Oracle Internal Arch. (contd.)
- store ‘before image’ of the data modified by the transactions for restoring the data in case of transaction failure or rollback. This information is not required after a transaction commits & hence that portion of segment can be reused for another transaction.
- also used for providing ‘read consistency’ across multiple transactions so that they can get original data and not the dirty / uncommitted data. Oracle transactions do not require to give ‘repeatable read’ isolation level; it is always provided.