UNDO tablespace size checks

# undo size check #
---------------------------
//

SELECT d.undo_size/(1024*1024) "ACTUAL UNDO SIZE [MByte]",
SUBSTR(e.value,1,25) "UNDO RETENTION [Sec]",
ROUND((d.undo_size / (to_number(f.value) *
g.undo_block_per_sec))) "OPTIMAL UNDO RETENTION [Sec]"
FROM ( SELECT SUM(a.bytes) undo_size
FROM v$datafile a,
v$tablespace b,
dba_tablespaces c
WHERE c.contents = 'UNDO'
AND c.status = 'ONLINE'
AND b.name = c.tablespace_name
AND a.ts# = b.ts#
) d,
v$parameter e,
v$parameter f,
( SELECT MAX(undoblks/((end_time-begin_time)*3600*24))
undo_block_per_sec
FROM v$undostat
) g
WHERE e.name = 'undo_retention'
AND f.name = 'db_block_size';

//

SELECT MAX(undoblks/((end_time-begin_time)*3600*24))"UNDO_BLOCK_PER_SEC"FROM v$undostat;

//

# Which user using how much UNDO #
-------------------------------------------
//

select s.sid,
       s.username,
       sum(ss.value) / 1024 / 1024 as undo_size_mb
from  v$sesstat ss
  join v$session s on s.sid = ss.sid
  join v$statname stat on stat.statistic# = ss.statistic#
where stat.name = 'undo change vector size'
and s.type <> 'BACKGROUND'
and s.username IS NOT NULL
group by s.sid, s.username;

//