【框架解析】Hadoop系统分析(五)--namenode其他

upgrade/rollback/importCheckpoint

在FsImage.recoverTransitionRead方法中，针对upgrade/rollback/importCheckpoint参数，在启动前做了特殊的操作，代码如下：

switch(startOpt) {    case UPGRADE:      doUpgrade();      return false; // upgrade saved image already    case IMPORT:      doImportCheckpoint();      return true;    case ROLLBACK:      doRollback();      break;    case REGULAR:      // just load the image    }

1. hadoop namenode -upgrade
   进行hadoop namenode的升级操作。调用FsImage.doUpgrade方法，主要操作是将current保存为previous，升级后的fsimage保存为current。
   

   if(getDistributedUpgradeState()) {      // only distributed upgrade need to continue      // don't do version upgrade      this.loadFSImage();      initializeDistributedUpgrade();      return;    }    // Upgrade is allowed only if there are     // no previous fs states in any of the directories    for (Iterator<StorageDirectory> it =                            dirIterator(); it.hasNext();) {      StorageDirectory sd = it.next();      //如果已经有previous目录，则无法重新upgrade      if (sd.getPreviousDir().exists())        throw new InconsistentFSStateException(sd.getRoot(),                                               "previous fs state should not exist during upgrade. "                                               + "Finalize or rollback first.");    }    // 把硬盘上最近的fsimage加载进内存    this.loadFSImage();    // Do upgrade for each directory    long oldCTime = this.getCTime();    this.cTime = FSNamesystem.now();  // generate new cTime for the state    int oldLV = this.getLayoutVersion();    this.layoutVersion = FSConstants.LAYOUT_VERSION;    this.checkpointTime = FSNamesystem.now();    for (Iterator<StorageDirectory> it =                            dirIterator(); it.hasNext();) {      StorageDirectory sd = it.next();      LOG.info("Upgrading image directory " + sd.getRoot()               + ".\n   old LV = " + oldLV               + "; old CTime = " + oldCTime               + ".\n   new LV = " + this.getLayoutVersion()               + "; new CTime = " + this.getCTime());      File curDir = sd.getCurrentDir();      File prevDir = sd.getPreviousDir();      File tmpDir = sd.getPreviousTmp();      assert curDir.exists() : "Current directory must exist.";      assert !prevDir.exists() : "prvious directory must not exist.";      assert !tmpDir.exists() : "prvious.tmp directory must not exist.";      // 把current目录改为previous.tmp目录      rename(curDir, tmpDir);      // 把内存中的fsimage保存到current中      saveCurrent(sd);      // 把previous.tmp目录修改为previous目录      rename(tmpDir, prevDir);      //标记升级没有完成(升级成功需要进行finalize，升级失败需要进行rollback来完成升级)      isUpgradeFinalized = false;      LOG.info("Upgrade of " + sd.getRoot() + " is complete.");    }    //初始化升级后操作，主要是计算version写VERSION文件    initializeDistributedUpgrade();    //开启editlog    editLog.open();

2. hadoop namenode -rollback
   升级hadoop失败后回滚，主要是把upgrade时变更的数据目录恢复原状，将current修改为removed.tmp，previous修改回current，最后删除removed.tmp
   

   // Rollback is allowed only if there is     // a previous fs states in at least one of the storage directories.    // Directories that don't have previous state do not rollback    boolean canRollback = false;    FSImage prevState = new FSImage();    prevState.layoutVersion = FSConstants.LAYOUT_VERSION;    for (Iterator<StorageDirectory> it =                        dirIterator(); it.hasNext();) {      //将previous目录里的版本信息加载进内存，如果没有previous目录，则加载current目录      StorageDirectory sd = it.next();      File prevDir = sd.getPreviousDir();      if (!prevDir.exists()) {  // use current directory then        LOG.info("Storage directory " + sd.getRoot()                 + " does not contain previous fs state.");        sd.read(); // read and verify consistency with other directories        continue;      }      StorageDirectory sdPrev = prevState.new StorageDirectory(sd.getRoot());      sdPrev.read(sdPrev.getPreviousVersionFile());  // read and verify consistency of the prev dir      canRollback = true;    }    if (!canRollback)      throw new IOException("Cannot rollback. "                             + "None of the storage directories contain previous fs state.");    // Now that we know all directories are going to be consistent    // Do rollback for each directory containing previous state    for (Iterator<StorageDirectory> it =                           dirIterator(); it.hasNext();) {      StorageDirectory sd = it.next();      File prevDir = sd.getPreviousDir();      if (!prevDir.exists())        continue;      LOG.info("Rolling back storage directory " + sd.getRoot()               + ".\n   new LV = " + prevState.getLayoutVersion()               + "; new CTime = " + prevState.getCTime());      File tmpDir = sd.getRemovedTmp();      assert !tmpDir.exists() : "removed.tmp directory must not exist.";      // rename current to tmp      File curDir = sd.getCurrentDir();      assert curDir.exists() : "Current directory must exist.";      //将current目录更改为removed.tmp      rename(curDir, tmpDir);      // rename previous to current      //将previous更改为current      rename(prevDir, curDir);      // delete tmp dir      //删除removed.tmp      deleteDir(tmpDir);      LOG.info("Rollback of " + sd.getRoot()+ " is complete.");    }    isUpgradeFinalized = true;    // check whether name-node can start in regular mode    verifyDistributedUpgradeProgress(StartupOption.REGULAR);

3. hadoop namenode -importCheckpoint
   使用备份的checkpoint启动namenode，之后将加载进来的ckp保存为current
   

   FSImage ckptImage = new FSImage();    FSNamesystem fsNamesys = FSNamesystem.getFSNamesystem();    // replace real image with the checkpoint image    FSImage realImage = fsNamesys.getFSImage();    assert realImage == this;    fsNamesys.dir.fsImage = ckptImage;    // load from the checkpoint dirs    try {      //读取checkpointDirs目录与checkpointEditsDirs目录，合并后放入内存      //checkpointDirs值为fs.checkpoint.dir配置项，如果没有则为null,secondarynamenode上默认值为/tmp/hadoop/dfs/namesecondary      //checkpointEditsDirs值为fs.checkpoint.edits.dir配置项，如果没有则为null，secondarynamenode上默认值为/tmp/hadoop/dfs/namesecondary      ckptImage.recoverTransitionRead(checkpointDirs, checkpointEditsDirs,                                              StartupOption.REGULAR);    } finally {      ckptImage.close();    }    // return back the real image    realImage.setStorageInfo(ckptImage);    fsNamesys.dir.fsImage = realImage;    // and save it 保存fsimage    saveNamespace(false);

hadoop namenode -finalize
升级完成后，使用hadoop namenode -finalize来进行确认，finalize之后就不能rollback了
回到NameNode.createNameNode方法中，进入FINALIZE分支

case FINALIZE:        aborted = finalize(conf, true);        System.exit(aborted ? 1 : 0);

之后进入FSImage.doFinalize进行完成升级，主要工作就是删除previous目录，标记升级结束

File prevDir = sd.getPreviousDir();    if (!prevDir.exists()) { // already discarded      LOG.info("Directory " + prevDir + " does not exist.");      LOG.info("Finalize upgrade for " + sd.getRoot()+ " is not required.");      return;    }    LOG.info("Finalizing upgrade for storage directory "              + sd.getRoot() + "."             + (getLayoutVersion()==0 ? "" :                   "\n   cur LV = " + this.getLayoutVersion()                   + "; cur CTime = " + this.getCTime()));    assert sd.getCurrentDir().exists() : "Current directory must exist.";    final File tmpDir = sd.getFinalizedTmp();    // rename previous to tmp and remove    //将previous修改为finalized.tmp    rename(prevDir, tmpDir);    //删除finalized.tmp    deleteDir(tmpDir);    isUpgradeFinalized = true;    LOG.info("Finalize upgrade for " + sd.getRoot()+ " is complete.");