Without a materialized view log, Oracle Database must reexecute the materialized view query to refresh the materialized view. This process is called a complete refresh. Usually, a complete refresh takes more time to complete than a fast refresh or a synchronous refresh.
A materialized view log is located in the master database in the same schema as the master table. A master table can have only one materialized view log defined on it.
Commit SCN-based materialized view logs use commit SCN data rather than timestamps, which removes the need for the setup operations and thus can improve the speed of the materialized view refresh.
If you specify the COMMIT SCN clause, then a commit SCN-based materialized view log is created.