private int compare(Revision a, Revision b) {
if (Arrays.equals(a._id, b._id)) return 0;
Version va = getVersion(a);
Version vb = getVersion(b);
int n = va.compareTo(vb);
if (n != 0) return n;
if (a.created != b.created) return a.created > b.created ? 1 : -1;
for (int i = 0; i < a._id.length; i++)
if (a._id[i] != b._id[i]) return a._id[i] > b._id[i] ? 1 : -1;
return 0;
}
