Transaction logs contain the record of Microsoft SQL Server database activity . Transaction log backup is a backup for log files of a database . Backing up the transaction log periodically to create a sequence of transaction log backups offers users the most flexibility in restoring databases. By creating transaction log backups, a database can be restored to any point in time contained within the sequence of transaction logs, right up to the point of failure , because it is possible to back up the currently active transaction log even if the database is inaccessible.

Note : After you have modified the structure or configuration of the database (for example, by adding more data or log files, or changing the recovery model), you must perform a full database backup before performing a differential or Transaction log backup.

A full database backup is required before you perform transaction log backup . Every time you back up transaction log , program always backs up the new added items in log files . You have three options when you backup a transaction log :

• Remove inactive entries from transaction log -- Truncates the inactive portion of the the log files .SQL Server then reuses this truncated, unused space in the transaction log rather than the transaction log continuing to grow and use more space
• Do not remove inactive entries from transaction log -- Retains inactive log entries after backup .
• Back up the tails of the log , and leave the database in the restoring state -- This option is available for SQL Server 2000 or later , If you want your database is restored to the newest state or point of failure , please select this option to do a transaction log backup , and then use this new log backup to restore database.

Note : If the databases' recovery modal is "Simple" , you cannot do transaction log backup.