hdfs datanode 启动流程中关于拉取namenode信

hfds datanode 启动组件

hfds datanode 启动流程

注册心跳

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BPOfferService.java

 /**
   * Called by the BPServiceActors when they handshake to a NN.
   * If this is the first NN connection, this sets the namespace info
   * for this BPOfferService. If it's a connection to a new NN, it
   * verifies that this namespace matches (eg to prevent a misconfiguration
   * where a StandbyNode from a different cluster is specified)
   *
   * 两个namenode:
   *  hadoop1  -> actor1 => bpnsInfo
   *  hadoop2  -> actor2 => bpnsInfo
   *
   */
  void verifyAndSetNamespaceInfo(NamespaceInfo nsInfo) throws IOException {
    writeLock();
    try {
      //actor1
      //actor2
      if (this.bpNSInfo == null) {
        //赋值
        this.bpNSInfo = nsInfo;
        boolean success = false;

        // Now that we know the namespace ID, etc, we can pass this to the DN.
        // The DN can now initialize its local storage if we are the
        // first BP to handshake, etc.
        try {
          dn.initBlockPool(this);
          success = true;
        } finally {
          if (!success) {
            // The datanode failed to initialize the BP. We need to reset
            // the namespace info so that other BPService actors still have
            // a chance to set it, and re-initialize the datanode.
            this.bpNSInfo = null;
          }
        }
      } else {
        /**
         * datanode注册的时候 就会通过namenode获取集群的一些信息
         */

        //所以如果代码能走到这儿说明，我们的BlockPoolId肯定已经获取到了
        checkNSEquality(bpNSInfo.getBlockPoolID(), nsInfo.getBlockPoolID(),
            "Blockpool ID");
        checkNSEquality(bpNSInfo.getNamespaceID(), nsInfo.getNamespaceID(),
            "Namespace ID");
        checkNSEquality(bpNSInfo.getClusterID(), nsInfo.getClusterID(),
            "Cluster ID");


//        //如果代码执行到这儿，说明不仅两个namenode上都获取到了信息，而且两个namenode的信息都对上了。
//        if(blockPoolID == null){
//          this.blockPoolID = bpNSInfo.getBlockPoolID();
//        }

      }
    } finally {
      writeUnlock();
    }
  }

总结

可以发现，datanode通过BPServiceActors和namenode建立连接，并初始化过程中会校验Blockpool ID，Namespace ID，Cluster ID，这几个至关重要，为下文恢复集群做准备。