A file created to permit database recovery (or file recovery). The log contains information about all changes made to a database or file since it was last established as being correct and a backup copy was last taken. The form in which changes may be recorded in a recovery log may vary considerably, depending on the recovery algorithms to be used. In general, a recovery log may be used in one of two ways:

1. (a) to redo all changes since the last backup (if the database or file has been corrupted);

2. (b) to undo all incorrect changes (if the source of error is in the changes).