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

  • Check the 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');

  • 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.

Note: Take average size * 30 days to get 1 month flashback space size.