Difference between revisions of "Flashback"

Latest revision as of 17:20, 6 January 2016

Enable Flashback while database is open (11g+)[edit]

SYS@EUDSTGP2> show parameter recover

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      /oracle/EUDSTGP2/fra
db_recovery_file_dest_size           big integer 4122M
db_unrecoverable_scn_tracking        boolean     TRUE
recovery_parallelism                 integer     0

SYS@EUDSTGP2> show parameter flash

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flash_cache_file                  string
db_flash_cache_size                  big integer 0
db_flashback_retention_target        integer     1440

SYS@EUDSTGP2> select flashback_on, status from v$database, v$instance;

FLASHBACK_ON       STATUS
------------------ ------------
NO                 OPEN

SYS@EUDSTGP2> alter database flashback on;

Database altered.

SYS@EUDSTGP2> select flashback_on, status from v$database, v$instance;

FLASHBACK_ON       STATUS
------------------ ------------
YES                OPEN

SYS@EUDSTGP2> 

Enable flashback[edit]

exec dbms_flashback.enable;

Disable flashback[edit]

exec dbms_flashback.disable;

Put a session back in time[edit]

Note: undo_management must be auto
Note: Take a look at undo_retention to get an idea of how far back you might be able to go.

exec dbms_flashback.enable_at_time(to_date('24-AUG-2012 12:00:00', 'DD-MON-YYYY HH24:MI:SS'));

Set the database recovery directory and size[edit]

alter system set db_recovery_file_dest='<path>' scope=both;
alter system set db_recovery_file_dest_size=<size> scope=both;

Use flashback to recover data deleted from a table[edit]

create table as_it_was_before
as select *
from ruined_table
as of timestamp to_timestamp ( '24-AUG-12 12:00:00', 'DD-MON-YY HH24:MI:SS' );

Enable flashback on Standby database[edit]

select flashback_on from v$database;
alter system set db_recovery_file_dest_size=50G scope=both;
alter system set db_recovery_file_dest=’/<directory>/’
shutdown immediate;
startup mount;
alter database flashback on;
show parameter db_flashback_retention_target;
alter system set db_flashback_retention_target=2880 scope=both;
alter database recover managed standby database cancel;

How far back can we flashback the database?[edit]

col oldest_flashback_scn for 99999999999999999
select	oldest_flashback_scn scn
,	to_char(oldest_flashback_time, 'DD-MON-YYYY HH24:MI:SS') oldest_time
from	v$flashback_database_log
/