When you redo a transaction, the changes made by a successful transaction are repeated. The database is switched to the consistent state it had at the end of the transaction.
The information required to redo the transaction is stored by the database system in the redo log entries (also known as “after-image entries”). The redo log entries are first stored permanently in the log area by the COMMIT of the transaction.
See also:
Concepts of the Database System
· Using Log Entries for a Restart or Recovery