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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6430) MapJoin hash table has large memory overhead
Date Sun, 27 Apr 2014 06:50:14 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13982207#comment-13982207
] 

Lefty Leverenz commented on HIVE-6430:
--------------------------------------

This adds *hive.mapjoin.optimized.hashtable* and *hive.mapjoin.optimized.hashtable.wbsize*
to HiveConf.java.  They both need descriptions -- I assume "wb" means write buffer.

The descriptions can go in HiveConf comments or a release note for now, or you can patch hive-default.xml.template
and I'll add a comment on HIVE-6586 (for HIVE-6037, Synchronize HiveConf with hive-default.xml.template
and support show conf).

> 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-6430.07.patch, HIVE-6430.08.patch, HIVE-6430.09.patch,
HIVE-6430.10.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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