文件一致性的一些笔记

原创
INodeFileUnderConstruction 继承自INodeFile ，但是多了下面这六个类变量。都是在为了标示UnderConstruction状态时的一些必要的信息
class INodeFileUnderConstruction extends INodeFile

String clientName;         // lease holder
  private final String clientMachine;
  private final DatanodeDescriptor clientNode; // if client is a cluster node too.

  private int primaryNodeIndex = -1; //the node working on lease recovery
  private DatanodeDescriptor[] targets = null;   //locations for last block
  private long lastRecoveryTime = 0;