Why it matters

Bad partitioning causes hot nodes and uneven cluster load. Understanding it prevents this and lets you reason about capacity.

Advertisement

The architecture

Murmur3Partitioner: default partitioner. Hashes partition keys to a 64-bit token space.

Token ring: 64-bit hash range viewed as a circle. Nodes own ranges of tokens; keys hashed into their range are stored on that node.

Cassandra partitioningPartition keyhashed via Murmur3Token ringhash spaceNode owns rangevnodes for smoothing256 vnodes per physical node typical; enables smooth rebalancing when nodes added
Distribution mechanism.
Advertisement

How it works end to end

Virtual nodes: each physical node owns many (256 default) hash ranges. Adding a node redistributes ranges evenly. Smoother than manual token assignment.

Replication factor: rows replicated to N nodes on the ring after the primary. Ensures durability across node failures.

Rack-aware placement: replicas placed on different racks (physical availability domains) for fault tolerance.