Estimate flashback destination size

Sometimes application team will ask DBA to enable flashback for x number of days. In such case, a DBA needs to estimate the flashback space required for x number of days in order to store the flashback logs. The flashback log size is same as archive log size generated in a database.

Method to estimate flashback space

  • Check the archive generation size via below query
  • Take the average per day size of archives generated
  • Multiply the average archive size with x number of days
  • Ask storage team to add the required space for flashback file system

Check archive log size

Check archive generation size via below query:

select to_char(COMPLETION_TIME,'DD-MON-YYYY') Arch_Date,count(*) No#_Logs,
sum((BLOCKS*512)/1024/1024/1024) Arch_LogSize_GB 
from v$archived_log 
where to_char(COMPLETION_TIME,'DD-MON-YYYY')>=trunc(sysdate-7) and DEST_ID=1
group by to_char(COMPLETION_TIME,'DD-MON-YYYY')
order by to_char(COMPLETION_TIME,'DD-MON-YYYY');

Let us assume the average archive log files size generated per day is 5 GB. Your application team wants you to enable FLASHBACK for 4 days. In this case you will need Approx 20 GB (5GB X 4Days) of space for flashback logs

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