Description of the diagram titled Rolling Forward and Rolling Back

The diagram shows a database requiring instance recovery. The database contains both committed and uncommitted transactions. The changes from the online redo log file are applied to the database. The online redo log file contains changes that are in the data file and changes that are not in the data file. It also contains both committed and uncommitted changes. This is called rolling forward. Uncommitted changes are then rolled back. The result is a recovered database that contains only committed transactions.