Oracle’s Flashback technologies provide powerful tools for data recovery in advanced scenarios, allowing you to recover lost data even after it has been deleted or modified. In this answer, I’ll describe the three main Flashback technologies – Flashback Query, Flashback Table, and Flashback Database – and explain how they can be used to recover data.
Flashback Query: Flashback Query allows you to view data as it existed at an earlier point in time, using the AS OF TIMESTAMP or AS OF SCN clause in a SQL query. This can be useful for recovering data that has been accidentally deleted or modified, as it allows you to see the values of data at the specific point in time before it was lost. For example, let’s say that an employee table is accidentally modified at 2:00pm, and you want to recover the data as it existed at 1:00pm. Using Flashback Query, you can run the following SQL query:
SELECT *
FROM employees
AS OF TIMESTAMP TO_TIMESTAMP('2021-11-01 13:00:00', 'YYYY-MM-DD HH24:MI:SS');This will show you the values of the employee table as they existed at 1:00pm, allowing you to recover the lost data.
Flashback Table: Flashback Table allows you to revert a table to a previous state, using the FLASHBACK TABLE or the DBMS_FLASHBACK package. This can be useful if you want to recover data from a specific point in time, or if you want to undo a mass update or delete operation. For example, let’s say that a mass delete operation was run on the employee table, and you want to recover the deleted data. Using Flashback Table, you can run the following SQL command:
FLASHBACK TABLE employees TO BEFORE DROP;This will revert the employee table to its state prior to the drop operation, allowing you to recover the deleted data.
Flashback Database: Flashback Database allows you to recover an entire database to a previous point in time, using the RMAN utility. This can be useful if there has been a catastrophic failure of your database, or if you want to recover from a point in time that is not covered by your regular backup strategy. For example, let’s say that there is a major issue with your database at 2:00pm, and you want to recover the database to its state at 1:00pm. Using Flashback Database, you can run the following RMAN command:
FLASHBACK DATABASE TO TIMESTAMP TO_TIMESTAMP('2021-11-01 13:00:00', 'YYYY-MM-DD HH24:MI:SS');This will recover the entire database to its state as it existed at 1:00pm, allowing you to recover any data that was lost due to the issue at 2:00pm.
Overall, Oracle’s Flashback technologies provide powerful tools for data recovery in advanced scenarios, allowing you to recover data at the level of a single SQL query or an entire database. By understanding the capabilities of these technologies, you can ensure that your data is protected against accidental or malicious data loss.