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 8 - RAC Administration

UNDO Management

  •  Undo records provide read consistency by maintaining the before image of the data.

  • Multi-version read consistency models require that users always have access to consistent data. Even though many concurrent users access and modify the same set of data blocks, every user has to get consistent data, and data integrity has to be maintained.

  • During database recovery, undo records are used to undo any uncommitted changes applied from the redo log to the data file. Data integrity is maintained even though a failure occurred during active transactions.

  • When the user issues a rollback statement during an active transaction, the undo records are used to undo changes that were made to the database by the uncommitted transaction.

Oracle databases have used rollback segments for a long time. But with release 9i, a new method of undo process was introduced which stores the records in a tablespace. Tablespace-based automatic 'undo' management avoids the tedious management of rollback segments. It is considered a good practice to use the automatic undo method for managing undo segments in Oracle Database 10g. However, we can still use the manual rollback segments as well. Therefore, we have two modes of rollback or undo methods:

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.