  PROMPT Shows users and the rollback segments they are using.
  COL username FORM A10;
  COL machine  FORM A20;
  SELECT username,s.machine,s.osuser,r.name
  FROM v$transaction t, v$rollname r, v$session s
  WHERE t.SES_ADDR = s.SADDR
  AND t.xidusn=r.usn;

