Junping Du created MAPREDUCE-6852:
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Summary: 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
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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