Hadoop NameNode起動のロードFSImage(二)

前回は起動中にFSImageをロードする前の一連の検査を分析したが、今回はFSImageの本当のロード部分を見てみると、ここでこのファイルに対する読み取り操作が見られ、これらの操作によってこのファイルの構造、およびメモリの中の構造が知ることができ、個人的にHDFSは安全、回復の面での考慮から、起動中にかなりの検査をしたと感じている.しかし、このファイルを読むだけでは、流れは理解しやすいので、JAVAのファイルの読み書きに精通していれば、この関数は一目で大体分かります.クラスタには次のようなディレクトリがあります.
   HDFS://192.168.0.1:9000/a.txt
   HDFS://192.168.0.1:9000/test/b.txt
ファイルは全部で2つですが、統計ファイル数はルートディレクトリ、testディレクトリ、a.txt、b.txtの4つです
 FSImage.java

  boolean loadFSImage(File curFile) throws IOException {
    assert this.getLayoutVersion() < 0 : "Negative layout version is expected.";
    assert curFile != null : "curFile is null";
 
    FSNamesystem fsNamesys = FSNamesystem.getFSNamesystem();
    FSDirectory fsDir = fsNamesys.dir;
 
    //
    // Load in bits
    //
    boolean needToSave = true;
    //      ，     
    DataInputStream in = new DataInputStream(new BufferedInputStream(
                              new FileInputStream(curFile)));
    try {
      /*
       * Note: Remove any checks for versionearlier than
       * Storage.LAST_UPGRADABLE_LAYOUT_VERSIONsince we should never get
       * to here with older images.
       */
     
      /*
       * TODO we need to change format of the image file
       * it should not contain version and namespacefields
       */
      // read image version: first appeared in version -1
      //      ，        ，      ，             
      int imgVersion = in.readInt();
      // read namespaceID: first appeared in version -2
      this.namespaceID = in.readInt();
 
      // read number of files
      long numFiles;
      if (imgVersion <= -16) {
        numFiles = in.readLong();
      } else {
        numFiles = in.readInt();
      }
 
      this.layoutVersion = imgVersion;
      // read in the last generation stamp.
      if (imgVersion <= -12) {
        long genstamp = in.readLong();
        fsNamesys.setGenerationStamp(genstamp);
      }
 
      needToSave = (imgVersion != FSConstants.LAYOUT_VERSION);
 
      // read file info
      short replication = FSNamesystem.getFSNamesystem().getDefaultReplication();
 
      LOG.info("Number of files = " + numFiles);
 
      String path;
      StringparentPath = "";
      INodeDirectory parentINode = fsDir.rootDir;
      for (long i = 0; i < numFiles; i++) {
        long modificationTime = 0;
        long atime = 0;
        long blockSize = 0;
        //      ，         ，  “/a.txt”
        path = readString(in);
        replication = in.readShort();
        //        ，         minReplication maxReplication  ，     ，  
        //          
        replication = FSEditLog.adjustReplication(replication);
        modificationTime = in.readLong();
        if (imgVersion <= -17) {
          atime = in.readLong();
        }
        if (imgVersion <= -8) {
          blockSize = in.readLong();
        }
        //       
        int numBlocks = in.readInt();
        Block blocks[] = null;
 
        // for older versions, a blocklistof size 0
        // indicates a directory.
        if ((-9 <= imgVersion && numBlocks> 0) ||
            (imgVersion < -9 &&numBlocks >= 0)) {
          blocks = new Block[numBlocks];
          for (int j = 0; j < numBlocks; j++) {
            blocks[j] = new Block();
            if (-14 < imgVersion) {
              blocks[j].set(in.readLong(), in.readLong(),
                            Block.GRANDFATHER_GENERATION_STAMP);
            } else {
             //       ，   blockid，   ，    Stamp  ，  blockid      
             //           ，                ，           ，   
            //           ，    DATANODE  block       ，   block  ，  
            //     rebalance   ，               ，        blockid， 
            //      DATANODE   ，        ，      namenode   ，      
            //fsimage      。
              blocks[j].readFields(in);
            }
          }
        }
        // Older versions of HDFS does not storethe block size in inode.
        // If the file has more than one block, usethe size of the
        // first block as the blocksize.Otherwise use the default block size.
        //                ，    block       blocksize，       
        //         
        if (-8 <= imgVersion && blockSize ==0) {
          if (numBlocks > 1) {
            blockSize =blocks[0].getNumBytes();
          } else {
            long first = ((numBlocks == 1) ?blocks[0].getNumBytes(): 0);
            blockSize = Math.max(fsNamesys.getDefaultBlockSize(),first);
          }
        }
       
        //          ，        
        long nsQuota = -1L;
        if (imgVersion <= -16 && blocks == null) {
          nsQuota = in.readLong();
        }
        long dsQuota = -1L;
        if (imgVersion <= -18 && blocks == null) {
          dsQuota = in.readLong();
        }
       
        PermissionStatus permissions =fsNamesys.getUpgradePermission();
        if (imgVersion <= -11) {
          //         ，     、  、RWX  ，         user ownergroup  
        //      Linux        ，      
          permissions = PermissionStatus.read(in);
        }
 
        //      ，       ，          ，             ，      
        if (path.length() == 0) { // it is the root
          // update the root's attributes
          if (nsQuota != -1 || dsQuota != -1) {
            fsDir.rootDir.setQuota(nsQuota, dsQuota);
          }
          fsDir.rootDir.setModificationTime(modificationTime);
          fsDir.rootDir.setPermissionStatus(permissions);
          continue;
        }
        // check if the new inode belongs tothe same parent
        if(!isParent(path, parentPath)) {
          parentINode = null;
          parentPath = getParent(path);
        }
        //                  
        parentINode = fsDir.addToParent(path,parentINode, permissions,
                                        blocks,replication, modificationTime,
                                        atime,nsQuota, dsQuota, blockSize);
      }
     
      //   DATANODE  ，    1.0.4   ，         ，  fsimage       
      this.loadDatanodes(imgVersion, in);
 
      // load Files Under Construction
      this.loadFilesUnderConstruction(imgVersion, in,fsNamesys);
      //         ，      
      this.loadSecretManagerState(imgVersion, in,fsNamesys);
     
    } finally {
      in.close();
    }
   
    return needToSave;
  }