Determing the optimal UNDO tablespace size

SELECT d.undo_size/(1024*1024) “ACTUAL UNDO SIZE [MByte]“,        SUBSTR(e.value,1,25) “UNDO RETENTION [Sec]“,        (TO_NUMBER(e.value) * TO_NUMBER(f.value) *        g.undo_block_per_sec) / (1024*1024)       “NEEDED UNDO SIZE [MByte]“   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 […]