Well, actually the server doesn't know the ordering and how pieces of B-Tree refer to each other, it doesn't even know which data form the index and which are t

Well, actually the server doesn't know the ordering and how pieces of B-Tree refer to each other, it doesn't even know which data form the index and which are the actual data. Though, observing access patterns, it could probably deduce which data belong to the tree and some info about ordering (which will hold true until we re-balance the tree, which happens on inserts). I think, if we change objects each time we do queries, we can prevent this data leak.