IIRC this is the kind of problem that CockroachDB seems to solve well, given their implementation of range partitioning with automatic rebalancing. This ensures

IIRC this is the kind of problem that CockroachDB seems to solve well, given their implementation of range partitioning with automatic rebalancing. This ensures the partitions are evenly distributed even with an uneven customer distribuiton. I have no affiliation with the product, but I have been comparing alternatives and it seems like that's where it shines.