Oracle has completely deprecated the use of rollback segments for storing rollback data. It replaced rollbacks with automatic undo management using an undo tablespace. For enabling automatic undo management, you should set the init.ora parameter UNDO_MANAGEMENT to AUTO. You can define any name for undo tablespace by using the UNDO TABLESPACE clause at database-creation time. If the UNDO TABLESPACE clause was omitted during database creation and automatic undo management is enabled, then the database creates a default undo tablespace called SYS_UNDOTBS.