select * from DBA_SEGMENTS where Segment_Type = 'ROLLBACK' : user_segments « System Tables Data Dictionary « Oracle PL/SQL Tutorial

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2. System Tables Data Dictionary
3. user_segments

SQL>
SQL>
SQL>
SQL> select * from DBA_SEGMENTS
  2   where Segment_Type = 'ROLLBACK';
                                                              

OWNER         SEGMENT_NAME
------------  ---------------------------------------------------------------------------------
PARTITION_NAME                  SEGMENT_TYPE        TABLESPACE_NAME                 HEADER_FILE  HEADER_BLOCK
------------------------------  ------------------  ------------------------------  -----------  ------------
     BYTES      BLOCKS     EXTENTS  INITIAL_EXTENT  NEXT_EXTENT  MIN_EXTENTS  MAX_EXTENTS  PCT_INCREASE   FREELISTS
----------  ----------  ----------  --------------  -----------  -----------  -----------  ------------  ----------
FREELIST_GROUPS  RELATIVE_FNO  BUFFER_
---------------  ------------  -------
SYS           SYSTEM
                                ROLLBACK            SYSTEM                                    1             9
    393216          48           6          114688      1048576            1        32765             0           1
              1             1  DEFAULT

                  
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