Data partitioning

Splitting rows across machines. The shard key decides everything: even spread, hot shards, and which queries touch every shard.

A key's hash picks its node. Even, but with plain mod N adding one node moves most keys; fixed slots fix that.

Each node owns a contiguous range of keys. Range queries touch few nodes; rising keys pile onto the last range.

A lookup table says which shard holds each key. Any placement you like, at the cost of one more lookup.

Nodes and keys sit on a ring, so adding or removing a node moves only a small share of the keys.

Every node scores each key and the highest score wins. The same small movement as a ring, with no ring to keep.