text ORCL - UNDO

Posted 2021-04-28

SELECT d.undo_size/(1024*1024) as UNDO_SIZE,
       SUBSTR(e.value,1,25) as UNDO_RETENTION,
       ROUND((d.undo_size / (to_number(f.value) *
       g.undo_block_per_sec))) as OPTIMUM_UNDO_RETENTION
  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';