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https://issues.apache.org/jira/browse/HIVE-19824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16505554#comment-16505554
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Sergey Shelukhin commented on HIVE-19824:
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Which hashmap is that? I thought our custom hashmap should have much less
overhead.
> Improve online datasize estimations for MapJoins
> ------------------------------------------------
>
> Key: HIVE-19824
> URL: https://issues.apache.org/jira/browse/HIVE-19824
> Project: Hive
> Issue Type: Improvement
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
> Attachments: HIVE-19824.01wip01.patch, HIVE-19824.01wip01.patch
>
>
> Statistics.datasize() only accounts for "real" data size; but for example
> handling 1M rows might introduce some datastructure overhead...if the "real"
> data is small - even this overhead might become the real memory usage
> for 6.5M rows of (int,int) the estimation is 52MB
> in reality this eats up ~260MB from which 210MB is used to service the
> hashmap functionality to that many rows.
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