Our Cassandra schema is using int data type for the tile indexes. The 31bit (+signed) int limits us to zoom15 (4^15 is a 30bit value)
We could either store all indexes as 64bit ints, or we could have two tables - 32bit for zoom<=15, and 64bit for >15.
Do we want to save one more byte here and go with two tables? Guestimating about 70m tiles, so 70MB more of pure data, plus whatever's extra?