Posted in SQL

OPTIMAL UNDO size

Let’s determine the optimal size for UNDO:

col "ACTUAL UNDO SIZE [MByte]" format 999999
col "UNDO RETENTION [Sec]" format 99999
col "OPTIMAL UNDO RETENTION [Sec]" format 999999
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'
/
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Author:

I am an Oracle DBA with experience in Maximum Availability technology such as RAC, Data Guard, Grid Control and ASM. I worked with version 9i through 12c on a number of operating systems. Next to that I have an extensive experience with PL/SQL, Oracle eBusiness Suite and shell scripting. Specialties: Oracle RAC & ASM (Configuration/Monitoring/Tuning) Oracle Data Guard (Configuration/Monitoring/Tuning) EM12c (Installation / troubleshooting) SQL & PLSQL *nix Shell scripting

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