Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 8 - RAC Administration

Undo Management in RAC

You may occasionally want to switch to a new undo tablespace for the purpose of executing a large batch process at night. This way, the instance keeps running without any down time. At the time of the switch, the instances maintain control of both the old and new undo tablespaces. The old undo tablespace is marked as ‘pending-offline’ until all the transactions using it are completed.

You can dynamically redirect undo tablespaces by executing the alter system set undo_tablespace statement. For example, assume you have instances RAC1 and RAC2 accessing undo tablespaces undotbs01 and undotbs02 respectively. If you have an idle undo tablespace, for example, undotbs03, you can execute the following statement from either instance to redirect undo processing to undotbs03.

ALTER SYSTEM SET UNDO_TABLESPACE = undotbs3;

The undo tablespace is usually defined when the database is created by using the create DATABASE statement as shown in the following example:

CREATE DATABASE racdb
.
.
UNDO TABLESPACE undotbs_01
DATAFILE '/u01/oracle/rbdb1/undo_01' SIZE 1024M;