Oracle Flashback

sqlplus / as sysdba
show parameter db_recovery;

sys@EM13REP> show parameter db_recovery;

NAME                                 TYPE        VALUE
==================================== =========== ==============================
db_recovery_file_dest                string      /u07/flashback
db_recovery_file_dest_size           big integer 17G

to change to different directory
sys@EM13REP> alter system set db_recovery_file_dest='/u07/flashback';

to change recovery file size
sys@EM13REP> alter system set db_recovery_file_dest_size='17g';

database is open
sys@EM13REP> alter database flashback on;

ls /u07/flashback

list restore points
SQL> SELECT NAME, SCN, TIME, DATABASE_INCARNATION#, GUARANTEE_FLASHBACK_DATABASE,STORAGE_SIZE FROM V$RESTORE_POINT;

SQL> CREATE RESTORE POINT before_upgrade;

​sys@EM13REP> select flashback_on from v$database;

​
Reference: 
​http://docs.oracle.com/database/122/BRADV/using-flasback-database-restore-points.htm#BRADV71000