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From "Runping Qi (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-2164) Reducer sort failed due to wrong key class
Date Tue, 06 Nov 2007 21:49:50 GMT
Reducer sort failed due to wrong key class

                 Key: HADOOP-2164
                 URL: https://issues.apache.org/jira/browse/HADOOP-2164
             Project: Hadoop
          Issue Type: Bug
          Components: mapred
            Reporter: Runping Qi

One of my job's reducers failed due to the following exception:

java.io.IOException: wrong key class: class org.apache.hadoop.io.LongWritable is not class
	at org.apache.hadoop.io.SequenceFile$Sorter$SegmentDescriptor.nextRawKey(SequenceFile.java:2733)
	at org.apache.hadoop.io.SequenceFile$Sorter$MergeQueue.merge(SequenceFile.java:2542)
	at org.apache.hadoop.io.SequenceFile$Sorter.merge(SequenceFile.java:2326)
	at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:291)
	at org.apache.hadoop.mapred.TaskTracker$Child.main(TaskTracker.java:1760)

I checked the segment files to be merged on the node running the reducer, 
and founded that one of the map output file did record org.apache.hadoop.io.LongWritable as
its key class!
The question is how that happened? My job conf specified Text as the map output key class,
and other map output files had 
the correct key class!

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