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https://issues.apache.org/jira/browse/HADOOP-4158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630338#action_12630338
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Zheng Shao commented on HADOOP-4158:
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Agree. This applies to the hash-based (multiple) group by I guess, because the
sort-based (single) group by already pre-compute the target key and aggregation
columns so only those that are necessary are passed.
> [hive] redundant columns being passed in group by stage 1
> ---------------------------------------------------------
>
> Key: HADOOP-4158
> URL: https://issues.apache.org/jira/browse/HADOOP-4158
> Project: Hadoop Core
> Issue Type: Bug
> Components: contrib/hive
> Reporter: Namit Jain
> Assignee: Namit Jain
>
> In the first map-reduce stage, all input columns are copied currently.
> Instead, we should walk over the filter and projections for that destination
> and only copy columns which occur there
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