For DB Observer 3 types of operations are allowed: last-n: Keep track of the last transactions going to the database. Unlike journal, this just keeps a finite, well-known number of transactions. count: Make a count of the number of operations going to the database. * journal: Register all the operations going to the database in a buffer. The content can be dumped in a file later. This column value can be empty. If this column is left empty, the rule will not be activated and an error will be shown under status['error'].