[Oracle DataBase Server 12.1 installation on Windows 2008 Server]: Enable FLASH BACK mode


FlashBack could help if you need to restore changes or look previous values of record in the database. With this option server needs additional resources, because it should store additional information in the database.

sqlplus / as sysdba


SQL> shutdown immediate;
SQL> startup mount exclusive;
SQL> alter database flashback on;
SQL> alter database open;


SQL> select flashback_on from v$database;


FLASHBACK_ON
------------------
YES

UNDO_RETENTION - (when server works in Flash Back mode) this parameter is setup minimum time in seconds what server should store data for undo changes. Data for undo will store in the UNDO_TABLESPACE and you should provide enough space in this tablespace.

Setup parameter UNDO_RETENTION equal 30 minutes

SQL> alter system set UNDO_RETENTION = 1800;
SQL> alter tablespace UNDO RETENTION GUARANTEE;


SQL> show parameter UNDO_RETENTION


NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_retention                       integer     1800


SQL> quit