When a node fails or is removed, what happens to the keys it was responsible for?

When a node fails or is removed, what happens to the keys it was responsible for?

• A. The displaced keys are reassigned to the next node clockwise.
• B. All keys are redistributed evenly across all remaining nodes.
• C. No keys move after removal.
• D. The keys migrate to the previous node on the ring.

Answer: (A)

This question tests how consistent hashing handles node churn. In a consistent-hash ring, each key is assigned to the first node clockwise from its hash value. When a node fails, only the keys that hashed to that node need new homes, and they are moved to that node’s successor—the next node clockwise on the ring. This keeps the mapping stable for the rest of the keys and minimizes movement. So the displaced keys are reassigned to the next node clockwise. Moving all keys, leaving them unmoved, or sending them to the previous node would break the ring’s ownership rule and disrupt the efficient redistribution that consistent hashing provides.

This question tests how consistent hashing handles node churn. In a consistent-hash ring, each key is assigned to the first node clockwise from its hash value. When a node fails, only the keys that hashed to that node need new homes, and they are moved to that node’s successor—the next node clockwise on the ring. This keeps the mapping stable for the rest of the keys and minimizes movement. So the displaced keys are reassigned to the next node clockwise. Moving all keys, leaving them unmoved, or sending them to the previous node would break the ring’s ownership rule and disrupt the efficient redistribution that consistent hashing provides.