Definition

Consistent hashing is a technique to distribute keys across nodes so that minimal keys need to be moved when nodes join/leave.

Core concept

Hash keys to a large ring; each node owns portions of the ring. When a node is added/removed, only its immediate neighbors’ keys are remapped.

Use cases

Caching (Memcached) and sharding schemes. Helps rebalance gracefully.

Trade-offs

Key ownership changes on membership change; may need virtual nodes to balance load.

References

Web caching design.