Virtual nodes in Cassandra 1.2

Cassandra 1.2 introduces virtual nodes (vnodes), a new feature that changes the token selection paradigm from one token or range per node to many per node, allowing for smaller and non-contiguous ranges. This results in faster rebuilding of nodes after failure and more efficient disk failure handling due to parallelized validation phases and incremental data transfer. Vnodes also simplify the use of heterogeneous machines in a cluster by enabling proportional allocation of vnodes based on machine capacity, maintaining balance during transitions from older to newer hardware.