Is The Transaction Log Truncated When Doing a Backup In Full Recovery Mode?

Question

Is the database transaction log automatically truncated after we create a backup and the DB is in full recovery mode? Or do we need to make 2 different backups, let's say 1 in full recovery mode and a different one for the log file.

Answer 1

The T-Log will only have portions of it marked inactive, when the database has a transaction log backup on it performed - a portion (vlf) is only marked inactive if there are no outstanding transactions within the VLF. A full backup, whether in fully logged mode or bulk logged mode will not mark any portions of the t-log inactive.

Paul Randal devoted an entire post to this question before : http://www.sqlskills.com/BLOGS/PAUL/post/Misconceptions-around-the-log-and-log-backups-how-to-convince-yourself.aspx