Hadoop MapReduce Task Log 无法查看syslog问题

现象：

由于多个map task共用一个JVM，所以只输出了一组log文件

datanode01:/data/hadoop-x.x.x/logs/userlogs$ ls -R

.:

attempt_201211220735_0001_m_000000_0  attempt_201211220735_0001_m_000002_0  attempt_201211220735_0001_m_000005_0

attempt_201211220735_0001_m_000001_0  attempt_201211220735_0001_m_000003_0

./attempt_201211220735_0001_m_000000_0:

log.index

./attempt_201211220735_0001_m_000001_0:

log.index

./attempt_201211220735_0001_m_000002_0:

log.index  stderr  stdout  syslog

通过http://xxxxxxxx:50060/tasklog?attemptid= attempt_201211220735_0001_m_000000_0 获取task的日志时，会出现syslog无法获取

原因：

1.TaskLogServlet.doGet()方法

if (filter == null) {
        printTaskLog(response, out, attemptId,start, end, plainText,
                     TaskLog.LogName.STDOUT,isCleanup);
        printTaskLog(response, out, attemptId,start, end, plainText,
                     TaskLog.LogName.STDERR,isCleanup);
        if(haveTaskLog(attemptId, isCleanup, TaskLog.LogName.SYSLOG)) {
          printTaskLog(response, out,attemptId, start, end, plainText,
              TaskLog.LogName.SYSLOG,isCleanup);
        }
        if(haveTaskLog(attemptId, isCleanup, TaskLog.LogName.DEBUGOUT)) {
          printTaskLog(response, out,attemptId, start, end, plainText,
                       TaskLog.LogName.DEBUGOUT, isCleanup);
        }
        if(haveTaskLog(attemptId, isCleanup, TaskLog.LogName.PROFILE)) {
          printTaskLog(response, out,attemptId, start, end, plainText,
                       TaskLog.LogName.PROFILE,isCleanup);
        }
      } else {
        printTaskLog(response, out, attemptId,start, end, plainText, filter,
                     isCleanup);
     }

尝试将filter=SYSLOG参数加上，可以访问到syslog,但去掉就不行。

看了代码多了一行

haveTaskLog(attemptId, isCleanup,TaskLog.LogName.SYSLOG)

判断，跟进代码发现，检查的是原来

attempt_201211220735_0001_m_000000_0目录下是否有syslog文件？

而不是从log.index找location看是否有syslog文件，一个bug出现了！

2.TaskLogServlet. printTaskLog方法

获取日志文件时会从log.index读取。

InputStreamtaskLogReader =
       new TaskLog.Reader(taskId,filter, start, end, isCleanup);
TaskLog.Reader
public Reader(TaskAttemptIDtaskid, LogName kind,
                  long start,long end, boolean isCleanup) throwsIOException {
      // find the right log file
      Map<LogName, LogFileDetail>allFilesDetails =
         getAllLogsFileDetails(taskid, isCleanup);

static Map<LogName, LogFileDetail> getAllLogsFileDetails(
      TaskAttemptID taskid, booleanisCleanup) throws IOException {

    Map<LogName, LogFileDetail>allLogsFileDetails =
        newHashMap<LogName, LogFileDetail>();

    File indexFile = getIndexFile(taskid,isCleanup);
    BufferedReader fis;
    try {
      fis = newBufferedReader(new InputStreamReader(
        SecureIOUtils.openForRead(indexFile,obtainLogDirOwner(taskid))));
    } catch(FileNotFoundException ex) {
      LOG.warn("Index file for the log of " + taskid + " does not exist.");

      //Assume no task reuse is used and files exist on attemptdir
      StringBuffer input = newStringBuffer();
      input.append(LogFileDetail.LOCATION
                     + getAttemptDir(taskid,isCleanup) + "\n");
      for(LogName logName : LOGS_TRACKED_BY_INDEX_FILES) {
        input.append(logName + ":0 -1\n");
      }
      fis = newBufferedReader(new StringReader(input.toString()));
}
………………….

问题解决：

类似getAllLogsFileDetails一样，先从log.index获取日志目录获取logdir，

 File indexFile = getIndexFile(taskid,isCleanup);
    BufferedReader fis;
    try {
      fis = newBufferedReader(new InputStreamReader(
        SecureIOUtils.openForRead(indexFile,obtainLogDirOwner(taskid))));
    } catch(FileNotFoundException ex) {
      LOG.warn("Index file for the log of " + taskid + " does not exist.");

      //Assume no task reuse is used and files exist on attemptdir
      StringBuffer input = newStringBuffer();
      input.append(LogFileDetail.LOCATION
                     + getAttemptDir(taskid,isCleanup) + "\n");
      for(LogName logName : LOGS_TRACKED_BY_INDEX_FILES) {
        input.append(logName + ":0 -1\n");
      }
      fis = newBufferedReader(new StringReader(input.toString()));
    }
    String str = fis.readLine();
    if (str== null) { //thefile doesn't have anything
      throw newIOException ("Index file for the log of " + taskid+"is empty.");
    }
    String loc =str.substring(str.indexOf(LogFileDetail.LOCATION)+
       LogFileDetail.LOCATION.length());

从logdir中判断是否有syslog。

Workaround:

查询时加入在url上加入filter=SYSLOG就可以看到,不需要修改代码。