算法学习之：Raft-分布式一致性/共识算法

基础介绍

Raft是什么？

Raft is a consensus algorithm that is designed to be easy to understand. It's equivalent to Paxos in fault-tolerance and performance. The difference is that it's decomposed into relatively independent subproblems, and it cleanly addresses all major pieces needed for practical systems. We hope Raft will make consensus available to a wider audience, and that this wider audience will be able to develop a variety of higher quality consensus-based systems than are available today.

 Raft 是一种易于理解的共识算法(Consensus Algorithm)。它在容错性和性能方面与 Paxos 相当。所不同的是，它被分解成了相对独立的子问题，并简洁地解决了实际系统所需的所有主要问题。我们希望 Raft 能让更多人了解共识（Consensus），也希望更多的人能够开发出比现在更高质量的基于共识的系统。

Consensus又是什么？

Consensus is a fundamental problem in fault-tolerant distributed systems. Consensus involves multiple servers agreeing on values. Once they reach a decision on a value, that decision is final. Typical consensus algorithms make progress when any majority of their servers is available; for example, a cluster of 5 servers can continue to operate even if 2 servers fail. If more servers fail, they stop making progress (but will never return an incorrect result).

Consensus typically arises in the context of replicated state machines, a general approach to building fault-tolerant systems. Each server has a state machine and a log. The state machine is the component that we want to make fault-tolerant, such as a hash table. It will appear to clients that they are interacting with a si