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 Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination

SGA - System Global Area

The instance is the structure or entity with which application users connect. The SGA is a group of shared memory structures that contain data and control information for the database instance. Oracle allocates memory for an SGA system whenever the instance is started. Multiple instances can be associated with a database in a RAC system, and each instance has its own SGA. The SGA contains five main areas.

  1. The fixed area.
  2. The variable area.
  3. The database buffer cache.
  4. The log buffer.
  5. The resource directory for a RAC system.
The fixed area of the SGA contains several thousand atomic variables. These are small data structures, such as latches and pointers, which refer to other areas of the SGA. The size of the fixed area is static. It also contains general information about the state of the database and the instance which the background processes need to access.

The variable part of the SGA is made up of a large pool and a shared pool. All memory in the large pool is dynamically allocated, whereas the shared pool contains both dynamically managed memory and a permanent memory. The database buffer cache is where database block copies are held for processing. All user processes concurrently connected to the instance share access to the database buffer cache. There are many groups of buffers within the SGA.

The above text is an excerpt from:

Oracle 10g Grid & Real Application Clusters
Oracle 10g Grid Computing with RAC
ISBN 0-9744355-4-6

by Mike Ault, Madhu Tumma


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 -  2020

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.