> What parent mean is that there may be holes in the sequence of primary keys. Are you sure that's what they mean? It's not what they said. "Monotonic" means "

> What parent mean is that there may be holes in the sequence of primary keys. Are you sure that's what they mean? It's not what they said. "Monotonic" means "strictly increasing" (or decreasing) e.g. 1, 2, 5, 7 is monotonic even though it has gaps. "Contiguous" means "without gaps".