I have a database that process a lot of transaction late at night. It is set to full recovery mode. Every night I do a full backup of the database, but the log file does not empty out. It just continues to grow and never seems to release old transactions after a backup. As a quick fix, which i don't like, I will temporarily switch recovery mode to simple->truncate log file->set recovery mode to full->then full backup of database. Any ideas why the transaction log does not empty out after a full backup and continues to grow?