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From "Haohui Mai (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-5837) MRAppMaster fails when checking on uber mode
Date Tue, 15 Apr 2014 20:26:18 GMT
Haohui Mai created MAPREDUCE-5837:
-------------------------------------

             Summary: MRAppMaster fails when checking on uber mode
                 Key: MAPREDUCE-5837
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5837
             Project: Hadoop Map/Reduce
          Issue Type: Bug
            Reporter: Haohui Mai
            Assignee: Haohui Mai
            Priority: Critical
         Attachments: MAPREDUCE-5837.000.patch

When the MRAppMaster determines whether the job should run in the uber mode, it call {{Class.forName()}}
to check whether the class is derived from {{ChainMapper}}:

{code}
 try {
      String mapClassName = conf.get(MRJobConfig.MAP_CLASS_ATTR);
      if (mapClassName != null) {
        Class<?> mapClass = Class.forName(mapClassName);
        if (ChainMapper.class.isAssignableFrom(mapClass))
          isChainJob = true;
      }
    } catch (ClassNotFoundException cnfe) {
      // don't care; assume it's not derived from ChainMapper
    }
{code}

The problem here is that {{Class.forName()}} can also throw {{NoClassDefError}}. It happens
when the additional dependent jar is unavailable to the MRAppMaster. For example, the MRAppMaster
complains about a MR job on Scala:

{noformat}
2014-04-15 11:52:55,877 FATAL [main] org.apache.hadoop.mapreduce.v2.app.MRAppMaster: Error
starting MRAppMaster
java.lang.NoClassDefFoundError: scala/Function1
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:190)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl.isChainJob(JobImpl.java:1282)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl.makeUberDecision(JobImpl.java:1224)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl.access$3700(JobImpl.java:136)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl$InitTransition.transition(JobImpl.java:1425)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl$InitTransition.transition(JobImpl.java:1363)
        at org.apache.hadoop.yarn.state.StateMachineFactory$MultipleInternalArc.doTransition(StateMachineFactory.java:385)
        at org.apache.hadoop.yarn.state.StateMachineFactory.doTransition(StateMachineFactory.java:302)
        at org.apache.hadoop.yarn.state.StateMachineFactory.access$300(StateMachineFactory.java:46)
        at org.apache.hadoop.yarn.state.StateMachineFactory$InternalStateMachine.doTransition(StateMachineFactory.java:448)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl.handle(JobImpl.java:976)
        at org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl.handle(JobImpl.java:135)
        at org.apache.hadoop.mapreduce.v2.app.MRAppMaster$JobEventDispatcher.handle(MRAppMaster.java:1263)
        at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.serviceStart(MRAppMaster.java:1063)
        at org.apache.hadoop.service.AbstractService.start(AbstractService.java:193)
        at org.apache.hadoop.mapreduce.v2.app.MRAppMaster$1.run(MRAppMaster.java:1480)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:415)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1606)
        at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.initAndStartAppMaster(MRAppMaster.java:1476)
        at org.apache.hadoop.mapreduce.v2.app.MRAppMaster.main(MRAppMaster.java:1409)
Caused by: java.lang.ClassNotFoundException: scala.Function1
        at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
        ... 22 more
{noformat}
 
The proposed fix is to catch {{NoClassDefError}} at the corresponding places.



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