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From Paolo Castagna <castagna.li...@googlemail.com>
Subject NullPointerException when running multiple reducers with Hadoop 0.22.0-SNAPSHOT
Date Tue, 28 Jun 2011 17:04:30 GMT
Hi,
I am using Apache Whirr to setup an Hadoop cluster on EC2 using Hadoop
0.22.0 SNAPSHOTs (nightly) builds from Jenkins. For details, see [1,2].
(Is there a better place where I can get nightly builds for Hadoop?)

I have a Reducer which does not emit any (key,value) pairs (it generates
only side effect files). When I run using only one reducer everything seems
fine. If I setup multiple reducers, each one generating different side effect
files, I get a NullPointerException:

 WARN  Exception running child : java.lang.NullPointerException
   at org.apache.hadoop.mapred.TaskLogAppender.flush(TaskLogAppender.java:96)
   at org.apache.hadoop.mapred.TaskLog.syncLogs(TaskLog.java:239)
   at org.apache.hadoop.mapred.Child$4.run(Child.java:225)
   at java.security.AccessController.doPrivileged(Native Method)
   at javax.security.auth.Subject.doAs(Subject.java:396)
   at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1153)
   at org.apache.hadoop.mapred.Child.main(Child.java:217)

Have you ever seen this exception/stacktrace?

My driver is here [3] and the reducer is here [4].

Any help?

Regards,
Paolo

 [1] https://github.com/castagna/tdbloader3/blob/master/hadoop-ec2.properties
 [2] https://builds.apache.org/view/G-L/view/Hadoop/job/Hadoop-22-Build/lastSuccessfulBuild/artifact/hadoop-0.22.0-SNAPSHOT.tar.gz
 [3] https://github.com/castagna/tdbloader3/blob/master/src/main/java/com/talis/labs/tdb/tdbloader3/ThirdDriver.java
 [4] https://github.com/castagna/tdbloader3/blob/master/src/main/java/com/talis/labs/tdb/tdbloader3/ThirdReducer.java


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