Oracle: X$KTUXE

select
   x.ktuxesta,
   x.ktuxecfl,
   x.ktuxeuel,
   x.ktuxeusn                                          usn,        -- undo segment number
   x.ktuxeslt                                          slt,        -- slot number in transaction table
   x.ktuxesqn                                          wrp,        -- number of times the slot number was used (aka wrap)
   x.ktuxesiz                                          undoblocks, -- remaining number of undo blocks to be applied in rollback
   x.ktuxescnw * power(2,32)+x.ktuxescnb               scn,
   x.ktuxescnw              ,x.ktuxescnb                  ,

  '0x' || to_char(x.ktuxeusn, 'FM0xxxx') || '.' ||
          to_char(x.ktuxeslt, 'FM0xxx' ) || '.' ||
          to_char(x.ktuxesqn, 'FM0xxxxxxxx')           xid ,       -- Transaction ID
   x.ktuxerdbf,
   x.ktuxerdbb,
   u.inst# instid,
   u.name,
   u.status$
from
   x$ktuxe x                          left join
   undo$   u on x.ktuxeusn = u.us#
--where
--  x.ktuxesta = 'ACTIVE' and
--  x.ktuxecfl like '%DEAD%' ;