• 采用一致性hash算法将key分散到不同的节点，客户端可以连接到集群中任意一个节点
• https://github.com/csgopher/go-redis
• 本文涉及以下文件：
  consistenthash：实现添加和选择节点方法
  standalone_database：单机database
  client：客户端
  client_pool：实现连接池
  cluster_database：对key进行路由
  com：与其他节点通信
  router，ping，keys，del，select：各类命令的转发具体逻辑
  
  

一致性哈希

为什么需要一致性 hash？
在采用分片方式建立分布式缓存时，我们面临的第一个问题是如何决定存储数据的节点。最自然的方式是参考 hash 表的做法，假设集群中存在 n 个节点，我们用 node = hashCode(key) % n 来决定所属的节点。
普通 hash 算法解决了如何选择节点的问题，但在分布式系统中经常出现增加节点或某个节点宕机的情况。若节点数 n 发生变化, 大多数 key 根据 node = hashCode(key) % n 计算出的节点都会改变。这意味着若要在 n 变化后维持系统正常运转，需要将大多数数据在节点间进行重新分布。这个操作会消耗大量的时间和带宽等资源，这在生产环境下是不可接受的。
算法原理
一致性 hash 算法的目的是在节点数量 n 变化时, 使尽可能少的 key 需要进行节点间重新分布。一致性 hash 算法将数据 key 和服务器地址 addr 散列到 2^32 的空间中。
我们将 2^32 个整数首尾相连形成一个环，首先计算服务器地址 addr 的 hash 值放置在环上。然后计算 key 的 hash 值放置在环上，顺时针查找，将数据放在找到的的第一个节点上。
在增加或删除节点时只有该节点附近的数据需要重新分布，从而解决了上述问题。
如果服务器节点较少则比较容易出现数据分布不均匀的问题，一般来说环上的节点越多数据分布越均匀。我们不需要真的增加一台服务器，只需要将实际的服务器节点映射为几个虚拟节点放在环上即可。
参考：https://www.cnblogs.com/Finley/p/14038398.html

lib/consistenthash/consistenthash.go

type HashFunc func(data []byte) uint32
type NodeMap struct {
   hashFunc    HashFunc
   nodeHashs   []int          
   nodehashMap map[int]string 
}
func NewNodeMap(fn HashFunc) *NodeMap {
   m := &NodeMap{
      hashFunc:    fn,
      nodehashMap: make(map[int]string),
   }
   if m.hashFunc == nil {
      m.hashFunc = crc32.ChecksumIEEE
   }
   return m
}
func (m *NodeMap) IsEmpty() bool {
   return len(m.nodeHashs) == 0
}
func (m *NodeMap) AddNode(keys ...string) {
   for _, key := range keys {
      if key == "" {
         continue
      }
      hash := int(m.hashFunc([]byte(key)))
      m.nodeHashs = append(m.nodeHashs, hash)
      m.nodehashMap[hash] = key
   }
   sort.Ints(m.nodeHashs)
}
func (m *NodeMap) PickNode(key string) string {
   if m.IsEmpty() {
      return ""
   }
   hash := int(m.hashFunc([]byte(key)))
   
   idx := sort.Search(len(m.nodeHashs), func(i int) bool {
      return m.nodeHashs[i] >= hash
   })
   
   if idx == len(m.nodeHashs) {
      idx = 0
   }
   return m.nodehashMap[m.nodeHashs[idx]]
}

HashFunc：hash函数定义，Go的hash函数就是这样定义的
NodeMap：存储所有节点和节点的hash

• nodeHashs：各个节点的hash值，顺序的
• nodehashMap<hash, 节点>

AddNode：添加节点到一致性哈希中
PickNode：选择节点。使用二分查找，如果hash比nodeHashs中最大的hash还要大，idx=0

database/standalone_database.go

type StandaloneDatabase struct {
   dbSet []*DB
   aofHandler *aof.AofHandler
}
func NewStandaloneDatabase() *StandaloneDatabase {
  ......
}

把database/database改名为database/standalone_database，再增加一个cluster_database用于对key的路由

resp/client/client.go

// Client is a pipeline mode redis client
type Client struct {
   conn        net.Conn
   pendingReqs chan *request // wait to send
   waitingReqs chan *request // waiting response
   ticker      *time.Ticker
   addr        string
   working *sync.WaitGroup // its counter presents unfinished requests(pending and waiting)
}
// request is a message sends to redis server
type request struct {
   id        uint64
   args      [][]byte
   reply     resp.Reply
   heartbeat bool
   waiting   *wait.Wait
   err       error
}
const (
   chanSize = 256
   maxWait  = 3 * time.Second
)
// MakeClient creates a new client
func MakeClient(addr string) (*Client, error) {
   conn, err := net.Dial("tcp", addr)
   if err != nil {
      return nil, err
   }
   return &Client{
      addr:        addr,
      conn:        conn,
      pendingReqs: make(chan *request, chanSize),
      waitingReqs: make(chan *request, chanSize),
      working:     &sync.WaitGroup{},
   }, nil
}
// Start starts asynchronous goroutines
func (client *Client) Start() {
   client.ticker = time.NewTicker(10 * time.Second)
   go client.handleWrite()
   go func() {
      err := client.handleRead()
      if err != nil {
         logger.Error(err)
      }
   }()
   go client.heartbeat()
}
// Close stops asynchronous goroutines and close connection
func (client *Client) Close() {
   client.ticker.Stop()
   // stop new request
   close(client.pendingReqs)
   // wait stop process
   client.working.Wait()
   // clean
   _ = client.conn.Close()
   close(client.waitingReqs)
}
func (client *Client) handleConnectionError(err error) error {
   err1 := client.conn.Close()
   if err1 != nil {
      if opErr, ok := err1.(*net.OpError); ok {
         if opErr.Err.Error() != "use of closed network connection" {
            return err1
         }
      } else {
         return err1
      }
   }
   conn, err1 := net.Dial("tcp", client.addr)
   if err1 != nil {
      logger.Error(err1)
      return err1
   }
   client.conn = conn
   go func() {
      _ = client.handleRead()
   }()
   return nil
}
func (client *Client) heartbeat() {
   for range client.ticker.C {
      client.doHeartbeat()
   }
}
func (client *Client) handleWrite() {
   for req := range client.pendingReqs {
      client.doRequest(req)
   }
}
// Send sends a request to redis server
func (client *Client) Send(args [][]byte) resp.Reply {
   request := &request{
      args:      args,
      heartbeat: false,
      waiting:   &wait.Wait{},
   }
   request.waiting.Add(1)
   client.working.Add(1)
   defer client.working.Done()
   client.pendingReqs <- request
   timeout := request.waiting.WaitWithTimeout(maxWait)
   if timeout {
      return reply.MakeErrReply("server time out")
   }
   if request.err != nil {
      return reply.MakeErrReply("request failed")
   }
   return request.reply
}
func (client *Client) doHeartbeat() {
   request := &request{
      args:      [][]byte{[]byte("PING")},
      heartbeat: true,
      waiting:   &wait.Wait{},
   }
   request.waiting.Add(1)
   client.working.Add(1)
   defer client.working.Done()
   client.pendingReqs <- request
   request.waiting.WaitWithTimeout(maxWait)
}
func (client *Client) doRequest(req *request) {
   if req == nil || len(req.args) == 0 {
      return
   }
   re := reply.MakeMultiBulkReply(req.args)
   bytes := re.ToBytes()
   _, err := client.conn.Write(bytes)
   i := 0
   for err != nil && i < 3 {
      err = client.handleConnectionError(err)
      if err == nil {
         _, err = client.conn.Write(bytes)
      }
      i++
   }
   if err == nil {
      client.waitingReqs <- req
   } else {
      req.err = err
      req.waiting.Done()
   }
}
func (client *Client) finishRequest(reply resp.Reply) {
   defer func() {
      if err := recover(); err != nil {
         debug.PrintStack()
         logger.Error(err)
      }
   }()
   request := <-client.waitingReqs
   if request == nil {
      return
   }
   request.reply = reply
   if request.waiting != nil {
      request.waiting.Done()
   }
}
func (client *Client) handleRead() error {
   ch := parser.ParseStream(client.conn)
   for payload := range ch {
      if payload.Err != nil {
         client.finishRequest(reply.MakeErrReply(payload.Err.Error()))
         continue
      }
      client.finishRequest(payload.Data)
   }
   return nil
}

client：Redis客户端，具体看：https://www.cnblogs.com/Finley/p/14028402.html

go.mod

require github.com/jolestar/go-commons-pool/v2 v2.1.2

key的转发需要当前节点存储其他节点的连接，互相作为客户端，使用连接池将其他连接池化

cluster/client_pool.go

type connectionFactory struct {
   Peer string // 连接地址
}
func (f *connectionFactory) MakeObject(ctx context.Context) (*pool.PooledObject, error) {
   c, err := client.MakeClient(f.Peer)
   if err != nil {
      return nil, err
   }
   c.Start()
   return pool.NewPooledObject(c), nil
}
func (f *connectionFactory) DestroyObject(ctx context.Context, object *pool.PooledObject) error {
   c, ok := object.Object.(*client.Client)
   if !ok {
      return errors.New("type mismatch")
   }
   c.Close()
   return nil
}
func (f *connectionFactory) ValidateObject(ctx context.Context, object *pool.PooledObject) bool {
   // do validate
   return true
}
func (f *connectionFactory) ActivateObject(ctx context.Context, object *pool.PooledObject) error {
   // do activate
   return nil
}
func (f *connectionFactory) PassivateObject(ctx context.Context, object *pool.PooledObject) error {
   // do passivate
   return nil
}

client_pool：使用连接池的NewObjectPoolWithDefaultConfig创建连接，需要实现PooledObjectFactory接口

redis.conf

self 127.0.0.1:6379
peers 127.0.0.1:6380

配置中写自己和其他节点的地址

cluster/cluster_database.go

type clusterDatabase struct {
   self           string
   nodes          []string
   peerPicker     *consistenthash.NodeMap
   peerConnection map[string]*pool.ObjectPool
   db             databaseface.Database
}
func MakeClusterDatabase() *clusterDatabase {
   cluster := &clusterDatabase{
      self:           config.Properties.Self,
      db:             database.NewStandaloneDatabase(),
      peerPicker:     consistenthash.NewNodeMap(nil),
      peerConnection: make(map[string]*pool.ObjectPool),
   }
   nodes := make([]string, 0, len(config.Properties.Peers)+1)
   for _, peer := range config.Properties.Peers {
      nodes = append(nodes, peer)
   }
   nodes = append(nodes, config.Properties.Self)
   cluster.peerPicker.AddNode(nodes...)
   ctx := context.Background()
   for _, peer := range config.Properties.Peers {
      cluster.peerConnection[peer] = pool.NewObjectPoolWithDefaultConfig(ctx, &connectionFactory{
         Peer: peer,
      })
   }
   cluster.nodes = nodes
   return cluster
}
func (cluster *clusterDatabase) Close() {
	cluster.db.Close()
}
func (cluster *ClusterDatabase) AfterClientClose(c resp.Connection) {
	cluster.db.AfterClientClose(c)
}
type CmdFunc func(cluster *clusterDatabase, c resp.Connection, cmdAndArgs [][]byte) resp.Reply

cluster_database用于对key的路由
clusterDatabase：
nodes：所有节点
peerPicker ：节点的添加和选择
peerConnection：Map<node, 连接池>
db：单机database
CmdFunc：表示Redis的指令类型

cluster/com.go

func (cluster *clusterDatabase) getPeerClient(peer string) (*client.Client, error) {
   factory, ok := cluster.peerConnection[peer]
   if !ok {
      return nil, errors.New("connection factory not found")
   }
   raw, err := factory.BorrowObject(context.Background())
   if err != nil {
      return nil, err
   }
   conn, ok := raw.(*client.Client)
   if !ok {
      return nil, errors.New("connection factory make wrong type")
   }
   return conn, nil
}
func (cluster *clusterDatabase) returnPeerClient(peer string, peerClient *client.Client) error {
   connectionFactory, ok := cluster.peerConnection[peer]
   if !ok {
      return errors.New("connection factory not found")
   }
   return connectionFactory.ReturnObject(context.Background(), peerClient)
}
func (cluster *clusterDatabase) relay(peer string, c resp.Connection, args [][]byte) resp.Reply {
   if peer == cluster.self {
      return cluster.db.Exec(c, args)
   }
   peerClient, err := cluster.getPeerClient(peer)
   if err != nil {
      return reply.MakeErrReply(err.Error())
   }
   defer func() {
      _ = cluster.returnPeerClient(peer, peerClient)
   }()
   peerClient.Send(utils.ToCmdLine("SELECT", strconv.Itoa(c.GetDBIndex())))
   return peerClient.Send(args)
}
func (cluster *clusterDatabase) broadcast(c resp.Connection, args [][]byte) map[string]resp.Reply {
   result := make(map[string]resp.Reply)
   for _, node := range cluster.nodes {
      relay := cluster.relay(node, c, args)
      result[node] = relay
   }
   return result
}

communication：与其他节点通信。执行模式有本地（自己执行），转发（别人执行），群发（所有节点执行）
getPeerClient ：从连接池拿一个连接
returnPeerClient ：归还连接
relay ：转发指令给其他客户端，发送指令之前需要先发一下选择的db
broadcast ：指令广播给所有节点

cluster/router.go

func makeRouter() map[string]CmdFunc {
    routerMap := make(map[string]CmdFunc)
    routerMap["ping"] = ping
    routerMap["del"] = Del
    routerMap["exists"] = defaultFunc
    routerMap["type"] = defaultFunc
    routerMap["rename"] = Rename
    routerMap["renamenx"] = Rename
    routerMap["set"] = defaultFunc
    routerMap["setnx"] = defaultFunc
    routerMap["get"] = defaultFunc
    routerMap["getset"] = defaultFunc
    routerMap["flushdb"] = FlushDB
	routerMap["select"] = execSelect
    return routerMap
}
func defaultFunc(cluster *clusterDatabase, c resp.Connection, args [][]byte) resp.Reply {
    key := string(args[1])
    peer := cluster.peerPicker.PickNode(key)
    return cluster.relay(peer, c, args)
}

defaultFunc：转发指令的默认实现

cluster/ping.go

func ping(cluster *clusterDatabase, c resp.Connection, cmdAndArgs [][]byte) resp.Reply {
   return cluster.db.Exec(c, cmdAndArgs)
}

cluster/rename.go

func Rename(cluster *clusterDatabase, c resp.Connection, args [][]byte) resp.Reply {
   if len(args) != 3 {
      return reply.MakeErrReply("ERR wrong number of arguments for 'rename' command")
   }
   src := string(args[1])
   dest := string(args[2])
   srcPeer := cluster.peerPicker.PickNode(src)
   destPeer := cluster.peerPicker.PickNode(dest)
   if srcPeer != destPeer {
      return reply.MakeErrReply("ERR rename must within one slot in cluster mode")
   }
   return cluster.relay(srcPeer, c, args)
}

Rename：修改key的name，两个key的hash必须在同一个节点中

cluster/keys.go

func FlushDB(cluster *clusterDatabase, c resp.Connection, args [][]byte) resp.Reply {
   replies := cluster.broadcast(c, args)
   var errReply reply.ErrorReply
   for _, v := range replies {
      if reply.IsErrorReply(v) {
         errReply = v.(reply.ErrorReply)
         break
      }
   }
   if errReply == nil {
      return &reply.OkReply{}
   }
   return reply.MakeErrReply("error occurs: " + errReply.Error())
}

cluster/del.go

func Del(cluster *clusterDatabase, c resp.Connection, args [][]byte) resp.Reply {
   replies := cluster.broadcast(c, args)
   var errReply reply.ErrorReply
   var deleted int64 = 0
   for _, v := range replies {
      if reply.IsErrorReply(v) {
         errReply = v.(reply.ErrorReply)
         break
      }
      intReply, ok := v.(*reply.IntReply)
      if !ok {
         errReply = reply.MakeErrReply("error")
      }
      deleted += intReply.Code
   }
   if errReply == nil {
      return reply.MakeIntReply(deleted)
   }
   return reply.MakeErrReply("error occurs: " + errReply.Error())
}

cluster/select.go

func execSelect(cluster *clusterDatabase, c resp.Connection, cmdAndArgs [][]byte) resp.Reply {
   return cluster.db.Exec(c, cmdAndArgs)
}

cluster/cluster_database.go

var router = makeRouter()
func (cluster *clusterDatabase) Exec(c resp.Connection, cmdLine [][]byte) (result resp.Reply) {
   defer func() {
      if err := recover(); err != nil {
         logger.Warn(fmt.Sprintf("error occurs: %v\n%s", err, string(debug.Stack())))
         result = &reply.UnknownErrReply{}
      }
   }()
   cmdName := strings.ToLower(string(cmdLine[0]))
   cmdFunc, ok := router[cmdName]
   if !ok {
      return reply.MakeErrReply("ERR unknown command '" + cmdName + "', or not supported in cluster mode")
   }
   result = cmdFunc(cluster, c, cmdLine)
   return
}

resp/handler/handler.go

func MakeHandler() *RespHandler {
   var db databaseface.Database
   if config.Properties.Self != "" && len(config.Properties.Peers) > 0 {
      db = cluster.MakeClusterDatabase()
   } else {
      db = database.NewStandaloneDatabase()
   }
   return &RespHandler{
      db: db,
   }
}

MakeHandler：判断是单机还是集群

测试

先go build，打开项目文件夹找到exe文件，把exe文件和redis.conf放到一个文件夹里，redis.conf改成如下，然后启动exe文件。再回到GoLand启动第二个节点6379。

bind 0.0.0.0
port 6380
appendonly yes
appendfilename appendonly.aof
self 127.0.0.1:6380
peers 127.0.0.1:6379