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js 实现raft

2026-03-13 20:47:50JavaScript

Raft 算法简介

Raft 是一种分布式一致性算法，用于管理复制日志的一致性。它将一致性问题分解为领导选举、日志复制和安全性三个子问题，相比 Paxos 更易于理解和实现。

实现 Raft 核心模块

状态定义

js 实现raft

class RaftNode {
  constructor(id) {
    this.id = id;
    this.state = 'follower'; // follower/candidate/leader
    this.currentTerm = 0;
    this.votedFor = null;
    this.log = [];
    this.commitIndex = 0;
    this.lastApplied = 0;
    // 其他必要状态变量...
  }
}

选举超时处理

startElection() {
  this.state = 'candidate';
  this.currentTerm++;
  this.votedFor = this.id;

  const request = {
    term: this.currentTerm,
    candidateId: this.id,
    lastLogIndex: this.log.length - 1,
    lastLogTerm: this.log.length > 0 ? this.log[this.log.length-1].term : 0
  };

  // 向其他节点发送 RequestVote RPC
  this.peers.forEach(peer => {
    peer.requestVote(request, (response) => {
      if (response.term > this.currentTerm) {
        this.stepDown(response.term);
        return;
      }
      if (response.voteGranted) {
        this.votes++;
        if (this.votes > this.peers.length / 2) {
          this.becomeLeader();
        }
      }
    });
  });
}

日志复制

js 实现raft

appendEntries(entries) {
  if (this.state !== 'leader') return;

  const prevLogIndex = this.log.length - 1;
  const prevLogTerm = prevLogIndex >= 0 ? this.log[prevLogIndex].term : 0;

  const request = {
    term: this.currentTerm,
    leaderId: this.id,
    prevLogIndex,
    prevLogTerm,
    entries,
    leaderCommit: this.commitIndex
  };

  this.peers.forEach(peer => {
    peer.appendEntries(request, (response) => {
      if (response.success) {
        this.matchIndex[peer.id] = prevLogIndex + entries.length;
        this.nextIndex[peer.id] = this.matchIndex[peer.id] + 1;
        this.updateCommitIndex();
      } else {
        this.nextIndex[peer.id]--;
      }
    });
  });
}

关键注意事项

选举限制 只有包含最新日志的候选者才能赢得选举。检查候选者的日志是否至少与接收者的日志一样新：

function isLogUpToDate(candidateLastLogTerm, candidateLastLogIndex, 
                      currentLastLogTerm, currentLastLogIndex) {
  return candidateLastLogTerm > currentLastLogTerm ||
         (candidateLastLogTerm === currentLastLogTerm && 
          candidateLastLogIndex >= currentLastLogIndex);
}

安全性保证 领导者只能提交当前任期的日志条目，一旦该条目被存储在大多数服务器上，所有之前的条目都会被间接提交。