芜湖做网站的客户关于seo的行业岗位有哪些

前言

redis的核心是数据的快速存储，下面就来分析一下godis的底层存储是如何实现，先分析单机服务。

此文采用抓大放小原则，先大的流程方向，再抓细节。

流程图

源码分析

现在以客户端连接，并发起set key val命令为例子
在单机部署的时候，服务启动，会创建一个处理实例，并创建一个单机的db

// redis/server.go
// 创建一个处理实例
// MakeHandler creates a Handler instance
func MakeHandler() *Handler {// redis的一个存储引擎var db database.DB// 创建是集群还是单例if config.Properties.ClusterEnable {db = cluster.MakeCluster()} else {db = database2.NewStandaloneServer()}return &Handler{db: db,}
}

有客户端连接，会生成一个异步方法处理每个客户端，一旦有客户端的消息，都会进入Handle方法。

// redis/server/server.go
// 处理接收到客户端的命令
// Handle receives and executes redis commands
func (h *Handler) Handle(ctx context.Context, conn net.Conn) {if h.closing.Get() {// closing handler refuse new connection_ = conn.Close()return}client := connection.NewConn(conn)// 存储一个客户端h.activeConn.Store(client, struct{}{})// 获取字符串ch := parser.ParseStream(conn)// 接收客户端数据for payload := range ch {// 遍历消息体// ......... 经过各种校验// 获取到客户端信息r, ok := payload.Data.(*protocol.MultiBulkReply)if !ok {logger.Error("require multi bulk protocol")continue}// 执行结果result := h.db.Exec(client, r.Args)// 结果回复if result != nil {_, _ = client.Write(result.ToBytes())} else {_, _ = client.Write(unknownErrReplyBytes)}}
}

客户端的各种命令进行判断，set是属于正常的数据操作命令，直接通过判断，获取数据库，并在当前数据库中执行

// database/server.go
func (server *Server) Exec(c redis.Connection, cmdLine [][]byte) (result redis.Reply) {defer func() {if err := recover(); err != nil {logger.Warn(fmt.Sprintf("error occurs: %v\n%s", err, string(debug.Stack())))result = &protocol.UnknownErrReply{}}}()cmdName := strings.ToLower(string(cmdLine[0]))// pingif cmdName == "ping" {return Ping(c, cmdLine[1:])}// authenticateif cmdName == "auth" {return Auth(c, cmdLine[1:])}// ........// 各种各样的判断，暂时不管// 获取当前的数据索引// normal commandsdbIndex := c.GetDBIndex()// 获取当前数据库selectedDB, errReply := server.selectDB(dbIndex)if errReply != nil {return errReply}// 以当前数据库，执行命令return selectedDB.Exec(c, cmdLine)
}

命令名称解析出来后，从cmdTable获取对应的执行方法，如prepare、executor

// Exec executes command within one database
func (db *DB) Exec(c redis.Connection, cmdLine [][]byte) redis.Reply {// transaction control commands and other commands which cannot execute within transactioncmdName := strings.ToLower(string(cmdLine[0]))// ...return db.execNormalCommand(cmdLine)
}func (db *DB) execNormalCommand(cmdLine [][]byte) redis.Reply {// 获取到正常的执行命令cmdName := strings.ToLower(string(cmdLine[0]))// 获取到commondcmd, ok := cmdTable[cmdName]if !ok {return protocol.MakeErrReply("ERR unknown command '" + cmdName + "'")}if !validateArity(cmd.arity, cmdLine) {return protocol.MakeArgNumErrReply(cmdName)}prepare := cmd.preparewrite, read := prepare(cmdLine[1:])db.addVersion(write...)// 数据库上锁db.RWLocks(write, read)// 命令执行完后解锁defer db.RWUnLocks(write, read)// 执行命令方法fun := cmd.executorreturn fun(db, cmdLine[1:])
}

set命令对应的方法，从代码可以发现，其实数据是存储在定义的map结构的集合中，自此，命令已经执行完毕，返回执行结果。

func execSet(db *DB, args [][]byte) redis.Reply {// 提取keykey := string(args[0])// 提取valvalue := args[1]// 提取策略policy := upsertPolicy// 提取过期时间ttl := unlimitedTTL// parse options// 如何参数大于2个，说明有其他参数，需要做其他处理// .....entity := &database.DataEntity{Data: value,}var result int// 更新策略switch policy {case upsertPolicy:// 默认策略db.PutEntity(key, entity)result = 1case insertPolicy:result = db.PutIfAbsent(key, entity)case updatePolicy:result = db.PutIfExists(key, entity)}if result > 0 {if ttl != unlimitedTTL {expireTime := time.Now().Add(time.Duration(ttl) * time.Millisecond)// 设置过期时间db.Expire(key, expireTime)db.addAof(CmdLine{[]byte("SET"),args[0],args[1],})db.addAof(aof.MakeExpireCmd(key, expireTime).Args)} else {db.Persist(key) // override ttldb.addAof(utils.ToCmdLine3("set", args...))}}if result > 0 {return &protocol.OkReply{}}return &protocol.NullBulkReply{}
}// database.go
// 将数据放入DB
// PutEntity a DataEntity into DB
func (db *DB) PutEntity(key string, entity *database.DataEntity) int {// 当前数据库的数据字段ret := db.data.PutWithLock(key, entity)// db.insertCallback may be set as nil, during `if` and actually callback// so introduce a local variable `cb`if cb := db.insertCallback; ret > 0 && cb != nil {cb(db.index, key, entity)}return ret
}// datastruct/dict/concurrent.go
// ConcurrentDict is thread safe map using sharding lock
// 这里可以看出，数据其实就是存在map集合里面
type ConcurrentDict struct {table      []*shardcount      int32shardCount int
}type shard struct {m     map[string]interface{}mutex sync.RWMutex
}// datastruct/dict/concurrent.go
func (dict *ConcurrentDict) PutWithLock(key string, val interface{}) (result int) {if dict == nil {panic("dict is nil")}hashCode := fnv32(key)index := dict.spread(hashCode)s := dict.getShard(index)// 将数据放入map中if _, ok := s.m[key]; ok {s.m[key] = valreturn 0}dict.addCount()// 存储kv结构数据，完成s.m[key] = valreturn 1
}

其实还有一个问题，就是cmdTable怎么来的，为什么fun(db, cmdLine[1:])就完成了？

在router.go这个代码中，是生成一个新的cmdTable的map集合；registerCommand这个函数是将各种命令塞入cmdTable里面。每个数据结构如string等都有定义的方法。

main启动前都会调用init()，这个是golang特殊的函数，顺序按照文件的顺序执行。

这里就是在服务启动前，将所有命令注册到cmdTable集合。

// database/router.go
// 命令集
var cmdTable = make(map[string]*command)
// ....
// 注册命令，将命令存放在cmdTable集合里面
// registerCommand registers a normal command, which only read or modify a limited number of keys
func registerCommand(name string, executor ExecFunc, prepare PreFunc, rollback UndoFunc, arity int, flags int) *command {name = strings.ToLower(name)cmd := &command{name:     name,executor: executor,prepare:  prepare,undo:     rollback,arity:    arity,flags:    flags,}cmdTable[name] = cmdreturn cmd
}//========================================// database/string.gofunc execSet(db *DB, args [][]byte) redis.Reply {
//....
}// execSetNX sets string if not exists
func execSetNX(db *DB, args [][]byte) redis.Reply {// .....
}// execSetEX sets string and its ttl
func execSetEX(db *DB, args [][]byte) redis.Reply {// ...
}func init() {// 调用注册命令函数，注册方法，如Set则是执行execSet方法registerCommand("Set", execSet, writeFirstKey, rollbackFirstKey, -3, flagWrite).attachCommandExtra([]string{redisFlagWrite, redisFlagDenyOOM}, 1, 1, 1)registerCommand("SetNx", execSetNX, writeFirstKey, rollbackFirstKey, 3, flagWrite).attachCommandExtra([]string{redisFlagWrite, redisFlagDenyOOM, redisFlagFast}, 1, 1, 1)registerCommand("SetEX", execSetEX, writeFirstKey, rollbackFirstKey, 4, flagWrite).attachCommandExtra([]string{redisFlagWrite, redisFlagDenyOOM}, 1, 1, 1)// .....
}

ExecFunc是规范方法，每个命令对应的执行都按照规范定义。

// database/router.gotype command struct {// 命令名称name     string// 执行方法executor ExecFunc// prepare returns related keys commandprepare PreFunc// undo generates undo-log before command actually executed, in case the command needs to be rolled backundo UndoFunc// arity means allowed number of cmdArgs, arity < 0 means len(args) >= -arity.// for example: the arity of `get` is 2, `mget` is -2arity intflags intextra *commandExtra
}// ========================================// database/database.go
// 执行方法接口
// ExecFunc is interface for command executor
// args don't include cmd line
type ExecFunc func(db *DB, args [][]byte) redis.Reply