> It’s also not the case that heat is symmetric with size, in fact in an inverted index single entries can be very hot. I think you mixed two orthogonal topics

> It’s also not the case that heat is symmetric with size, in fact in an inverted index single entries can be very hot. I think you mixed two orthogonal topics: you first talked about frequent tokens, and now switched to hot keys(tokens which are frequently queried). As for frequent tokens, I think I well described algorithm, and it looks simple, and I don't see any issues there, if your metadata store (where you store info about shards and replicas) allows some kind of transactions (e.g. cocroachdb or similar). For hot keys/shards, as you pointed out, solution is to increase replication factor, but I think if shard is relatively small(10m IDs as in my example), adding another replica online is also fast, can be done in single transaction, and may not require all these movement you described.