RE: Application Master waits a long time after Mapper/Reducers finish

[Rohith Sharma K S]

Hi

From thread dump, it seems waiting for HDFS operation.  Can you attach AM logs, 
and do you see any client retry for connecting to HDFS?

"CommitterEvent Processor #4" prio=10 tid=0x000000000199a800 nid=0x18df in 
Object.wait() [0x00007f4f12aa4000]
   java.lang.Thread.State: WAITING (on object monitor)
                at java.lang.Object.wait(Native Method)
                at java.lang.Object.wait(Object.java:503)
                ……………………….
                at org.apache.hadoop.hdfs.DFSClient.rename(DFSClient.java:1864)
                at 
org.apache.hadoop.hdfs.DistributedFileSystem.rename(DistributedFileSystem.java:575)
                at 
org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter.mergePaths(FileOutputCommitter.java:345)
                at 
org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter.mergePaths(FileOutputCommitter.java:362)
                at 
org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter.commitJob(FileOutputCommitter.java:310)
                at 
org.apache.hadoop.mapreduce.v2.app.commit.CommitterEventHandler$EventProcessor.handleJobCommit(CommitterEventHandler.java:274)
                at 
org.apache.hadoop.mapreduce.v2.app.commit.CommitterEventHandler$EventProcessor.run(CommitterEventHandler.java:237)


May be you can check from HDFS that is it Healthy?

Thanks & Regards
Rohith Sharma K S

From: Ashish Kumar Singh [mailto:ashish23...@gmail.com]
Sent: 20 July 2015 14:16
To: user@hadoop.apache.org
Subject: Application Master waits a long time after Mapper/Reducers finish

Hello Users ,

I am facing a problem running Mapreduce jobs on Hadoop 2.6.
I am observing that the Applocation Master  waits for a long time after all the 
Mappers and Reducers are completed before the job is completed .

This wait time sometimes exceeds 20-25 mins which is very strange as our 
mappers and reducers complete in less than 10 minutes for the job .

Below are some observations:
a) Job completion status stands at 95% when the wait begins

b)JOB_COMMIT is initiated just before this wait time ( logs: 2015-07-14 
01:54:46,636 INFO [AsyncDispatcher event handler] 
org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: job_1436854849540_0123Job 
Transitioned from RUNNING to COMMITTING )

c) job success happens after 20-25 minutes ( logs: 2015-07-14 02:15:06,634 INFO 
[AsyncDispatcher event handler] 
org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: job_1436854849540_0123Job 
Transitioned from COMMITTING to SUCCEEDED )


Appreciate any help on this .

Thread dump while the Application master hangs is attached.
Regards,
Ashish