Hi Michael,
There are actually two available methods. On the Database settings screen, you can select whether you want it to perform backups using mysqldump or by using pure PHP/WordPress database functions.
It backs up each database table to it's own file, so that a change to one table won't require the entire database to be committed again.
You can find these files in the wp-content/uploads/revisr-backups directory.
Hope that helps!