Enable or Disable Flashback Mode in Oracle11g Database

Enable Flashback Mode 

Step 1:- Log on to the database and check archivelog mode for database. Its mandatory that database must have enabled archivelog mode 

[oracle@pract1 fra]$ sqlplus "/ as sysdba"

SQL*Plus: Release 11.2.0.1.0 Production on Thu Jul 28 18:03:43 2016

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select instance_name, status from v$instance;

INSTANCE_NAME    STATUS
---------------- ------------
KMDB             OPEN

SQL> archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /u01/app/oracle/product/11.2.0/dbhome_1/dbs/arch
Oldest online log sequence     1
Current log sequence           2

Step 2:- Looks like archivelog destination parameter is set to default location. We will change the archivelog destination to new location 

SQL> alter system set log_archive_dest_1='LOCATION=/u01/oradata/KMDB/arch' scope = both;

System altered.

Step 3:- Verify the archivelog destination which is pointing to new location

SQL> archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /u01/oradata/KMDB/arch
Oldest online log sequence     1
Current log sequence           2

Step 4:- Shutdown the database and start it in mount state

SQL> shu immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> startup mount
ORACLE instance started.

Total System Global Area  839282688 bytes
Fixed Size                  2217992 bytes
Variable Size             494929912 bytes
Database Buffers          339738624 bytes
Redo Buffers                2396160 bytes
Database mounted.

Step 5:- We need to set archivelog mode and open the database

SQL> alter database archivelog;

Database altered.

SQL> alter database open;

Database altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /u01/oradata/KMDB/arch
Oldest online log sequence     1
Next log sequence to archive   2
Current log sequence           2

Step 6:- Check the flashback mode and flash recovery area parameter for the database

SQL> select name,  flashback_on from v$database;

NAME      FLASHBACK_ON
--------- ------------------
KMDB      NO

SQL> sho parameter recovery

NAME                                 TYPE        VALUE
------------------------------------ ----------- --------------
db_recovery_file_dest                string
db_recovery_file_dest_size           big integer 0
recovery_parallelism                 integer     0

Step 7:- Now we will set the flash recovery area parameter

SQL> alter system set db_recovery_file_dest_size=2g scope = both;

System altered.

SQL> alter system set db_recovery_file_dest='/u01/oradata/KMDB/fra' scope = both;

System altered.

Step 8:- Enable flashback mode and verify if its enabled

SQL> alter database flashback on;

Database altered.

SQL> select name,  flashback_on from v$database;

NAME      FLASHBACK_ON
--------- ------------------
KMDB      YES

Disable Flashback Mode

Step 1:- Disable the flashback mode using below mentioned command and verify the status

SQL> alter database flashback off;

Database altered.

SQL> select name,  flashback_on from v$database;

NAME      FLASHBACK_ON

--------- ------------------

KMDB      NO

Possible Errors during Activity 

ORA-38706: Cannot turn on FLASHBACK DATABASE logging.

ORA-38707: Media recovery is not enabled.

ORA-02097: parameter cannot be modified because specified value is invalid

ORA-19802: cannot use DB_RECOVERY_FILE_DEST without DB_RECOVERY_FILE_DEST_SIZE

ORA-01126: database must be mounted in this instance and not open in any

instance

Case 1:- Archivelog not enabled

SQL> alter database flashback on;

alter database flashback on

*

ERROR at line 1:

ORA-38706: Cannot turn on FLASHBACK DATABASE logging.

ORA-38707: Media recovery is not enabled.

Cause:- 

This error occurs when we try to enable the flashback mode without enabling archivelog mode 

Solution:- 

After the enabling the archivelog mode, issue should be resolved. Click Here on How to enable archivelog mode

Case 2:- DB_RECOVERY_FILE_DEST parameter no set in database parameter file

SQL> alter system set db_recovery_file_dest='/u01/oradata/KMDB/fra' scope = both;

alter system set db_recovery_file_dest='/u01/oradata/KMDB/fra' scope = both

*

ERROR at line 1:

ORA-02097: parameter cannot be modified because specified value is invalid

ORA-19802: cannot use DB_RECOVERY_FILE_DEST without DB_RECOVERY_FILE_DEST_SIZE

Cause:- 
This error occurs when we try to set DB_RECOVERY_FILE_DEST without setting the database recovery destination size parameter DB_RECOVERY_FILE_DEST_SIZE 

Solution:-
Set the database recovery destination size parameter DB_RECOVERY_FILE_DEST_SIZE 
SQL> alter system set db_recovery_file_dest_size=2g scope = both;

Case 3:- Database is open while enabling archivelog mode  

SQL> alter database archivelog; 

*
ERROR at line 1:

ORA-01126: database must be mounted in this instance and not open in any

instance

Cause:-

This error happens when you try to enable archivelog mode when the database is in open state 

Solution:- 

Shutdown the database and start the database in mount state. Then try to enable archivelog mode, it should work