When a new node is added, which keys move?

When a new node is added, which keys move?

• A. Only keys in the arc between the new node and its counter-clockwise neighbor move to the new node.
• B. All keys migrate to the new node.
• C. No keys move at all.
• D. Only keys on the next clockwise node move.

Answer: (A)

In consistent hashing, every key is stored on the first node encountered when moving clockwise around the hash ring from the key’s hash. When a new node is added, only the keys whose hashes lie in the interval between the new node and its predecessor (the counter-clockwise neighbor) are reassigned to the new node. All other keys remain on their existing nodes. So the keys that move are precisely those in the arc between the new node and its counter-clockwise neighbor. This is why the correct option points to that specific arc. The other options would imply moving all keys, none, or only keys from the next clockwise node, which isn’t how consistent hashing reallocates data.

In consistent hashing, every key is stored on the first node encountered when moving clockwise around the hash ring from the key’s hash. When a new node is added, only the keys whose hashes lie in the interval between the new node and its predecessor (the counter-clockwise neighbor) are reassigned to the new node. All other keys remain on their existing nodes. So the keys that move are precisely those in the arc between the new node and its counter-clockwise neighbor. This is why the correct option points to that specific arc. The other options would imply moving all keys, none, or only keys from the next clockwise node, which isn’t how consistent hashing reallocates data.