http://oracle-db-admin.blogspot.in/2009/09/what-is-checkpoint.html

Checkpoint automatically occurs at:1.Checkpoint automatically occurs at a log switch.2.When we will specify the parameter fast_start_mttr_target=.3.When Normally forced by the Database Administrator.4.If the datafile is offline checkpoint will occur.http://oracle-db-admin.blogspot.in/2009/09/what-is-checkpoint.html