cassandra token range

Prior to Cassandra 1.2, every node was allocate to a particular token range.
Instead of a node being responsible for one large range of tokens, it is responsible for many smaller ranges.
In this way, one physical node is essentially hosting many smaller “virtual” nodes.
One of the new features slated for Cassandra 1.2’s release later this year is virtual nodes (vnodes.)
Vnodes:
- If you recall how token selection works currently, there’s one token per node, and a node owns exactly one contiguous range in the ring space.
Vnodes modify this paradigm from one token per node to many token per node.
Within a cluster these can be randomly selected and be non-contiguous, giving us many smaller ranges that belong to each node.

Advantages of virtual nodes

Tokens are automatically measured and allocate to every node.
when adding or removing nodes Re-balancing a cluster is automatically accomplished.
When a node merge the cluster, it assumes responsibility for an even portion of data from the other nodes in the cluster.
If a node fails, the load is develop evenly across other nodes in the cluster.
Number of vNodes can be set as node level.