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https://issues.apache.org/jira/browse/HIVE-11761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14735564#comment-14735564
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Aihua Xu commented on HIVE-11761:
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That's correct. It's only for performance reason.
> DoubleWritable hashcode for GroupBy is not properly generated
> -------------------------------------------------------------
>
> Key: HIVE-11761
> URL: https://issues.apache.org/jira/browse/HIVE-11761
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Affects Versions: 1.2.0, 2.0.0
> Reporter: Aihua Xu
> Assignee: Aihua Xu
> Attachments: HIVE-11761.patch
>
>
> HIVE-11502 fixed the hashcode for LazyDouble. Additionally we should fix for
> DoubleWritable as well due to HADOOP-12217 issue. In some cases such as
> {{select avg(t) from (select * from over1k cross join src) t group by d;}}
> where d is double type, the data is actually in DoubleWritable, not
> LazyDouble. Thus, before HADOOP-12217 gets fixed, we need to fix hashcode for
> LazyDouble as well as DoubleWritable.
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