Paxos Made Simple
📜 Abstract
The Paxos algorithm, when presented in plain English, is very simple. The architecture divides nodes into three roles: client, acceptor, and proposer. Consensus is reached in two phases: prepare; accept. Prepare phase: a proposer selects a proposal identifier and sends a prepare request to a quorum of acceptors. If acceptor has not responded to any other prepare requests with a higher identifier, it responds with a promise and the highest-numbered proposal it has accepted (if any). Otherwise, it ignores the request. In accept phase, proposer sends accept requests for a specific proposal number. If an acceptor receives an accept request for a proposal number that matches the one in the promise, it accepts the proposal. Otherwise, it rejects the request. Once a proposal has been accepted by a quorum of acceptors, the decision is reached. This protocol is fault-tolerant and can achieve consensus even if some nodes are unresponsive.
✨ Summary
The paper “Paxos Made Simple” by Leslie Lamport, published in December 2001, presents a simplified explanation of the Paxos consensus algorithm. Paxos is crucial in distributed systems for achieving consensus despite failures. The algorithm outlines roles for nodes and describes a two-phase process using phases ‘prepare’ and ‘accept’.
Paxos is influential in the design and implementation of distributed computing and fault-tolerant systems. It has impacted numerous systems and protocols including Google’s Chubby lock service (Burrows, 2006), Amazon’s Dynamo (DeCandia et al., 2007), and the Raft consensus algorithm (Ongaro and Ousterhout, 2014), which was developed as a more understandable alternative. These systems utilize the principles of Paxos to ensure reliability and availability across distributed nodes. Overall, Paxos remains a foundational element in the field of distributed computing, continuously being referenced and adapted for new technologies and research in resilient consensus mechanisms.