In addition to one or more data files, every database in a SQL Server instance has one or more log files that keep track of changes to that database. (In SQL Server 2005, database snapshots do not have log files because no changes are ever made directly to a snapshot.) SQL Server uses the transaction log to guarantee consistency of your data, at both a logical and a physical level. In addition, an administrator can make backups of the transaction log to make restoring a database more efficient. An administrator or database owner can also set a database’s recovery mode to determine the level of detail stored in the transaction log.