Difference Between Redo and Undo in Oracle Database

Redo refers to a set of logs that record all changes made to the database, including inserts, updates, and deletes. These changes are written to the redo log buffer and then to the redo log files, ensuring that Oracle can recover committed transactions in the event of a system failure.

Undo

On the other hand, undo is used to reverse the effects of uncommitted transactions. When a transaction is rolled back, the undo data allows Oracle to restore the original data values. Undo is also essential for providing consistent reads to other users by preserving a snapshot of the data before changes were made.

In summary, redo helps in reapplying committed changes after a crash, while undo helps in rolling back uncommitted changes and supporting read consistency.

 

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