def raise_on_session_data_overflow!
      return false unless loaded?
      limit = self.class.data_column_size_limit
      if limit and read_attribute('data').size > limit
        raise ActionController::SessionOverflowError
      end
    end
def raise_on_session_data_overflow!
      return false unless loaded?
      limit = self.class.data_column_size_limit
      if limit and read_attribute('data').size > limit
        raise ActionController::SessionOverflowError
      end
    end
Ensures that the data about to be stored in the database is not
 larger than the data storage column. Raises
 ActionController::SessionOverflowError.