DBA_UNDO_EXTENTS

Extents comprising all segments in the system managed undo tablespaces

Columns
   ___________________________
 
   OWNER
      Owner of the segment associated with the extent
   SEGMENT_NAME
      Name of the segment associated with the extent
   TABLESPACE_NAME
      Name of the tablespace containing the extent
   EXTENT_ID
      Extent number in the segment
   FILE_ID
      Name of the file containing the extent
   BLOCK_ID
      Starting block number of the extent
   BYTES
      Size of the extent in bytes
   BLOCKS
      Size of the extent in ORACLE blocks
   RELATIVE_FNO
      Relative number of the file containing the segment header
   COMMIT_JTIME
      Commit Time of the undo in the extent expressed as Julian date
   COMMIT_WTIME
      Commit Time of the undo in the extent expressed as wall clock time
   STATUS
      Transaction Status of the undo in the extent

Related:

Simon Sheppard
SS64.com