How to check UNDO tablespace usage and who is using more undo

Query To check UNDO tablespace usage:
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set linesize 152
col tablespace_name for a20
col status for a10
select tablespace_name,status,count(extent_id) "Extent Count",
sum(blocks) "Total Blocks",sum(bytes)/(1024*1024*1024) spaceInGB
from   dba_undo_extents
group by  tablespace_name, status having tablespace_name=upper('&TSNAME')
order by tablespace_name;

Query To check who is using more UNDO space:
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SET termout ON
SET heading ON
SET PAGESIZE   6000
SET LINESIZE   200

COLUMN pgm_notes    FORMAT a80        HEADING 'Notes'
COLUMN rbs          FORMAT a16         HEADING 'RBS'             JUST center
COLUMN oracle_user  FORMAT a12        HEADING 'Oracle|Username'
COLUMN sid_serial   FORMAT a12        HEADING 'SID,Serial'
COLUMN unix_pid     FORMAT a6         HEADING 'O/S|PID'
COLUMN Client_User  FORMAT a14        HEADING 'Client|Username'
COLUMN Unix_user    FORMAT a12        HEADING 'O/S|Username'
COLUMN login_time   FORMAT a17        HEADING 'Login Time'
COLUMN last_txn     FORMAT a17        HEADING 'Last Active'
COLUMN undo_kb      FORMAT 999,999,999,999 HEADING 'Undo KB'
COLUMN sql_text     FORMAT a140        HEADING 'Sql Text'


SELECT s.inst_id,
        r.name                   rbs,
        nvl(s.username, 'None')  oracle_user,
        s.osuser                 client_user,
        p.username               unix_user,
        to_char(s.sid)||','||to_char(s.serial#) as sid_serial,
        p.spid                   unix_pid,
        TO_CHAR(s.logon_time, 'mm/dd/yy hh24:mi:ss') as login_time,
        t.used_ublk * 8192  as undo_BYTES,
                st.sql_text as sql_text
   FROM gv$process     p,
        v$rollname     r,
        gv$session     s,
        gv$transaction t,
        gv$sqlarea     st
  WHERE p.inst_id=s.inst_id
    AND p.inst_id=t.inst_id
    AND s.inst_id=st.inst_id
    AND s.taddr = t.addr
    AND s.paddr = p.addr(+)
    AND r.usn   = t.xidusn(+)
    AND s.sql_address = st.address
 --   AND t.used_ublk * 8192 > 10000
  AND t.used_ublk * 8192 > 1073741824
  ORDER
       BY undo_BYTES desc
/