374 lines
13 KiB
Markdown
374 lines
13 KiB
Markdown
# 作业启动
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作业提交的客户端比较核心的类是Job.java，看作业启动的源码需要从这个类开始看。
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## Job.java
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作业启动的入口函数为waitForCompletion函数。当前函数的核心函数为submit()，主要如下：
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```java
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public void submit()
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throws IOException, InterruptedException, ClassNotFoundException {
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ensureState(JobState.DEFINE);
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setUseNewAPI();
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connect();
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final JobSubmitter submitter =
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getJobSubmitter(cluster.getFileSystem(), cluster.getClient());
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status = ugi.doAs(new PrivilegedExceptionAction<JobStatus>() {
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public JobStatus run() throws IOException, InterruptedException,
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ClassNotFoundException {
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return submitter.submitJobInternal(Job.this, cluster);
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}
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});
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state = JobState.RUNNING;
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LOG.info("The url to track the job: " + getTrackingURL());
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}
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```
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其中，connect主要为连接ResourceManager。核心提交类为submitJobInternal，在submitJobInternal中主要包含：
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- 检查是否开启分布式缓存，核心函数为：`addMRFrameworkToDistributedCache(conf);`
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- 从yarn上面获取Yarn ApplicationId。
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- 将需要上传的文件拷贝到submitJobDir下面，将上传的结果添加到指定的配置中。主要实现在函数`copyAndConfigureFiles(job, submitJobDir);`里面，主要上传当前作业需要的jar包等信息到staging目录。当上传Jar包比较频繁的时候可以考虑开启分布式缓存。
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- 初始化核心配置，主要实现在函数：`writeConf(conf, submitJobFile);`里面。
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- 最后才是真正提交作业的部分：`status = submitClient.submitJob(jobId, submitJobDir.toString(), job.getCredentials());`通过submitClient.submitJob之后是远程调用到ResourceManager的类：YARNRunner.java，开始作业提交。
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## YARNRunner.java
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在当前类中，处理逻辑主要包含下面几步：
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- 创建上下问信息：ApplicationSubmissionContext，当前这一步当中主要是构造AM相关参数，比如AM的启动命令等。在AM的启动命令中会设置AM的启动主函数MRAppMaster，在资源调度到当前作业时，会先启动AM的主函数MRAppMaster
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- 提交作业。最后会调用到`rmClient.submitApplication(request);`发送启动作业的请求，在发送请求之后会一直等到作业启动完成。启动成功之后会返回appilicationId
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## 资源调度
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Yarn资源调度过程待完善，后面会单独章节学习。
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## MRAppMaster.java
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当前类是启动AM的入口函数，所以要从main函数开始读代码。main函数里面主要做了下面几件事：
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- 初始化MRAppMaster实例。
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- 加载job.xml信息。
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- 初始化web信息。主要包含： MR history server、MR Server。
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- 启动APPMaster。
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### initAndStartAppMaster：启动AppMaster
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MRAppMaster在yarn内部是一个服务，最终启动的时候会调用到serviceStart函数里面，所以我们主要看这个函数里面做了什么。
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#### 1、创建并且初始化Job
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创建Job对象并且将其初始化掉。但是不会启动当前作业。
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- 初始化JobImpl对象。在JobImpl初始化的时候做了下面几件事：
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- 初始化线程池。
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- 初始化作业状态机的核心代码如下：
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```java
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protected static final
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StateMachineFactory<JobImpl, JobStateInternal, JobEventType, JobEvent>
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stateMachineFactory
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= new StateMachineFactory<JobImpl, JobStateInternal, JobEventType, JobEvent>
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(JobStateInternal.NEW)
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// Transitions from NEW state
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.addTransition(JobStateInternal.NEW, JobStateInternal.NEW,
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JobEventType.JOB_DIAGNOSTIC_UPDATE,
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DIAGNOSTIC_UPDATE_TRANSITION)
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.addTransition(JobStateInternal.NEW, JobStateInternal.NEW,
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JobEventType.JOB_COUNTER_UPDATE, COUNTER_UPDATE_TRANSITION)
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// ....省略...
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.addTransition(JobStateInternal.REBOOT, JobStateInternal.REBOOT,
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JobEventType.JOB_COUNTER_UPDATE, COUNTER_UPDATE_TRANSITION)
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// create the topology tables
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.installTopology();
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- 初始化其他配置。
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- 在中央处理器里面注册JobFinishEvent类型事件以及事件处理的handler。
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```java
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protected Job createJob(Configuration conf, JobStateInternal forcedState,
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String diagnostic) {
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// create single job
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Job newJob =
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new JobImpl(jobId, appAttemptID, conf, dispatcher.getEventHandler(),
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taskAttemptListener, jobTokenSecretManager, jobCredentials, clock,
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completedTasksFromPreviousRun, metrics,
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committer, newApiCommitter,
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currentUser.getUserName(), appSubmitTime, amInfos, context,
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forcedState, diagnostic);
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((RunningAppContext) context).jobs.put(newJob.getID(), newJob);
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dispatcher.register(JobFinishEvent.Type.class,
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createJobFinishEventHandler());
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return newJob;
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}
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```
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#### 2、发送inited事件
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发送inited事件的对象主要是下面两个：
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- 通过dispatcher给历史AM发送。
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- 当前AM。代码如下：
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```java
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// Send out an MR AM inited event for this AM.
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dispatcher.getEventHandler().handle(
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new JobHistoryEvent(job.getID(), new AMStartedEvent(amInfo
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.getAppAttemptId(), amInfo.getStartTime(), amInfo.getContainerId(),
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amInfo.getNodeManagerHost(), amInfo.getNodeManagerPort(), amInfo
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.getNodeManagerHttpPort(), this.forcedState == null ? null
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: this.forcedState.toString(), appSubmitTime)));
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```
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#### 3、创建job init事件，并且处理
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创建init事件，核心代码如下：
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```java
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JobEvent initJobEvent = new JobEvent(job.getID(), JobEventType.JOB_INIT);
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jobEventDispatcher.handle(initJobEvent);
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```
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事件处理的核心类为InitTransition，核心代码如下：
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```java
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public JobStateInternal transition(JobImpl job, JobEvent event) {
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job.metrics.submittedJob(job);
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job.metrics.preparingJob(job);
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// 初始化上下文。
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if (job.newApiCommitter) {
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job.jobContext = new JobContextImpl(job.conf,
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job.oldJobId);
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} else {
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job.jobContext = new org.apache.hadoop.mapred.JobContextImpl(
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job.conf, job.oldJobId);
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}
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try {
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// 初始化token等信息。
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setup(job);
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job.fs = job.getFileSystem(job.conf);
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//log to job history
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JobSubmittedEvent jse = new JobSubmittedEvent(job.oldJobId,
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job.conf.get(MRJobConfig.JOB_NAME, "test"),
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job.conf.get(MRJobConfig.USER_NAME, "mapred"),
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job.appSubmitTime,
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job.remoteJobConfFile.toString(),
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job.jobACLs, job.queueName,
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job.conf.get(MRJobConfig.WORKFLOW_ID, ""),
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job.conf.get(MRJobConfig.WORKFLOW_NAME, ""),
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job.conf.get(MRJobConfig.WORKFLOW_NODE_NAME, ""),
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getWorkflowAdjacencies(job.conf),
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job.conf.get(MRJobConfig.WORKFLOW_TAGS, ""), job.conf);
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job.eventHandler.handle(new JobHistoryEvent(job.jobId, jse));
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//TODO JH Verify jobACLs, UserName via UGI?
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// 初始化并行度等信息。
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TaskSplitMetaInfo[] taskSplitMetaInfo = createSplits(job, job.jobId);
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job.numMapTasks = taskSplitMetaInfo.length;
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job.numReduceTasks = job.conf.getInt(MRJobConfig.NUM_REDUCES, 0);
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if (job.numMapTasks == 0 && job.numReduceTasks == 0) {
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job.addDiagnostic("No of maps and reduces are 0 " + job.jobId);
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} else if (job.numMapTasks == 0) {
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job.reduceWeight = 0.9f;
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} else if (job.numReduceTasks == 0) {
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job.mapWeight = 0.9f;
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} else {
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job.mapWeight = job.reduceWeight = 0.45f;
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}
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checkTaskLimits();
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// 加载其他参数，具体代码省略。。
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cleanupSharedCacheUploadPolicies(job.conf);
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// create the Tasks but don't start them yet，， 创建map task
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createMapTasks(job, inputLength, taskSplitMetaInfo);
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// 创建reduce tasks
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createReduceTasks(job);
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job.metrics.endPreparingJob(job);
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return JobStateInternal.INITED;
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} catch (Exception e) {
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LOG.warn("Job init failed", e);
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job.metrics.endPreparingJob(job);
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job.addDiagnostic("Job init failed : "
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+ StringUtils.stringifyException(e));
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// Leave job in the NEW state. The MR AM will detect that the state is
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// not INITED and send a JOB_INIT_FAILED event.
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return JobStateInternal.NEW;
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}
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}
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```
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#### 4、检查初始化结果并且启动作业
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当init成功时，handler返回的结果是JobStateInternal.INITED；如果是失败了则返回的结果是JobStateInternal.NEW。
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对于初始化失败的作业会触发JobEventType.JOB_INIT_FAILED事件。
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对于初始化成功的作业会调用函数startJobs，继续启动作业。触发
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```java
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protected void startJobs() {
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/** create a job-start event to get this ball rolling */
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JobEvent startJobEvent = new JobStartEvent(job.getID(),
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recoveredJobStartTime);
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/** send the job-start event. this triggers the job execution. */
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dispatcher.getEventHandler().handle(startJobEvent);
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}
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```
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核心处理逻辑如下，主要是触发了几个事件：
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- JobHistoryEvent：事件处理的handler为JobHistoryEventHandler。
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- JobInfoChangeEvent：
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- CommitterJobSetupEvent：作业启动的事件，核心处理逻辑在EventProcessor中的函数handleJobSetup中。
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```java
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public void transition(JobImpl job, JobEvent event) {
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JobStartEvent jse = (JobStartEvent) event;
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if (jse.getRecoveredJobStartTime() != -1L) {
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job.startTime = jse.getRecoveredJobStartTime();
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} else {
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job.startTime = job.clock.getTime();
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}
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JobInitedEvent jie =
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new JobInitedEvent(job.oldJobId,
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job.startTime,
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job.numMapTasks, job.numReduceTasks,
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job.getState().toString(),
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job.isUber());
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job.eventHandler.handle(new JobHistoryEvent(job.jobId, jie));
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JobInfoChangeEvent jice = new JobInfoChangeEvent(job.oldJobId,
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job.appSubmitTime, job.startTime);
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job.eventHandler.handle(new JobHistoryEvent(job.jobId, jice));
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job.metrics.runningJob(job);
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job.eventHandler.handle(new CommitterJobSetupEvent(
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job.jobId, job.jobContext));
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}
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```
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handleJobSetup的核心处理逻辑：
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- 创建attempt路径。
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- 触发JobSetupCompletedEvent事件。从事件实现来看会触发JobImpl里面的JOB_SETUP_COMPLETED事件类型，由SetupCompletedTransition来处理当前事件。在当前函数里面会触发JOB_COMPLETED事件。最终会走到JobImpl的checkReadyForCommit函数里面。
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```java
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protected void handleJobSetup(CommitterJobSetupEvent event) {
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try {
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// 主要是创建attempt路径
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committer.setupJob(event.getJobContext());
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context.getEventHandler().handle(
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new JobSetupCompletedEvent(event.getJobID()));
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} catch (Exception e) {
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LOG.warn("Job setup failed", e);
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context.getEventHandler().handle(new JobSetupFailedEvent(
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event.getJobID(), StringUtils.stringifyException(e)));
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}
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}
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```
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SetupCompletedTransition的处理逻辑如下，可以看到会定时启动MapTask和ReduceTask。
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```java
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public void transition(JobImpl job, JobEvent event) {
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job.setupProgress = 1.0f;
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job.scheduleTasks(job.mapTasks, job.numReduceTasks == 0);
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job.scheduleTasks(job.reduceTasks, true);
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// If we have no tasks, just transition to job completed
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if (job.numReduceTasks == 0 && job.numMapTasks == 0) {
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job.eventHandler.handle(new JobEvent(job.jobId,
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JobEventType.JOB_COMPLETED));
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}
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}
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```
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checkReadyForCommit函数的实现如下，可以看到在触发了CommitterJobCommitEvent事件,在CommitterJobCommitEvent里面会触发JOB_COMMIT事件。主要处理逻辑在handleJobCommit里面。
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```java
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protected JobStateInternal checkReadyForCommit() {
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JobStateInternal currentState = getInternalState();
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if (completedTaskCount == tasks.size()
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&& currentState == JobStateInternal.RUNNING) {
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eventHandler.handle(new CommitterJobCommitEvent(jobId, getJobContext()));
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return JobStateInternal.COMMITTING;
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}
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// return the current state as job not ready to commit yet
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return getInternalState();
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}
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```
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handleJobCommit处理逻辑如下，
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```java
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protected void handleJobCommit(CommitterJobCommitEvent event) {
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boolean commitJobIsRepeatable = false;
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try {
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// 检查作业是否重复。
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commitJobIsRepeatable = committer.isCommitJobRepeatable(
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event.getJobContext());
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} catch (IOException e) {
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LOG.warn("Exception in committer.isCommitJobRepeatable():", e);
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}
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try {
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// 创建文件：/tmp/hadoop-yarn/staging//user/.staging/{jobid}/COMMIT_STARTED
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touchz(startCommitFile, commitJobIsRepeatable);
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jobCommitStarted();
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// 检查和RM的心跳。
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waitForValidCommitWindow();
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// 提交作业，核心处理函数在commitJobInternal里面
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committer.commitJob(event.getJobContext());
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// 创建文件：/tmp/hadoop-yarn/staging//user/.staging/{jobid}/COMMIT_SUCCESS
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touchz(endCommitSuccessFile, commitJobIsRepeatable);
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context.getEventHandler().handle(
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new JobCommitCompletedEvent(event.getJobID()));
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} catch (Exception e) {
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LOG.error("Could not commit job", e);
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try {
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// 失败之后创建：/tmp/hadoop-yarn/staging//user/.staging/{jobid}/COMMIT_FAIL
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touchz(endCommitFailureFile, commitJobIsRepeatable);
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} catch (Exception e2) {
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LOG.error("could not create failure file.", e2);
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}
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context.getEventHandler().handle(
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new JobCommitFailedEvent(event.getJobID(),
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StringUtils.stringifyException(e)));
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} finally {
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jobCommitEnded();
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}
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}
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```
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##### CommitSucceededTransition
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提交成功的事件处理handler为CommitSucceededTransition，核心处理逻辑如下：
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```java
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job.logJobHistoryFinishedEvent();
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job.finished(JobStateInternal.SUCCEEDED);
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```
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