George Datskos created MAPREDUCE-4490:
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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.
{quote}
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)
{quote}
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 LinuxTaskController).
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 method
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