Understanding the Hash Ring in Consistent Hashing
If you’ve ever looked into distributed systems or scalable caching, you’ve probably heard the term hash ring . It’s at the heart of consistent hashing — the algorithm that powers systems like DynamoDB, Cassandra, Riak, and distributed caches such as Memcached and Redis Cluster. In this post, we’ll break down what a hash ring is, how it works, and why it matters. What Is a Hash Ring? A hash ring is a conceptual circle that represents the entire range of hash values. Imagine the numbers from 0 to 2³² − 1 arranged in a circle. Nodes (servers) : Each server in your cluster is hashed to a point on the ring based on its identifier (e.g., IP address). Keys (data items) : Each key you want to store (e.g., cache key, user ID) is also hashed to a point on the ring. Assignment rule : A key is assigned to the first server found clockwise from its hash position. https://ably.com/blog/implementing-efficient-consistent-hashing Adding a Node When you add a new node: Hash the node’...