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From "Zoltan Haindrich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-19824) Improve online datasize estimations for MapJoins
Date Fri, 08 Jun 2018 07:00:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-19824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16505773#comment-16505773
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Zoltan Haindrich commented on HIVE-19824:
-----------------------------------------

[~sershe] it's {{BytesBytesMultiHashMap}} - I think that's in service most of the time...
The source of the problem is that the estimation have entirely ignored the overhead of storing
the rows..

> 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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