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# 简介
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本章详细介绍NameNode启动过程。主要是代码级别的解释。
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nameNode的启动主要是有NameNode.java主导的，由main函数开始了解。
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下面是main函数里面的主要内容，可以看到主要由createNameNode实现NameNode的启动。
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```java
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NameNode namenode = createNameNode(argv, null);
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if (namenode != null) {
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namenode.join();
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}
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```
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在createNameNode函数里面主要是分为两部分：
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- 参数解析：主要关心解析startOpt，startOpt可以控制具体操作，比如format、rockback等。主要操作如下,后续会详细介绍。
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```java
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FORMAT ("-format"),
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CLUSTERID ("-clusterid"),
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GENCLUSTERID ("-genclusterid"),
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REGULAR ("-regular"),
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BACKUP ("-backup"),
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CHECKPOINT("-checkpoint"),
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UPGRADE ("-upgrade"),
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ROLLBACK("-rollback"),
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ROLLINGUPGRADE("-rollingUpgrade"),
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IMPORT ("-importCheckpoint"),
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BOOTSTRAPSTANDBY("-bootstrapStandby"),
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INITIALIZESHAREDEDITS("-initializeSharedEdits"),
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RECOVER ("-recover"),
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FORCE("-force"),
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NONINTERACTIVE("-nonInteractive"),
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SKIPSHAREDEDITSCHECK("-skipSharedEditsCheck"),
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RENAMERESERVED("-renameReserved"),
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METADATAVERSION("-metadataVersion"),
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UPGRADEONLY("-upgradeOnly"),
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HOTSWAP("-hotswap"),
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OBSERVER("-observer");
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```
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模型情况下会走到启动的启动的流程里面。
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- 启动NameNode或者其他操作，比如format等。
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## 启动
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NameNode的核心主要在NameNode的构造函数里面。
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```java
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this.haEnabled = HAUtil.isHAEnabled(conf, nsId);
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// 检查HA的状态，主要是判断当前启动的是主实例还是备实例
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state = createHAState(getStartupOption(conf));
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this.allowStaleStandbyReads = HAUtil.shouldAllowStandbyReads(conf);
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this.haContext = createHAContext();
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try {
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initializeGenericKeys(conf, nsId, namenodeId);
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// 启动NameNode
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initialize(getConf());
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state.prepareToEnterState(haContext);
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try {
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haContext.writeLock();
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state.enterState(haContext);
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} finally {
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haContext.writeUnlock();
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}
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} catch (IOException e) {
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this.stopAtException(e);
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throw e;
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} catch (HadoopIllegalArgumentException e) {
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this.stopAtException(e);
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throw e;
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}
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```
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initialize函数详解如下：
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```java
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protected void initialize(Configuration conf) throws IOException {
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// .... 省略
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//登录kerberos
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UserGroupInformation.setConfiguration(conf);
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loginAsNameNodeUser(conf);
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// 初始化监控信息
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NameNode.initMetrics(conf, this.getRole());
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StartupProgressMetrics.register(startupProgress);
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pauseMonitor = new JvmPauseMonitor();
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pauseMonitor.init(conf);
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pauseMonitor.start();
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metrics.getJvmMetrics().setPauseMonitor(pauseMonitor);
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// .... 省略
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if (NamenodeRole.NAMENODE == role) {
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startHttpServer(conf);
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}
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// 从本地加载FSImage，并且与Editlog合并产生新的FSImage
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loadNamesystem(conf);
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//TODO 待确认用途
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startAliasMapServerIfNecessary(conf);
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//创建rpcserver，封装了NameNodeRpcServer、ClientRPCServer
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//支持ClientNameNodeProtocol、DataNodeProtocolPB等协议
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rpcServer = createRpcServer(conf);
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initReconfigurableBackoffKey();
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// .... 省略
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if (NamenodeRole.NAMENODE == role) {
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httpServer.setNameNodeAddress(getNameNodeAddress());
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httpServer.setFSImage(getFSImage());
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if (levelDBAliasMapServer != null) {
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httpServer.setAliasMap(levelDBAliasMapServer.getAliasMap());
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}
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}
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//启动执行多个重要的工作线程
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startCommonServices(conf);
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startMetricsLogger(conf);
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}
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```
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### startCommonServices函数详解
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启动NameNode关键服务
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```java
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private void startCommonServices(Configuration conf) throws IOException {
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// 创建NameNodeResourceChecker、激活BlockManager等
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namesystem.startCommonServices(conf, haContext);
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registerNNSMXBean();
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if (NamenodeRole.NAMENODE != role) {
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startHttpServer(conf);
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httpServer.setNameNodeAddress(getNameNodeAddress());
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httpServer.setFSImage(getFSImage());
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if (levelDBAliasMapServer != null) {
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httpServer.setAliasMap(levelDBAliasMapServer.getAliasMap());
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}
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}
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// 启动rpc服务
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rpcServer.start();
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try {
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// 获取启动插件列表
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plugins = conf.getInstances(DFS_NAMENODE_PLUGINS_KEY,
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ServicePlugin.class);
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} catch (RuntimeException e) {
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String pluginsValue = conf.get(DFS_NAMENODE_PLUGINS_KEY);
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LOG.error("Unable to load NameNode plugins. Specified list of plugins: " +
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pluginsValue, e);
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throw e;
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}
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// 启动所有插件
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for (ServicePlugin p: plugins) {
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try {
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// 调用插件的start接口，需要插件自己实现，需要实现接口ServicePlugin
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p.start(this);
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} catch (Throwable t) {
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LOG.warn("ServicePlugin " + p + " could not be started", t);
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}
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}
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LOG.info(getRole() + " RPC up at: " + getNameNodeAddress());
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if (rpcServer.getServiceRpcAddress() != null) {
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LOG.info(getRole() + " service RPC up at: "
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+ rpcServer.getServiceRpcAddress());
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}
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}
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```
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### namesystem.startCommonServices
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在当前函数中启动blockManager和NameNodeResourceChecker，blockManager比较关键。
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```java
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void startCommonServices(Configuration conf, HAContext haContext) throws IOException {
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this.registerMBean(); // register the MBean for the FSNamesystemState
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writeLock();
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this.haContext = haContext;
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try {
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//创建NameNodeResourceChecker，并立即检查一次
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nnResourceChecker = new NameNodeResourceChecker(conf);
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checkAvailableResources();
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assert !blockManager.isPopulatingReplQueues();
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StartupProgress prog = NameNode.getStartupProgress();
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prog.beginPhase(Phase.SAFEMODE);
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//获取已完成的数据块总量
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long completeBlocksTotal = getCompleteBlocksTotal();
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prog.setTotal(Phase.SAFEMODE, STEP_AWAITING_REPORTED_BLOCKS,
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completeBlocksTotal);
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// 激活blockManager，blockManager负责管理文件系统中文件的物理块与实际存储位置的映射关系，
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// 是NameNode的核心功能之一。
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blockManager.activate(conf, completeBlocksTotal);
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} finally {
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writeUnlock("startCommonServices");
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}
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registerMXBean();
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DefaultMetricsSystem.instance().register(this);
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if (inodeAttributeProvider != null) {
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inodeAttributeProvider.start();
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dir.setINodeAttributeProvider(inodeAttributeProvider);
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}
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// 注册快照管理器
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snapshotManager.registerMXBean();
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InetSocketAddress serviceAddress = NameNode.getServiceAddress(conf, true);
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this.nameNodeHostName = (serviceAddress != null) ? serviceAddress.getHostName() : "";
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}
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```
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### blockManager.activate
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启动blockManager.activate 主要是初始化blockManager。
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主要包含下面几个方面:
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- pendingReconstruction
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- datanodeManager
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- bmSafeMode
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```java
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public void activate(Configuration conf, long blockTotal) {
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pendingReconstruction.start();
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// 初始化datanodeManager
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datanodeManager.activate(conf);
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this.redundancyThread.setName("RedundancyMonitor");
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this.redundancyThread.start();
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this.markedDeleteBlockScrubberThread.setName("MarkedDeleteBlockScrubberThread");
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this.markedDeleteBlockScrubberThread.start();
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this.blockReportThread.start();
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mxBeanName = MBeans.register("NameNode", "BlockStats", this);
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bmSafeMode.activate(blockTotal);
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}
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```
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