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https://issues.apache.org/jira/browse/HADOOP-1535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508784
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Devaraj Das commented on HADOOP-1535:
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Pls update the patch to stick to the 80 column boundary for the lines there.
> Wrong comparator used to merge files in Reduce phase
> ----------------------------------------------------
>
> Key: HADOOP-1535
> URL: https://issues.apache.org/jira/browse/HADOOP-1535
> Project: Hadoop
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.12.3, 0.13.0
> Reporter: Vivek Ratan
> Assignee: Vivek Ratan
> Fix For: 0.14.0
>
> Attachments: 1535_01.patch
>
>
> As per the fix for HADOOP-485, we allow users to optionally provide a
> different comparator to group values when calling the user's Reduce function.
> Devaraj and I were looking at the code yesterday and we found that in
> ReduceTask.java, we use the user-supplied comparator to merge the output
> files from the Map tasks (we use the user-supplied comparator when creating a
> new SequenceFile.Sorter object). This is incorrect as the comparator used to
> merge Map output files should be the same as that used to create those files
> in the Map phase. The user-supplied comparator for grouping values should be
> used only in the iterator passed to the user's Reduce function (which is done
> correctly in the code).
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