6.824（6.5840) 6.5840 Lab 3: Raft
本帖最后由 红月亮 于 2024-8-5 13:31 编辑6.5840 https://pdos.csail.mit.edu/6.824/labs/lab-raft.html
partB的日志复制无法通过测试，代码有什么可以改进的地方？
github地址:https://github.com/2451965602/6.5840
package raft
//
// this is an outline of the API that raft must expose to
// the service (or tester). see comments below for
// each of these functions for more details.
//
// rf = Make(...)
// create a new Raft server.
// rf.Start(command interface{}) (index, term, isleader)
// start agreement on a new log entry
// rf.GetState() (term, isLeader)
// ask a Raft for its current term, and whether it thinks it is leader
// ApplyMsg
// each time a new entry is committed to the log, each Raft peer
// should send an ApplyMsg to the service (or tester)
// in the same server.
//
import (
"github.com/sasha-s/go-deadlock"
// "bytes"
"math/rand"
"sync"
"sync/atomic"
"time"
// "6.5840/labgob"
"6.5840/labrpc"
)
// as each Raft peer becomes aware that successive log entries are
// committed, the peer should send an ApplyMsg to the service (or
// tester) on the same server, via the applyCh passed to Make(). set
// CommandValid to true to indicate that the ApplyMsg contains a newly
// committed log entry.
//
// in part 3D you'll want to send other kinds of messages (e.g.,
// snapshots) on the applyCh, but set CommandValid to false for these
// other uses.
type ApplyMsg struct {
CommandValid bool
Command interface{}
CommandIndex int
// For 3D:
SnapshotValid bool
Snapshot []byte
SnapshotTermint
SnapshotIndex int
}
type Entry struct {
Term int
Command interface{}
Index int
}
// A Go object implementing a single Raft peer.
type Raft struct {
mu deadlock.Mutex // Lock to protect shared access to this peer's state
peers []*labrpc.ClientEnd // RPC end points of all peers
persister *Persister // Object to hold this peer's persisted state
me int // this peer's index into peers[]
dead int32 // set by Kill()
// Your data here (3A, 3B, 3C).
state string
applyCh chan ApplyMsg
lastLeaderCheck time.Time
currentTerm int
votedFor int
logs []Entry
commitIndex int
lastApplied int
nextIndex []int
matchIndex[]int
voteCount int
// Look at the paper's Figure 2 for a description of what
// state a Raft server must maintain.
}
// return currentTerm and whether this server
// believes it is the leader.
func (rf *Raft) GetState() (int, bool) {
var term int
var isleader bool
// Your code here (3A).
term = rf.currentTerm
isleader = rf.state == "Leader"
//DPrintf("GetState: term=%d,me=%d,isleader=%v,state:%v", term, rf.me, isleader, rf.state)
return term, isleader
}
// save Raft's persistent state to stable storage,
// where it can later be retrieved after a crash and restart.
// see paper's Figure 2 for a description of what should be persistent.
// before you've implemented snapshots, you should pass nil as the
// second argument to persister.Save().
// after you've implemented snapshots, pass the current snapshot
// (or nil if there's not yet a snapshot).
func (rf *Raft) persist() {
// Your code here (3C).
// Example:
// w := new(bytes.Buffer)
// e := labgob.NewEncoder(w)
// e.Encode(rf.xxx)
// e.Encode(rf.yyy)
// raftstate := w.Bytes()
// rf.persister.Save(raftstate, nil)
}
// restore previously persisted state.
func (rf *Raft) readPersist(data []byte) {
if data == nil || len(data) < 1 { // bootstrap without any state?
return
}
// Your code here (3C).
// Example:
// r := bytes.NewBuffer(data)
// d := labgob.NewDecoder(r)
// var xxx
// var yyy
// if d.Decode(&xxx) != nil ||
// d.Decode(&yyy) != nil {
// error...
// } else {
// rf.xxx = xxx
// rf.yyy = yyy
// }
}
// the service says it has created a snapshot that has
// all info up to and including index. this means the
// service no longer needs the log through (and including)
// that index. Raft should now trim its log as much as possible.
func (rf *Raft) Snapshot(index int, snapshot []byte) {
// Your code here (3D).
}
// example RequestVote RPC arguments structure.
// field names must start with capital letters!
type RequestVoteArgs struct {
// Your data here (3A, 3B).
Term int
CandidateIdint
LastLogIndex int
LastLogTermint
}
// example RequestVote RPC reply structure.
// field names must start with capital letters!
type RequestVoteReply struct {
// Your data here (3A).
VoteGranted bool
Term int
}
type AppendEntriesArgs struct {
NewCommand bool
Term int
LeaderId int
PrevLogIndex int
PrevLogTermint
Logs []Entry
LeaderCommit int
}
type AppendEntriesReply struct {
Term int
Success bool
}
// example RequestVote RPC handler.
func (rf *Raft) RequestVote(args *RequestVoteArgs, reply *RequestVoteReply) {
// Your code here (3A, 3B).
rf.mu.Lock()
defer rf.mu.Unlock()
if rf.killed() {
reply.Term = -1
reply.VoteGranted = false
return
}
if args.Term < rf.currentTerm {
reply.Term = rf.currentTerm
reply.VoteGranted = false
return
}
if args.Term > rf.currentTerm {
rf.currentTerm = args.Term
rf.state = "Follower"
rf.votedFor = -1
}
lastLogIndex := len(rf.logs) - 1
lastLogTerm := 0
if lastLogIndex >= 0 {
lastLogTerm = rf.logs.Term
}
if (rf.votedFor == -1 || rf.votedFor == args.CandidateId) && (args.LastLogTerm > lastLogTerm || (args.LastLogTerm == lastLogTerm && args.LastLogIndex >= lastLogIndex)) {
reply.VoteGranted = true
rf.votedFor = args.CandidateId
} else {
reply.VoteGranted = false
}
reply.Term = rf.currentTerm
}
// example code to send a RequestVote RPC to a server.
// server is the index of the target server in rf.peers[].
// expects RPC arguments in args.
// fills in *reply with RPC reply, so caller should
// pass &reply.
// the types of the args and reply passed to Call() must be
// the same as the types of the arguments declared in the
// handler function (including whether they are pointers).
//
// The labrpc package simulates a lossy network, in which servers
// may be unreachable, and in which requests and replies may be lost.
// Call() sends a request and waits for a reply. If a reply arrives
// within a timeout interval, Call() returns true; otherwise
// Call() returns false. Thus Call() may not return for a while.
// A false return can be caused by a dead server, a live server that
// can't be reached, a lost request, or a lost reply.
//
// Call() is guaranteed to return (perhaps after a delay) *except* if the
// handler function on the server side does not return.Thus there
// is no need to implement your own timeouts around Call().
//
// look at the comments in ../labrpc/labrpc.go for more details.
//
// if you're having trouble getting RPC to work, check that you've
// capitalized all field names in structs passed over RPC, and
// that the caller passes the address of the reply struct with &, not
// the struct itself.
func (rf *Raft) sendRequestVote(server int, args *RequestVoteArgs, reply *RequestVoteReply) bool {
ok := rf.peers.Call("Raft.RequestVote", args, reply)
return ok
}
// the service using Raft (e.g. a k/v server) wants to start
// agreement on the next command to be appended to Raft's log. if this
// server isn't the leader, returns false. otherwise start the
// agreement and return immediately. there is no guarantee that this
// command will ever be committed to the Raft log, since the leader
// may fail or lose an election. even if the Raft instance has been killed,
// this function should return gracefully.
//
// the first return value is the index that the command will appear at
// if it's ever committed. the second return value is the current
// term. the third return value is true if this server believes it is
// the leader.
func (rf *Raft) Start(command interface{}) (int, int, bool) {
index := -1
term := -1
isLeader := rf.state == "Leader"
// Your code here (3B).
if isLeader {
rf.mu.Lock()
index = len(rf.logs)
term = rf.currentTerm
log := Entry{Term: term, Command: command, Index: len(rf.logs)}
rf.logs = append(rf.logs, log)
rf.mu.Unlock()
}
return index, term, isLeader
}
// the tester doesn't halt goroutines created by Raft after each test,
// but it does call the Kill() method. your code can use killed() to
// check whether Kill() has been called. the use of atomic avoids the
// need for a lock.
//
// the issue is that long-running goroutines use memory and may chew
// up CPU time, perhaps causing later tests to fail and generating
// confusing debug output. any goroutine with a long-running loop
// should call killed() to check whether it should stop.
func (rf *Raft) Kill() {
atomic.StoreInt32(&rf.dead, 1)
// Your code here, if desired.
}
func (rf *Raft) killed() bool {
z := atomic.LoadInt32(&rf.dead)
return z == 1
}
func (rf *Raft) initLeaderState() {
rf.nextIndex = make([]int, len(rf.peers))
rf.matchIndex = make([]int, len(rf.peers))
for i := range rf.peers {
rf.nextIndex = len(rf.logs)
rf.matchIndex = 0
}
}
func (rf *Raft) startElement() {
rf.mu.Lock()
rf.state = "Candidate"
rf.currentTerm++
rf.voteCount = 1
rf.votedFor = rf.me
rf.lastLeaderCheck = time.Now()
rf.mu.Unlock()
var wg sync.WaitGroup
for i := range rf.peers {
if i != rf.me {
wg.Add(1)
go func(i int) {
defer wg.Done()
if rf.state == "Candidate" {
args := &RequestVoteArgs{Term: rf.currentTerm, CandidateId: rf.me}
if len(rf.logs) > 0 {
args.LastLogIndex = len(rf.logs) - 1
args.LastLogTerm = rf.logs.Term
}
reply := &RequestVoteReply{}
if rf.sendRequestVote(i, args, reply) {
rf.mu.Lock()
if reply.Term > rf.currentTerm {
rf.state = "Follower"
rf.currentTerm = reply.Term
rf.voteCount = 0
rf.votedFor = -1
} else if reply.VoteGranted {
rf.voteCount++
if rf.voteCount >= (len(rf.peers)/2) && rf.state == "Candidate" {
rf.state = "Leader"
rf.initLeaderState()
go rf.sendAppendEntries()
}
}
rf.mu.Unlock()
}
}
}(i)
}
}
wg.Wait()
}
func (rf *Raft) ticker() {
rd := rand.New(rand.NewSource(int64(rf.me)))
for rf.killed() == false {
// Your code here (3A)
// Check if a leader election should be started.
if rf.state == "Leader" {
rf.lastLeaderCheck = time.Now()
continue
}
ms := rd.Int63n(300)
if time.Since(rf.lastLeaderCheck) > time.Duration(500+ms)*time.Millisecond || rf.state == "Candidate" {
rf.startElement()
}
// pause for a random amount of time between 50 and 350
// milliseconds.
ms = 50 + (rand.Int63() % 300)
time.Sleep(time.Duration(ms) * time.Millisecond)
}
}
func min(a, b int) int {
if a < b {
return a
}
return b
}
func (rf *Raft) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesReply) {
rf.mu.Lock()
defer rf.mu.Unlock()
rf.lastLeaderCheck = time.Now()
if args.Term < rf.currentTerm {
reply.Term = rf.currentTerm
reply.Success = false
return
}
if args.Term > rf.currentTerm {
rf.currentTerm = args.Term
rf.state = "Follower"
rf.votedFor = -1
}
//DPrintf("AppendEntries:term=%d,me=%d,args.Term=%d,logs=%v,newlogs=%v,preind=%v,preterm=%v,state=%v", rf.currentTerm, rf.me, args.Term, rf.logs, args.Logs, args.PrevLogIndex, args.PrevLogTerm, rf.state)
if args.PrevLogIndex > len(rf.logs)-1 || rf.logs.Term != args.PrevLogTerm {
reply.Term = rf.currentTerm
reply.Success = false
return
}
if len(args.Logs) != 0 && len(rf.logs) > args.PrevLogIndex+1 && rf.logs.Term != args.PrevLogTerm {
rf.logs = rf.logs[:args.PrevLogIndex+1]
}
if rf.me != args.LeaderId {
rf.logs = append(rf.logs, args.Logs...)
}
if args.LeaderCommit > rf.commitIndex {
rf.commitIndex = min(args.LeaderCommit, len(rf.logs)-1)
rf.applyLogs()
}
reply.Term = rf.currentTerm
reply.Success = true
//DPrintf("AppendEntries:state:%v,term=%d,me=%d,args.Term=%d", rf.state, rf.currentTerm, rf.me, args.Term)
}
func (rf *Raft) applyLogs() {
for rf.lastApplied < rf.commitIndex {
rf.lastApplied++
msg := ApplyMsg{
CommandValid: true,
Command: rf.logs.Command,
CommandIndex: rf.lastApplied,
}
rf.applyCh <- msg
}
}
func (rf *Raft) updateCommitIndex() {
for n := len(rf.logs) - 1; n > rf.commitIndex; n-- {
count := 1
for i := range rf.peers {
if i != rf.me && rf.matchIndex >= n && rf.logs.Term == rf.currentTerm {
count++
}
}
if count > len(rf.peers)/2 {
rf.commitIndex = n
rf.applyLogs()
break
}
}
}
func (rf *Raft) sendAppendEntries() {
for rf.killed() == false {
if rf.state == "Leader" {
var wg sync.WaitGroup
for i := range rf.peers {
wg.Add(1)
go func(i int) {
defer wg.Done()
rf.mu.Lock()
if rf.state != "Leader" {
rf.mu.Unlock()
return
}
args := &AppendEntriesArgs{Term: rf.currentTerm, LeaderId: rf.me, LeaderCommit: rf.commitIndex, PrevLogIndex: rf.matchIndex, PrevLogTerm: rf.logs].Term}
if rf.nextIndex < len(rf.logs) {
args.Logs = rf.logs:]
} else {
args.Logs = make([]Entry, 0)
}
rf.mu.Unlock()
reply := &AppendEntriesReply{}
ok := rf.peers.Call("Raft.AppendEntries", args, reply)
rf.mu.Lock()
if ok {
if reply.Success {
rf.nextIndex += len(args.Logs)
rf.matchIndex = rf.nextIndex - 1
rf.updateCommitIndex()
} else {
if reply.Term > rf.currentTerm {
rf.state = "Follower"
rf.votedFor = -1
rf.currentTerm = reply.Term
rf.lastLeaderCheck = time.Now()
} else if reply.Term == rf.currentTerm && rf.state == "Leader" && rf.nextIndex > 0 {
rf.nextIndex--
}
}
}
rf.mu.Unlock()
}(i)
}
wg.Wait()
} else {
return
}
ms := 100 + (rand.Int63() % 20)
time.Sleep(time.Duration(ms) * time.Millisecond)
}
}
// the service or tester wants to create a Raft server. the ports
// of all the Raft servers (including this one) are in peers[]. this
// server's port is peers. all the servers' peers[] arrays
// have the same order. persister is a place for this server to
// save its persistent state, and also initially holds the most
// recent saved state, if any. applyCh is a channel on which the
// tester or service expects Raft to send ApplyMsg messages.
// Make() must return quickly, so it should start goroutines
// for any long-running work.
func Make(peers []*labrpc.ClientEnd, me int, persister *Persister, applyCh chan ApplyMsg) *Raft {
rf := &Raft{}
rf.peers = peers
rf.persister = persister
rf.me = me
// Your initialization code here (3A, 3B, 3C).
rf.state = "Follower"
rf.applyCh = applyCh
rf.nextIndex = make([]int, len(peers))
for i := range rf.nextIndex {
rf.nextIndex = 1
}
rf.logs = make([]Entry, 0)
rf.logs = append(rf.logs, Entry{Term: 0})
// initialize from state persisted before a crash
rf.readPersist(persister.ReadRaftState())
// start ticker goroutine to start elections
go rf.ticker()
return rf
}
本帖最后由 923590810 于 2024-8-5 22:23 编辑
在实现Raft算法的日志复制部分时，可能会遇到各种问题。以下是一些常见的改进点和建议：
### 1. 确保正确的锁机制
确保在访问共享状态时正确使用锁，以防止数据竞争和不一致。
### 2. 确保`AppendEntries`的正确性
检查`AppendEntries`的实现，确保它正确处理了各种情况，包括日志不一致的情况。
### 3. 确保日志条目正确追加
确保在追加日志条目时，正确处理了日志冲突和覆盖。
### 4. 确保提交索引正确更新
确保在日志条目复制到多数服务器后，正确更新提交索引并应用日志条目。
### 5. 确保心跳机制正常工作
确保领导者定期发送心跳（空的`AppendEntries`）来保持领导者地位。
### 详细检查代码的几个关键部分：
#### 1. `AppendEntries`函数
确保`AppendEntries`函数正确处理了各种情况，包括日志不一致、日志追加和提交索引更新。
```go
func (rf *Raft) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesReply) {
rf.mu.Lock()
defer rf.mu.Unlock()
rf.lastLeaderCheck = time.Now()
if args.Term < rf.currentTerm {
reply.Term = rf.currentTerm
reply.Success = false
return
}
if args.Term > rf.currentTerm {
rf.currentTerm = args.Term
rf.state = "Follower"
rf.votedFor = -1
}
// 检查前一个日志条目是否匹配
if args.PrevLogIndex >= len(rf.logs) || rf.logs.Term != args.PrevLogTerm {
reply.Term = rf.currentTerm
reply.Success = false
return
}
// 追加新日志条目
rf.logs = append(rf.logs[:args.PrevLogIndex+1], args.Logs...)
// 更新提交索引
if args.LeaderCommit > rf.commitIndex {
rf.commitIndex = min(args.LeaderCommit, len(rf.logs)-1)
rf.applyLogs()
}
reply.Term = rf.currentTerm
reply.Success = true
}
```
#### 2. `sendAppendEntries`函数
确保领导者定期发送`AppendEntries` RPC，并正确处理回复。
```go
func (rf *Raft) sendAppendEntries() {
for rf.killed() == false {
if rf.state == "Leader" {
var wg sync.WaitGroup
for i := range rf.peers {
if i != rf.me {
wg.Add(1)
go func(i int) {
defer wg.Done()
rf.mu.Lock()
if rf.state != "Leader" {
rf.mu.Unlock()
return
}
prevLogIndex := rf.nextIndex - 1
prevLogTerm := rf.logs.Term
entries := make([]Entry, len(rf.logs))
copy(entries, rf.logs)
args := &AppendEntriesArgs{
Term: rf.currentTerm,
LeaderId: rf.me,
PrevLogIndex: prevLogIndex,
PrevLogTerm:prevLogTerm,
Logs: entries,
LeaderCommit: rf.commitIndex,
}
rf.mu.Unlock()
reply := &AppendEntriesReply{}
ok := rf.peers.Call("Raft.AppendEntries", args, reply)
rf.mu.Lock()
if ok {
if reply.Success {
rf.nextIndex = prevLogIndex + len(entries) + 1
rf.matchIndex = rf.nextIndex - 1
rf.updateCommitIndex()
} else {
if reply.Term > rf.currentTerm {
rf.state = "Follower"
rf.currentTerm = reply.Term
rf.votedFor = -1
} else {
rf.nextIndex = max(1, rf.nextIndex-1)
}
}
}
rf.mu.Unlock()
}(i)
}
}
wg.Wait()
}
ms := 100 + (rand.Int63() % 20)
time.Sleep(time.Duration(ms) * time.Millisecond)
}
}
```
#### 3. `updateCommitIndex`函数
确保在多数服务器复制日志条目后，正确更新提交索引。
```go
func (rf *Raft) updateCommitIndex() {
for n := len(rf.logs) - 1; n > rf.commitIndex; n-- {
count := 1
for i := range rf.peers {
if i != rf.me && rf.matchIndex >= n && rf.logs.Term == rf.currentTerm {
count++
}
}
if count > len(rf.peers)/2 {
rf.commitIndex = n
rf.applyLogs()
break
}
}
}
```
### 其他注意事项
- **日志压缩和快照**：如果日志条目过多，可能需要实现日志压缩和快照功能，以减少日志大小和提高效率。
- **网络分区处理**：确保在网络分区恢复后，日志能够正确同步和一致。
通过检查和改进上述关键部分，可以提高日志复制功能的正确性和鲁棒性，确保通过测试。GPT-4o给你的回答
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