Google Drive: A Beginner's Guide to Paxos
The core ideas of Paxos protocol: 1) Optimistic concurrency control (variant 2). Hold a "preemptible lock" first, try updating, restart on denial; 2) Quorum as a logical unit of acceptor for choose operation. A value is chosen iff it's accepted by a quorum, which implies from the proposer's perspective the choose operation is atomic, it's all or nothing, it's either accepted by a quorum or it isn't.