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From "Junping Du (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-6852) Job#updateStatus() failed with NPE due to race condition
Date Wed, 01 Mar 2017 00:50:45 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-6852?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Junping Du updated MAPREDUCE-6852:
----------------------------------
    Attachment: MAPREDUCE-6852-v2.patch

Sounds reasonable. v2 patch incorporate comments here.

> Job#updateStatus() failed with NPE due to race condition
> --------------------------------------------------------
>
>                 Key: MAPREDUCE-6852
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6852
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Junping Du
>            Assignee: Junping Du
>         Attachments: MAPREDUCE-6852.patch, MAPREDUCE-6852-v2.patch
>
>
> Like MAPREDUCE-6762, we found this issue in a cluster where Pig query occasionally failed
on NPE - "Pig uses JobControl API to track MR job status, but sometimes Job History Server
failed to flush job meta files to HDFS which caused the status update failed." Beside NPE
in o.a.h.mapreduce.Job.getJobName, we also get NPE in Job.updateStatus() and the exception
is as following:
> {noformat}
> Caused by: java.lang.NullPointerException
> 	at org.apache.hadoop.mapreduce.Job$1.run(Job.java:323)
> 	at org.apache.hadoop.mapreduce.Job$1.run(Job.java:320)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at javax.security.auth.Subject.doAs(Subject.java:422)
> 	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1833)
> 	at org.apache.hadoop.mapreduce.Job.updateStatus(Job.java:320)
> 	at org.apache.hadoop.mapreduce.Job.isComplete(Job.java:604)
> {noformat}
> We found state here is null. However, we already check the job state to be RUNNING as
code below:
> {noformat}
>   public boolean isComplete() throws IOException {
>     ensureState(JobState.RUNNING);
>     updateStatus();
>     return status.isJobComplete();
>   }
> {noformat}
> The only possible reason here is two threads are calling here for the same time: ensure
state first, then one thread update the state to null while the other thread hit NPE issue
here.
> We should fix this NPE exception.



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