Right. This spanner thing is new to me, but looking at it, I don't see why spanner doesn't/couldn't shard by modulo / checksum to reduce this risk. And I think other systems do
Good point. I guess it would be cool if you could choose the sharding method per-table. I haven't put too much thought into this, but off the top of my head I can imagine a number of different methods suitable for different situations.
