# Throw away all keys in old hash that are in new, update keys that changed or are new
foreach $key (keys %$new) {
    if (exists($old->{$key}) {
	if ($old->{$key} ne $new->{$key}) {
	    updateindatabase($key,$new->{$key});
	}
	delete $old->{$key};
    }
    else {
	updateindatabase($key,$new->{$key});
    }

# remove keys that are only in old
foreach  $key (keys %$old) {
    deleteindatabase($key);
}