## 三 ZooKeeper基本数据模型

### 3.1 基本数据模型介绍

- zk的数据模型也可以理解为linux/unix的文件目录: /usr/local/...

- 每一个节点都称之为znode, 它可以有子节点, 也可以有数据

- 每个节点分为临时节点和永久节点,临时节点在客户端断开后消失

- 每一个zk节点都有各自的版本号, 可以通过命令行来显示节点信息

- 每当节点数据发生变化, 那么该节点的版本号会累加

- 删除/修改过时节点, 版本号不匹配会报错

- 每个zk节点存储的数据不宜过大, 几k即可

- 节点可以设置权限acl, 可以通过权限来限制用户的访问


### 3.2 ZooKeeper数据模型的基本操作

- 客户端连接

  - $ZOOKEEPER_HOME/bin 运行zkServer.sh start 开启zookeeper

  - 进入客户端

    ```shell
    ./zkCli.sh
    
    2018-12-29 02:23:22,904 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1235] - Session establishment complete on server localhost/0:0:0:0:0:0:0:1:2181, sessionid = 0x167f60ba5ea0002, negotiated timeout = 30000
    
    WATCHER::
    
    WatchedEvent state:SyncConnected type:None path:null
    [zk: localhost:2181(CONNECTED) 0]
    ```

    - ls 列出目录 help 查看帮助

    ``` shell
    WatchedEvent state:SyncConnected type:None path:null
    [zk: localhost:2181(CONNECTED) 0] ls /
    [zookeeper]
    [zk: localhost:2181(CONNECTED) 1] ls /zookeeper
    [quota]
    [zk: localhost:2181(CONNECTED) 2] ls /zookeeper/quota
    []
    [zk: localhost:2181(CONNECTED) 3] help
    ZooKeeper -server host:port cmd args
            stat path [watch]
            set path data [version]
            ls path [watch]
            delquota [-n|-b] path
            ls2 path [watch]
            setAcl path acl
            setquota -n|-b val path
            history
            redo cmdno
            printwatches on|off
            delete path [version]
            sync path
            listquota path
            rmr path
            get path [watch]
            create [-s] [-e] path data acl
            addauth scheme auth
            quit
            getAcl path
            close
            connect host:port
    
    ```

- 查看znode结构

  - ls 列出目录 help 查看帮助

    ``` shell
    WatchedEvent state:SyncConnected type:None path:null
    [zk: localhost:2181(CONNECTED) 0] ls /
    [zookeeper]
    [zk: localhost:2181(CONNECTED) 1] ls /zookeeper
    [quota]
    [zk: localhost:2181(CONNECTED) 2] ls /zookeeper/quota
    []
    [zk: localhost:2181(CONNECTED) 3] help
    ZooKeeper -server host:port cmd args
            stat path [watch]
            set path data [version]
            ls path [watch]
            delquota [-n|-b] path
            ls2 path [watch]
            setAcl path acl
            setquota -n|-b val path
            history
            redo cmdno
            printwatches on|off
            delete path [version]
            sync path
            listquota path
            rmr path
            get path [watch]
            create [-s] [-e] path data acl
            addauth scheme auth
            quit
            getAcl path
            close
            connect host:port
    ```

- 关闭客户端连接 ctrl+c