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，

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();
}
}

}

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。