Oracle Flashback Technology provides a way to revert database entries to a previous state without performing a traditional recovery from backup.
According to Oracle, Flashback Technology has the following capabilities:
- Performs queries that return past data.
- Performs queries that return metadata that displays a detailed history of changes to the database contents.
- Rolls back tables and rows to a previous point in time.
- Automatically tracks and archives transactional data changes.
- Rolls back a transaction, plus its dependent transactions, while the database remains online.
Oracle Flashback is not a backup, nor is it designed to be a backup replacement. All the capabilities listed above can be realized without creating a traditional backup or performing a restoration. At the same time, Flashback does nothing to protect the database against storage failure, corruption or other forms of data loss.
Given Oracle Flashback's name and capabilities, it is easy to assume that flashback technology is based on the use of snapshots. However, the technology does not use snapshots.
Oracle Flashback Technology is based around a database feature called Automatic Undo Management. You are probably familiar with the undo feature found in applications such as Microsoft Office. Office and similar applications keep track of user actions so those actions can be undone if necessary. Oracle does something very similar. When a user executes an update statement within an Oracle database, any values that are about to be overwritten are copied to the database's undo data. The undo data is a persistent part of the database and can be used to roll back transactions or perform any of the listed functions.
Oracle Flashback Transaction Query tool can repair database changes
Oracle Data Recovery Advisory tips for data recovery failures
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