Oracle 19c Flashback Database Guide
Introduction to Oracle 19c Flashback Database
This guide provides step-by-step instructions for setting up and using the Oracle 19c Database Flashback feature to recover data or the entire database to a specific point in time or SCN.
Note: Before performing any of the following actions, always make sure to take a backup of your database to avoid data loss.
Prerequisites for Enabling Flashback Database
- ARCHIVELOG Mode: The database must operate in
ARCHIVELOG mode to support flashback operations.
- Database in MOUNT State: Place the database in the
MOUNT state before enabling Flashback.
- Flash Recovery Area (FRA): Set up a Flash Recovery Area with sufficient space to store flashback logs.
- Ample Disk Space: Ensure adequate storage is available in the FRA to meet your retention requirements.
Enable Database Flashback
Check Recovery Area for Flashback Log
$ sqlplus / as sysdba
SQL> SHOW RECYCLEBIN;
SQL> show parameter db_recovery_file_dest;
Create a Destination for Recovery Area & Configure Recovery File Destination and Size
$ mkdir /db_backup/db_recovery_file_dest
SQL> alter system set db_recovery_file_dest='/db_backup/db_recovery_file_dest' SCOPE=spfile;
SQL> alter system set db_recovery_file_dest_size=25G SCOPE=spfile;
Set Undo Retention
-- Check undo retention (in seconds)
SQL> SELECT TO_NUMBER(VALUE) / 60 AS "Undo Retention (minutes)"
FROM V$PARAMETER
WHERE NAME = 'undo_retention';
-- Set undo retention (e.g., 3600 seconds for 1 hour)
SQL> ALTER SYSTEM SET undo_retention = 3600 SCOPE=BOTH;
Set Flashback Retention Target & Enable Flashback
-- Set flashback retention in minutes (e.g., 4,320 for 3 days)
SQL> alter system set db_flashback_retention_target=4320;
-- Check flashback status
SQL> select flashback_on from v$database;
-- Enable flashback
SQL> shutdown immediate;
SQL> startup mount;
SQL> alter database flashback on;
SQL> alter database open;
Obtain Current SCN and Timestamp for Test
SQL> SELECT current_scn, SYSTIMESTAMP FROM v$database;
Insert Test Data (for demonstration)
SQL> create user flash_user identified by flash_user;
SQL> grant connect, resource to flash_user;
SQL> GRANT UNLIMITED TABLESPACE TO flash_user;
SQL> ALTER USER flash_user QUOTA UNLIMITED ON users;
SQL> conn flash_user/flash_user;
SQL> create table test_ahosan (
id number(10) Primary key
);
SQL> insert into test_ahosan (id) values (1);
SQL> select * from test_ahosan;
Perform Database Flashback (to SCN or Timestamp)
Flashback to SCN (before user creation)
SQL> SELECT oldest_FLASHBACK_scn, oldest_FLASHBACK_time from v$flashback_database_log;
SQL> shutdown immediate;
SQL> startup mount;
SQL> Flashback database to scn 309817939;
SQL> Alter database open read only;
Flashback to Timestamp (before user creation)
SQL> shutdown immediate;
SQL> startup mount;
SQL> FLASHBACK DATABASE TO TIMESTAMP
TO_TIMESTAMP('2024-11-06 04:15:40', 'YYYY-MM-DD HH:MI:SS');
SQL> Alter database open read only;
Finalize Database State (Resetlogs)
SQL> shutdown immediate;
SQL> startup mount;
SQL> Alter database open resetlogs;
SQL> conn flash_user/flash_user;
SQL> select * from test_ahosan;
Best Practices for Flashback Database
- Set
DB_FLASHBACK_RETENTION_TARGET based on your recovery requirements.
- Monitor and maintain sufficient space in the Flash Recovery Area for your flashback logs.
- Perform flashback operations during low traffic periods to minimize system impact.
Conclusion
Oracle 19c Flashback Database offers a robust way to recover from data loss with minimal downtime. With proper configuration and maintenance, DBAs can use this feature to quickly address logical errors, boosting overall data management efficiency and resilience.