Lightweight transactions in Cassandra 2.0

The text discusses the concept of linearizable consistency in distributed systems and how it can be achieved using the Paxos consensus protocol. Linearizability ensures that operations appear to occur atomically, one at a time, even if they are executed concurrently. This is crucial for applications like user registration where ensuring uniqueness is important. The Paxos protocol allows a distributed system to agree on proposals with a quorum-based algorithm, without the need for a master node or two-phase commit problems. It consists of three phases: prepare/promise, propose/accept, and commit/acknowledge. Cassandra uses this protocol to provide linearizability in its lightweight transactions feature, which can be used for both INSERT and UPDATE statements with the new IF clause.