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From Sameer Joshi <sameer.jo...@serenesoftware.com>
Subject java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap
Date Wed, 28 Jul 2010 01:12:23 GMT
I installed Java and Hadoop on a GoGrid cloud server using Red Hat
Enterprise Linux Server release 5.1 (Tikanga). Hadoop installed fine and
starts fine, however I get an error (java.lang.NullPointerException at
java.util.concurrent.ConcurrentHashMap) while running the Hadoop wordcount
example. My guess was that this was a localhost or IPv6 issue.

* I have tested replacing 'localhost' with both the local IP, and server IP
addresses (when out of options) in Hadoop conf
* I have disabled IPv6 both in sysctl.conf and hadoop-env.sh (former
followed by a server restart)

Any thoughts?
Thank you.


The output is given below

# bin/hadoop jar hadoop-0.20.2-examples.jar wordcount datasets tests/out7
10/07/27 05:44:59 INFO input.FileInputFormat: Total input paths to process :
1
10/07/27 05:44:59 INFO mapred.JobClient: Running job: job_201007270544_0001
10/07/27 05:45:00 INFO mapred.JobClient: map 0% reduce 0%
10/07/27 05:45:12 INFO mapred.JobClient: map 100% reduce 0%
10/07/27 05:45:17 INFO mapred.JobClient: Task Id :
attempt_201007270544_0001_r_000000_0, Status : FAILED

Error: java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(Unknown Source)
at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)


10/07/27 05:45:24 INFO mapred.JobClient: Task Id :
attempt_201007270544_0001_r_000000_1, Status : FAILED
Error: java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(Unknown Source)
at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)


10/07/27 05:45:30 INFO mapred.JobClient: Task Id :
attempt_201007270544_0001_r_000000_2, Status : FAILED
Error: java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(Unknown Source)
at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)


10/07/27 05:45:39 INFO mapred.JobClient: Job complete: job_201007270544_0001

10/07/27 05:45:39 INFO mapred.JobClient: Counters: 12
10/07/27 05:45:39 INFO mapred.JobClient: Job Counters
10/07/27 05:45:39 INFO mapred.JobClient: Launched reduce tasks=4
10/07/27 05:45:39 INFO mapred.JobClient: Launched map tasks=1
10/07/27 05:45:39 INFO mapred.JobClient: Data-local map tasks=1
10/07/27 05:45:39 INFO mapred.JobClient: Failed reduce tasks=1
10/07/27 05:45:39 INFO mapred.JobClient: FileSystemCounters
10/07/27 05:45:39 INFO mapred.JobClient: HDFS_BYTES_READ=15319
10/07/27 05:45:39 INFO mapred.JobClient: FILE_BYTES_WRITTEN=12847
10/07/27 05:45:39 INFO mapred.JobClient: Map-Reduce Framework
10/07/27 05:45:39 INFO mapred.JobClient: Combine output records=934
10/07/27 05:45:39 INFO mapred.JobClient: Map input records=149
10/07/27 05:45:39 INFO mapred.JobClient: Spilled Records=934
10/07/27 05:45:39 INFO mapred.JobClient: Map output bytes=25346
10/07/27 05:45:39 INFO mapred.JobClient: Combine input records=2541
10/07/27 05:45:39 INFO mapred.JobClient: Map output records=2541

-- 
Dr. Sameer Joshi, Ph.D.
Senior computer scientist,
Serene Software.

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