If additional checkpoint dump files are needed in the online mode, reserved file groups are automatically opened and placed on overwritable status. This is implemented by specifying jnl_reserved_file_auto_open=Y in the checkpoint dump service definition.

The automatic opening function is executed when the number of remaining checkpoint dump files in use decreases to the guaranteed number of generations. A file once opened (including those which could not be successfully opened) can no longer be opened automatically.