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Oracle10g Grid Computing with RAC
Chapter 8 - RAC Administration

System Rollback Segment

The system rollback segment is shared, and is used by all instances for transactions involving system objects. Even when you use the AUM method, Oracle can still use the system rollback segment. There is only one system rollback segment for the entire database. It resides in the SYSTEM tablespace.

Using Rollback Segments - Manual Method

Even though the recommended method is to use AUM, the traditional method of manually creating rollback segments is allowed. In such a case, you need to setup the initialization parameter undo_management=MANUAL. When operating in manual mode, each instance needs at least one rollback segment to start successfully. A rollback segment may be acquired by only one instance. Once an instance acquires a particular rollback segment, it is used exclusively by that instance. No other instance can write to it, although they can read from it for the purpose of read-consistent images.

Public and Private Rollback

Rollback segments can be either public or private. Private rollback segments are used exclusively by an instance. Public rollback segments can be acquired by any of the instances. They are exactly the same in their functionality.

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


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