Hadoop学习二十九：Hadoop-hdfs NameNode源码 成员变量

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一. NameNode概述

 * The NameNode controls two critical tables:
 *   1)  filename->blocksequence (namespace)
 *   2)  block->machinelist ("inodes")
 *
 * The first table is stored on disk and is very precious.
 * The second table is rebuilt every time the NameNode comes
 * up.

1. 上面这段其实就和FSNameSystem作用一样，因为NameNode的功能基本就是靠FSNameSystem实现的。
2. 当然，同DataNode一样，NameNode也是一个RPC Server。
3. NameNode也要提供Http服务。

二. NameNode成员变量

 

  //一个文件系统  一个NameNode 一个FSNamesystem 一个FSDirectory
  public FSNamesystem namesystem; // TODO: This should private. Use getNamesystem() instead. 
  //BackupNode, Datanodes and all other services与serviceRpcServer通信
  private Server serviceRpcServer;
  //Clients 与server通信
  private Server server;
  
  //serviceRpcServer ip port
  protected InetSocketAddress serviceRPCAddress = null;
  //server ip port
  private InetSocketAddress serverAddress = null;
  
  //NameNode可以提供http服务
  private HttpServer httpServer;
  //http服务 ip port
  private InetSocketAddress httpAddress = null;
  
  //暂时不知道做什么  后面看把
  private Thread emptier;