目前我们会把MapReduce Job运行完成后的Task运行的相关信息(status,cpu_time等)记录到后台DB中，监控系统会根据DB中记录的Task运行的相关信息，自动化预警。这些信息主要是从Job运行完成之后产生的相关historyFile中提取出来的。由于已经升级到Yarn，MRv2和MRv1在historyFile的处理上还是有些不同，在此做下简单的分析。
在MRv1中，与此相关最重要的类是org.apache.hadoop.mapred.JobHistory。在Job运行的时候，会首先将jobId_conf.xml和jobHistoryFile写入jt所在节点的本地存储，默认是hadoop.log.dir目录下(默认是/var/log/hadoop-0.20-mapreduce)，在作业运行完成后，将这两个文件移入DONE目录中(默认为hadoop.log.dir/history/done)，首先看下调用流程
重点说下moveToDone(JobID)方法，调用线程池中的线程异步的进行move操作，在移动之前，会在DONE目录下创建子目录，子目录创建的规则是
jt所在的host_启动时间(millisecond)_/YYYY/MM/DD/根据jobID截取的格式化字符串/
jobHistoryFile的命名规则是
jt-hostname_job-id_username_jobname
我们主要是从jobHistoryFile文件中提取信息，比如task类型，完成状态，运行所在节点，cpu时间，输入记录数，spill记录数等，jobHistoryFile中也包含所有计数器相关的信息。
升级到yarn后，MRv2的处理方式相比MRv1有所不同。在MRv2中,JobHistory作为独立的服务运行，对应的类是org.apache.hadoop.mapreduce.v2.hs.JobHistoryServer，日志写入HDFS中。JobHistoryServer在启动的时候会启动三种服务，最重要的jobHistoryService，负责加载和管理Job日志。clientService负责启动webapp服务和history server api服务。如果开启了日志聚集功能，aggLogDelService负责定期进行日志删除。
jobHistoryService的实现类是org.apache.hadoop.mapreduce.v2.hs.JobHistory，具体启动流程如下
JobHistory.start(){
scheduledExecutor = new ScheduledThreadPoolExecutor(2,
new ThreadFactoryBuilder().setNameFormat("Log Scanner/Cleaner #%d")
.build());
//在moveThreadInterval后周期执行MoveIntermediateToDoneRunnable
//也就是说,在job运行完成后,并不是马上将日志移动到done目录,而是可能会需要等
//一段时间(最长是moveThreadInterval)后再移动
scheduledExecutor.scheduleAtFixedRate(new MoveIntermediateToDoneRunnable(),
moveThreadInterval, moveThreadInterval, TimeUnit.MILLISECONDS);
// Start historyCleaner
boolean startCleanerService = conf.getBoolean(
JHAdminConfig.MR_HISTORY_CLEANER_ENABLE, true);
if (startCleanerService) {
long runInterval = conf.getLong(
JHAdminConfig.MR_HISTORY_CLEANER_INTERVAL_MS,
JHAdminConfig.DEFAULT_MR_HISTORY_CLEANER_INTERVAL_MS);
//周期执行historyCleaner
scheduledExecutor.scheduleAtFixedRate(new HistoryCleaner(),
30 * 1000l, runInterval, TimeUnit.MILLISECONDS);
}
}
Job运行过程中，相关日志文件写入hdfs://yarn.app.mapreduce.am.staging-dir/history/done_intermediate/$user目录下，user为运行Job的用户。在Job运行完成后，并不是像MRv1那样立即将相关文件移入DONE目录(DONE目录的路径为hdfs://yarn.app.mapreduce.am.staging-dir/history/done)，而是可能会需要等一段时间，线程会周期性的执行moveToDone。下面分析下MoveIntermediateToDoneRunnable线程主要的一个运行流程。
MoveIntermediateToDoneRunnable.run(){
hsManager.scanIntermediateDirectory();
}
HistoryFileManager.scanIntermediateDirectory{
//获取done_intermediate下的子目录
List userDirList = JobHistoryUtils.localGlobber(
intermediateDoneDirFc, intermediateDoneDirPath, "");
//遍历user子目录
for (FileStatus userDir : userDirList) {
String name = userDir.getPath().getName();
UserLogDir dir = userDirModificationTimeMap.get(name);
if(dir == null) {
dir = new UserLogDir();
UserLogDir old = userDirModificationTimeMap.putIfAbsent(name, dir);
if(old != null) {
dir = old;
}
}
//扫描user子目录
dir.scanIfNeeded(userDir);
}
}
HistoryFileManager$UserLogDir.scanIfNeeded(FileStatus fs) {
long newModTime = fs.getModificationTime();
//如果目录的修改时间和之前的不一致，则扫描此目录下的文件
if (modTime != newModTime) {
Path p = fs.getPath();
try {
scanIntermediateDirectory(p);
modTime = newModTime;
} catch (IOException e) {
LOG.error("Error while trying to scan the directory " + p, e);
}
}
}
HistoryFileManager.scanIntermediateDirectory(final Path absPath){
List fileStatusList = scanDirectoryForHistoryFiles(absPath,
intermediateDoneDirFc);
for (FileStatus fs : fileStatusList) {
//根据-拆解.jhist文件的文件名,设置属性jobIndexInfo的属性(user,jobName等)
JobIndexInfo jobIndexInfo = FileNameIndexUtils.getIndexInfo(fs.getPath()
.getName());
//JobID_conf.xml
String confFileName = JobHistoryUtils
.getIntermediateConfFileName(jobIndexInfo.getJobId());
//JobID.summary(MRv1中summary信息写入jt.log中)
String summaryFileName = JobHistoryUtils
.getIntermediateSummaryFileName(jobIndexInfo.getJobId());
//实例化HistoryFileInfo,state为IN_INTERMEDIATE
HistoryFileInfo fileInfo = new HistoryFileInfo(fs.getPath(), new Path(fs
.getPath().getParent(), confFileName), new Path(fs.getPath()
.getParent(), summaryFileName), jobIndexInfo, false);
final HistoryFileInfo old = jobListCache.addIfAbsent(fileInfo);
if (old == null || old.didMoveFail()) {
final HistoryFileInfo found = (old == null) ? fileInfo : old;
long cutoff = System.currentTimeMillis() - maxHistoryAge;
//超时需要删除的文件
if(found.getJobIndexInfo().getFinishTime() <= cutoff) {
try {
found.delete();
} catch (IOException e) {
LOG.warn("Error cleaning up a HistoryFile that is out of date.", e);
}
} else {
//异步调用moveToDone()
moveToDoneExecutor.execute(new Runnable() {
@Override
public void run() {
try {
found.moveToDone();
} catch (IOException e) {
LOG.info("Failed to process fileInfo for job: " +
found.getJobId(), e);
}
}
});
}
}
}
}
HistoryFileManager.moveToDone(){
if (!isMovePending()) {
return;
}
try {
long completeTime = jobIndexInfo.getFinishTime();
if (completeTime == 0) {
completeTime = System.currentTimeMillis();
}
JobId jobId = jobIndexInfo.getJobId();
List paths = new ArrayList(2);
if (historyFile == null) {
LOG.info("No file for job-history with " + jobId + " found in cache!");
} else {
paths.add(historyFile);
}
if (confFile == null) {
LOG.info("No file for jobConf with " + jobId + " found in cache!");
} else {
paths.add(confFile);
}
if (summaryFile == null) {
LOG.info("No summary file for job: " + jobId);
} else {
//删除掉summary file，不移动到done目录下
String jobSummaryString = getJobSummary(intermediateDoneDirFc,
summaryFile);
SUMMARY_LOG.info(jobSummaryString);
LOG.info("Deleting JobSummary file: [" + summaryFile + "]");
intermediateDoneDirFc.delete(summaryFile, false);
summaryFile = null;
}
//组装done目录下的目标目录(/user/history/done/YYYY/MM/DD/根据jobID截取的格式化 字符串)
Path targetDir = canonicalHistoryLogPath(jobId, completeTime);
addDirectoryToSerialNumberIndex(targetDir);
//创建目录
makeDoneSubdir(targetDir);
if (historyFile != null) {
Path toPath = doneDirFc.makeQualified(new Path(targetDir, historyFile
.getName()));
if (!toPath.equals(historyFile)) {
moveToDoneNow(historyFile, toPath);
historyFile = toPath;
}
}
if (confFile != null) {
Path toPath = doneDirFc.makeQualified(new Path(targetDir, confFile
.getName()));
if (!toPath.equals(confFile)) {
moveToDoneNow(confFile, toPath);
confFile = toPath;
}
}
state = HistoryInfoState.IN_DONE;
} catch (Throwable t) {
LOG.error("Error while trying to move a job to done", t);
this.state = HistoryInfoState.MOVE_FAILED;
}
}
.jhist文件中的内容被封装成了json格式，更便于解析，提供的内容也更全面。