Postgres at least will store rows roughly in insert order. So whether you're using integers or UUIDs for primary keys won't affect on-disk layout. When scannin

Postgres at least will store rows roughly in insert order. So whether you're using integers or UUIDs for primary keys won't affect on-disk layout. When scanning the index, the database will be traversing it in btree order, anyway, so as long as the values are comparable, ints or UUIDs shouldn't matter much.