The undo log entries for transactions are written and managed in undo log management. The database system uses the undo log entries to reinstate a database with a consistent transaction status that corresponds to the status that existed at the time of the most recent savepoint.
A user task always writes undo log entries when it carries out modifying SQL statements. It stores the undo log entries in its undo log file.
See also:
Using Log Entries at Restart or Recovery