UNDO-Tablespace-Usage :: "ACTIVE" vs. "USED"

Question

Hello,
when I run this
SELECT SUM(BYTES)/1024/1024/1024 "GB" ,STATUS
FROM DBA_UNDO_EXTENTS
GROUP BY STATUS;
against my database, I get this
MB STATUS
,008789063 UNEXPIRED
,094177246 EXPIRED
*19,7614746* ACTIVE
But when checking transactions with
SELECT s.sid , s.username , t.used_ublk*8/1024/1024
FROM v$transaction t
, v$session s
WHERE t.ses_addr = s.saddr;
I get this
SID USERNAME T.USED_UBLK*8/1024/1024
109 TRAM_STAT *6,0405426*
Where does this difference come from ???
Regards,
Mynz

Answer 1

ACTIVE: transaction running, still need for rollback
UNEXPIRED: transaction is not running, but still under UNDO_RETENTION period, so still needed.
EXPIRED: transaction is not running, not under UNDO_RETENTION period. When more extents will be needed for active, this extensts will be overwritten.
to check, how many undo are using a session, you can execute:
set pages 100 lines 160
col sid_serial for a20
col orauser for a15
col program for a30
col undoseg for a15
col undo for a10
SELECT TO_CHAR(s.sid)||','||TO_CHAR(s.serial#) sid_serial,
NVL(s.username, 'None') orauser,
s.program,
r.name undoseg,
t.used_ublk * TO_NUMBER(x.value)/1024||'K' "Undo"
FROM sys.v_$rollname r,
sys.v_$session s,
sys.v_$transaction t,
sys.v_$parameter x
WHERE s.taddr = t.addr
AND r.usn = t.xidusn(+)
AND x.name = 'db_block_size';