sub _mk_db_closure {
	my ($class, $dsn, $user, $pass, $attr) = @_;
	$attr ||= {};

	my $dbh;
	my $process_id = $$;
	return sub {
		# set the PID in a private cache key to prevent us
		# from sharing one with the parent after fork. This
		# is better than disconnecting the existing $dbh since
		# the parent may still need the connection open. Note
		# that forking code also needs to set InactiveDestroy
		# on all open handles in the child or the connection
		# will be broken during DESTROY.
		$attr->{private_cache_key_pid} = $$;

		# reopen if this is a new process or if the connection
		# is bad
		if ($process_id != $$ or not ($dbh && $dbh->FETCH('Active') && $dbh->ping)) {
			$dbh = DBI->connect_cached($dsn, $user, $pass, $attr);
			$process_id = $$;
		}
		return $dbh;
	};
}