Get optimized undo_retention size for Oracle

reference:

https://www.akadia.com/services/ora_optimize_undo.html#:~:text=Turning%20on%20automatic%20undo%20management,tablespace%20and%20set%20UNDO_MANAGEMENT%20%3D%20AUTO.&text=You%20can%20choose%20to%20allocate,size%20and%20the%20database%20activity.

 

https://ittutorial.org/determining-the-optimal-oracle-undo-retention-period/

 

 

Calculate UNDO_RETENTION  for given UNDO Tabespace

 

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'；

 

Calculate Needed UNDO Size for given Database Activity

 

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 = 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'