Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 8 - RAC Administration

Public and Private Rollback

A public rollback segment is created by the PUBLIC clause with the create ROLLBACK SEGMENT command. Any rollback segment created without the PUBLIC clause is considered a private rollback segment. As mentioned, public rollback segments can be acquired by any instance, while private rollback segments are acquired by a specific instance only when the rollback segment's name has been listed in the rollback_segment initialization parameter for the instance, as shown here:

ROLLBACK_SEGMENTS = (RBS10, RBS11, RBS12)

It is preferable to use private rollback segments and they are recommended for ease of administration. When you use private rollback segments, you know which rollback segments are in use by which instance. You are in a position to plan in advance based on the workload for a typical instance. The following example shows how to create a public rollback segment:

create public rollback segment rbseg1
tablespace rbs11 ;