$self->{dbh}->sqlite_backup_to_file($fn);
$tmp = ref($self)->new_file($fn, 2);
$tmp->{dbh}->do('PRAGMA journal_mode = MEMORY');
$self->{dbh}->sqlite_backup_to_file($fn);
$tmp = ref($self)->new_file($fn, 2);
$tmp->{dbh}->do('PRAGMA journal_mode = MEMORY');