Hadoop MapReduce Task Log 無法查看syslog問題

現象：

由於多個map task共用一個JVM，所以只輸出了一組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

 

通過http://xxxxxxxx:50060/tasklog?attemptid= attempt_201211220735_0001_m_000000_0 獲取task的日誌時，會出現syslog無法獲取

 

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);
     }

 

嘗試將filter=SYSLOG參數加上，可以訪問到syslog,但去掉就不行。

看了代碼多了一行

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

判斷，跟進代碼發現，檢查的是原來

attempt_201211220735_0001_m_000000_0目錄下是否有syslog文件？

而不是從log.index找location看是否有syslog文件，一個bug出現了！

 

2.TaskLogServlet. printTaskLog方法

獲取日誌文件時會從log.index讀取。

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()));
}
………………….

 

問題解決：

類似getAllLogsFileDetails一樣，先從log.index獲取日誌目錄獲取logdir，

  

private boolean haveTaskLog(TaskAttemptID taskId, boolean isCleanup,
        TaskLog.LogName type) throws IOException {
    File f = TaskLog.getTaskLogFile(taskId, isCleanup, type);
    if (f.exists() && f.canRead()) {
        return true;
    } else {
        File indexFile = TaskLog.getIndexFile(taskId, isCleanup);
        if (!indexFile.exists()) {
            return false;
        }
 
 
        BufferedReader fis;
        try {
            fis = new BufferedReader(new InputStreamReader(
                    SecureIOUtils.openForRead(indexFile,
                            TaskLog.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 = new StringBuffer();
            input.append(LogFileDetail.LOCATION
                    + TaskLog.getAttemptDir(taskId, isCleanup) + "\n");
            for (LogName logName : TaskLog.LOGS_TRACKED_BY_INDEX_FILES) {
                input.append(logName + ":0 -1\n");
            }
            fis = new BufferedReader(new StringReader(input.toString()));
        }
 
 
        try {
            String str = fis.readLine();
            if (str == null) { // thefile doesn't have anything
                throw new IOException("Index file for the log of " + taskId
                        + "is empty.");
            }
            String loc = str.substring(str.indexOf(LogFileDetail.LOCATION)
                    + LogFileDetail.LOCATION.length());
            File tf = new File(loc, type.toString());
            return tf.exists() && tf.canRead();
 
 
        } finally {
            if (fis != null)
                fis.close();
        }
    }
 
 
}

從logdir中判斷是否有syslog。

 

Workaround:

查詢時加入在url上加入filter=SYSLOG就可以看到,不需要修改代碼。