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From "George Datskos (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4490) JVM reuse is incompatible with LinuxTaskController (and therefore incompatible with Security)
Date Fri, 27 Jul 2012 01:23:33 GMT
George Datskos created MAPREDUCE-4490:

             Summary: JVM reuse is incompatible with LinuxTaskController (and therefore incompatible
with Security)
                 Key: MAPREDUCE-4490
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4490
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: task-controller, tasktracker
    Affects Versions: 1.0.3
            Reporter: George Datskos

When using LinuxTaskController, JVM reuse (mapred.job.reuse.jvm.num.tasks > 1) with more
map tasks in a job than there are map slots in the cluster will result in immediate task failures
for the second task in each JVM (and then the JVM exits). We have investigated this bug and
the root cause is as follows. When using LinuxTaskController, the userlog directory for a
task attempt (../userlogs/job/task-attempt) is created only on the first invocation (when
the JVM is launched) because userlogs directories are created by the task-controller binary
which only runs *once* per JVM. Therefore, attempting to create log.index is guaranteed to
fail with ENOENT leading to immediate task failure and child JVM exit.

2012-07-24 14:29:11,914 INFO org.apache.hadoop.mapred.TaskLog: Starting logging for a new
task attempt_201207241401_0013_m_000027_0 in the same JVM as that of the first task /var/log/hadoop/mapred/userlogs/job_201207241401_0013/attempt_201207241401_0013_m_000006_0
2012-07-24 14:29:11,915 WARN org.apache.hadoop.mapred.Child: Error running child
ENOENT: No such file or directory
        at org.apache.hadoop.io.nativeio.NativeIO.open(Native Method)
        at org.apache.hadoop.io.SecureIOUtils.createForWrite(SecureIOUtils.java:161)
        at org.apache.hadoop.mapred.TaskLog.writeToIndexFile(TaskLog.java:296)
        at org.apache.hadoop.mapred.TaskLog.syncLogs(TaskLog.java:369)
        at org.apache.hadoop.mapred.Child.main(Child.java:229)

The above error occurs in a JVM which runs tasks 6 and 27.  Task6 goes smoothly. Then Task27
starts. The directory /var/log/hadoop/mapred/userlogs/job_201207241401_0013/attempt_201207241401_0013_m_0000027_0
is never created so when mapred.Child tries to write the log.index file for Task27, it fails
with ENOENT because the attempt_201207241401_0013_m_0000027_0 directory does not exist. Therefore,
the second task in each JVM is guaranteed to fail (and then the JVM exits) every time when
using LinuxTaskController. Note that this problem does not occur when using the DefaultTaskController
because the userlogs directories are created for each task (not just for each JVM as with

For each task, the TaskRunner calls the TaskController's createLogDir method before attempting
to write out an index file.

* DefaultTaskController#createLogDir: creates log directory for each task
* LinuxTaskController#createLogDir: does nothing
** task-controller binary creates log directory [create_attempt_directories] (but only for
the first task)

Possible Solution: add a new command to task-controller *initialize task* to create attempt
directories.  Call that command, with ShellCommandExecutor, in the LinuxTaskController#createLogDir

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