by the operating system. In system with ?virtual? memory, a special disk called swap is used to hold chunks of RAM that cannot fit within the available RAM on the server. In this fashion, a virtual memory server can allow tasks to allocate memory above the RAM capacity on the server. As the server is used, the operating system will move some memory pages out to the swap disk in case the server exceeds its physical capacity. This is called a page-out operation. Remember, page-out operations occur even when the database server has not exceeded the RAM capacity.

RAM memory shortages are evidenced by page-in operations. Page-in operations cause Oracle9iAS slowdowns because tasks must wait until their memory region is moved back into RAM from the swap disk. There are several remedies for overloaded RAM memory:

  • Add RAM - Add additional RAM to the server

  • Reduce Oracle9iAS RAM - Reduce the size of the RAM regions by adjusting the parameters for each Oracle9iAS component

Next, let?s move on and take a look at how to build an easy UNIX server monitor by extending the Oracle STATSPACK tables.

Now that we see how to monitor the Oracle9iAS servers, let?s examine how we can use this data to perform server load balancing.

Identifying UNIX Server overload

Once the data is captured in the stats$vmstat table, there is a wealth of reports that can be generated. Because all of the server statistics exist inside a single Oracle table, it is quite easy to write SQL*Plus queries to extract the data.

The vmstat data can be used to generate all types of interesting reports. There are four classes of vmstat reports:

  • Exception reports - These reports show the time period where predefined thresholds are exceeded.

  • Daily trend reports - These reports are often run and used with Excel spreadsheets to produce trending graphs.

  • Hourly trend reports - These reports show the average utilization, averaged by the hour of the day. These reports are very useful for showing peak usage periods in a production environment.

  • Long-term predictive reports - These reports generate a long-term trend line for performance. The data from these reports is often used with a linear regression to predict when additional RAM memory or CPU power is required for the server.

Let?s now examine the script that can be used to generate these server reports and see how this information can help us tune our Oracle database.

This is an excerpt from "Oracle 10g Application Server Administration Handbook" by Don Burleson and John Garmany.

If you like Oracle tuning, you may enjoy the new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

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