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https://issues.apache.org/jira/browse/HADOOP-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12773008#action_12773008
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Amar Kamat commented on HADOOP-6357:
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Amazing!!
> Reducers fail with OutOfMemoryError while copying Map outputs
> -------------------------------------------------------------
>
> Key: HADOOP-6357
> URL: https://issues.apache.org/jira/browse/HADOOP-6357
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 0.20.0
> Reporter: Chandra Prakash Bhagtani
> Fix For: 0.20.0
>
> Attachments: HADOOP-6357.patch
>
>
> Reducers fail while copying Map outputs with following exception
> java.lang.OutOfMemoryError: Java heap space at
> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.shuffleInMemory(ReduceTask.java:1539)
> at
> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.getMapOutput(ReduceTask.java:1432)
> at
> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:1285)
> at
> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:1216)
> ,Error:
> Reducer's memory usage keeps on increasing and ultimately exceeds -Xmx value
> I even tried with -Xmx6.5g to each reducer but it's still failing
> While looking into the reducer logs, I found that reducers were doing
> shuffleInMemory every time, rather than doing shuffleOnDisk
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