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https://issues.apache.org/jira/browse/HIVE-6430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13963192#comment-13963192
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Sergey Shelukhin commented on HIVE-6430:
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Tested the patch on real queries. I do see huge memory reduction (modified
TPCDS query 72, worst map task goes from 7Gb to ~1.2Gb dump after populating
hash tables, I'll need to download the dumps to analyze but it's pretty clear
cut); and GC time counter goes down from ~1min total to few seconds, as
expected, but I also see huge wall clock time increase (without corresponding
CPU time increase it looks like) during processing. I would expect some
tradeoff but not as much as I'm seeing... will profile more.
> MapJoin hash table has large memory overhead
> --------------------------------------------
>
> Key: HIVE-6430
> URL: https://issues.apache.org/jira/browse/HIVE-6430
> Project: Hive
> Issue Type: Improvement
> Reporter: Sergey Shelukhin
> Assignee: Sergey Shelukhin
> Attachments: HIVE-6430.01.patch, HIVE-6430.02.patch,
> HIVE-6430.03.patch, HIVE-6430.04.patch, HIVE-6430.05.patch,
> HIVE-6430.06.patch, HIVE-6430.patch
>
>
> Right now, in some queries, I see that storing e.g. 4 ints (2 for key and 2
> for row) can take several hundred bytes, which is ridiculous. I am reducing
> the size of MJKey and MJRowContainer in other jiras, but in general we don't
> need to have java hash table there. We can either use primitive-friendly
> hashtable like the one from HPPC (Apache-licenced), or some variation, to map
> primitive keys to single row storage structure without an object per row
> (similar to vectorization).
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