Rollback_segments

Type:String
Syntax:ROLLBACK_SEGMENTS =(segment_name [, segment_name] ... )
Modify:No
Range:Any rollback segment names listed in DBA_ROLLBACK_SEGS except
SYSTEM
Basic:Yes
Rac:Multiple instances must have different values.
Notes:ROLLBACK_SEGMENTS allocates one or more rollback segments by name to this instance. If you set this parameter, the instance acquires all of the rollback segments named in this parameter, even if the number of rollback segments exceeds the minimum number required by the instance (calculated as TRANSACTIONS /TRANSACTIONS_PER_ROLLBACK_SEGMENT).
You cannot change the value of this parameter dynamically, but you can change its value and then restart the instance. Although this parameter usually specifies private rollback segments, it can also specify public rollback segments if they are not already in use.To find the name, segment ID number, and status of each rollback segment in the database, query the data dictionary view DBA_ROLLBACK_SEGS.When UNDO_MANAGEMENT is set to AUTO, ROLLBACK_SEGMENTS is ignored.Default value:If you do not specify this parameter, the instance uses public rollback segments by default, unless the UNDO_MANAGEMENT initialization parameter is set to AUTO. In that case, the ROLLBACK_SEGMENTS parameter is ignored and automatic undo management is used.