How to Enable Oracle Database Flashback

Edited 3 weeks ago by ExtremeHow Editorial Team

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In this guide, we are going to explore how to enable Oracle Database Flashback. This is a powerful feature that allows database administrators and users to view the previous state of data or undo changes at the database level. It is a valuable tool for diagnosing and recovering from human errors, and it can save a lot of time and effort that would otherwise be spent on data recovery operations.

Understanding Oracle Flashback technology

Oracle Flashback Technology provides several features that allow you to view the previous state of your data or roll back your database to a previous point in time. This is particularly useful for recovering from accidental data changes or deletions, without performing a full database restore. Oracle Flashback Technology includes several features such as Flashback Query, Flashback Table, Flashback Drop, and Flashback Database, etc.

Pre-requisites to enable Flashback

Before you can enable Flashback features, you need to meet a few pre-requisites:

• You must have appropriate administrative privileges.
• Your database must be running in ARCHIVELOG mode, which means that archiving of the redo log is enabled.
• You need enough space in your Fast Recovery Area (FRA).

Steps to enable flashback in Oracle Database

Step 1: Check the ARCHIVELOG mode

Flashback Database relies on archived redo logs, so the database must be in ARCHIVELOG mode. To verify the ARCHIVELOG state, execute the following command as a user with SYSDBA privileges:

SQL> SELECT log_mode FROM v$database;

If the database is not in ARCHIVELOG mode, you must enable it. Follow these steps to enable ARCHIVELOG mode:

SHUTDOWN IMMEDIATE; 
STARTUP MOUNT; 
ALTER DATABASE ARCHIVELOG; 
ALTER DATABASE OPEN;

Step 2: Configure the Flash Recovery Area (FRA)

The next step is to configure the Fast Recovery Area (FRA), which Oracle uses to store flashback logs, archived redo logs, and other recovery-related files.

ALTER SYSTEM SET DB_RECOVERY_FILE_DEST = '/path/to/fra' SCOPE=BOTH; 
ALTER SYSTEM SET DB_RECOVERY_FILE_DEST_SIZE = 10G SCOPE=BOTH;

Replace '/path/to/fra' with the actual path you want to specify for the fast recovery area, and 10G with the actual size you want to allocate.

Step 3: Enable Flashback Database

Once you have configured your FRA, you can enable the Flashback Database feature. This is done when the database is in mount mode:

SHUTDOWN IMMEDIATE; 
STARTUP MOUNT; 
ALTER DATABASE FLASHBACK ON; 
ALTER DATABASE OPEN;

Once this is done, your database is now capable of moving the entire database back in time to a restore point or a specified timestamp using Flashback Database.

Step 4: Verify Flashback Settings

After enabling Flashback Database, it is good practice to verify that everything is set up correctly. To check this, use the following SQL query:

SQL> SELECT flashback_on FROM v$database;

The expected result is 'YES', which indicates that flashback is enabled. Additionally, verify your flash recovery area settings:

SQL> SHOW PARAMETER db_recovery_file_dest; 
SQL> SHOW PARAMETER db_recovery_file_dest_size;

These should reflect the settings you applied previously.

Step 5: Creating a restore point

You can optionally create restore points so that there are defined points to which Oracle Database can flashback. The restore point acts as a bookmark that you can use during a recovery operation:

SQL> CREATE RESTORE POINT before_major_update GUARANTEE FLASHBACK DATABASE;

With GUARANTEE FLASHBACK DATABASE, you ensure that enough flashback log data is retained to flashback to this restore point at any time.

Common Use-Cases for Flashback

There are several practical scenarios where flashback is particularly useful:

• Accidental data changes: If a DML operation such as DELETE, UPDATE or INSERT is executed incorrectly, a flashback query can be used to view the previous data. To quickly reverse the changes, a flashback table is beneficial.
• Logical corruption: Flashback Database can be used to move the entire database back in time to fix the error at the logical level without affecting the physical files.
• Testing and development: Developers often need to revert databases to a prior state during testing cycles; flashback features can make this process rapid and painless.

Limitations and considerations

Although Oracle Flashback technology is powerful, it still has its limitations and considerations:

• Flashback tasks require additional storage, so it is necessary to monitor the disk space usage of the fast recovery area.
• FlashBack Database does not protect against media failures; you still need a regular backup strategy.
• Not all data types and schema modifications are supported by the flashback operation. For example, some LOB data cannot be completely flashed back.
• Flashback retains its logs as long as possible, but they can be overwritten if space in the recovery area runs out.

Conclusion

Enabling and using Oracle Flashback Technology reduces downtime and recovery time in case of human errors, making it indispensable for database administrators. By following the steps outlined in this guide, you can confidently set up and manage Flashback in your Oracle environment.

Always remember to keep an eye on the size of your recovery area and manage retention to ensure smooth operation. When flashback is enabled, your database gains powerful capabilities in terms of data protection and recovery, but it should be implemented as one component of a multifaceted backup and recovery strategy.

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