123 lines
3.4 KiB
Markdown
123 lines
3.4 KiB
Markdown
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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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