What is the gossip protocol in Cassandra?

Gossip is the peer-to-peer protocol Cassandra uses to let nodes discover and track the state of every other node without any central coordinator.

1. Every second, each node picks one to three other nodes at random and exchanges state information with them.
2. The state includes things like heartbeat version, node status (up/down/joining/leaving), load, and schema version.
3. Because the exchange is random and repeated constantly, information propagates through the whole cluster exponentially fast, even in clusters with hundreds of nodes.
4. Seed nodes are just a bootstrap list new nodes contact first to join the gossip network; they hold no special ongoing authority afterward.

Gossip is also the transport for cluster membership and failure detection: version numbers let a node tell whether the information it just received is newer than what it already knows, so stale rumors don't overwrite fresh state.

This decentralized design is a core reason Cassandra has no single point of failure at the cluster-management layer — there is no master to elect or lose.