Page History

...

• For databases which are operating in the full or bulk logged recovery model, the log file will grow indefinitely until a backup is taken. In this case, you need to back up your log file and either schedule regular backups to continue, or consider changing the

  Newtablink
  alias recovery model url http://msdn.microsoft.com/en-us/library/ms189275.aspx

   of log truncation of your database to better fit your needs.
• For databases of any recovery model, a long running transaction will prevent the log from being truncated. You may need to identify and either commit or kill the offending transaction, or in the case of an important business transaction, you may need to grow the log file to allow it to finish.

...