Consistent Hashing in 1 diagram and 198 words
Explained as simply as possible… but not simpler.
A hashing technique that distributes data across nodes in a way that minimizes reassignments when nodes are added or removed.
In distributed systems (like caches, databases, or object stores), data must be spread across many nodes. When scaling up or down, we want to avoid reassigning all data. Consistent hashing helps by minimizing the impact of these changes.
Use consistent hashing when building scalable systems where nodes can dynamically be added or removed (e.g., distributed caches, sharded databases).
You need to know
Hash Ring Structure: Hash both data and servers into a circular space (0 to 2ⁿ-1). This is called the hash ring.
Data Mapping Rule: A data item is stored on the first server found clockwise from its hash position on the ring.
Virtual Nodes: Each server is mapped to multiple points (virtual nodes) on the ring to avoid uneven distribution (hotspots).
Popular technologies
Amazon DynamoDB – Distributed NoSQL database using consistent hashing for partitioning and fault tolerance.
Apache Cassandra – Peer-to-peer database that uses consistent hashing for data placement and replication.
Redis Cluster – Uses a form of consistent hashing to split keyspace and balance load across Redis nodes.
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