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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6430) MapJoin hash table has large memory overhead
Date Fri, 13 Jun 2014 23:33:01 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14031334#comment-14031334
] 

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

We don't have a way to add parameters to the wiki automatically.  Yes, they're in the template
file and I've got them on my wiki to-do list, but feel free to take care of them yourself
if you have time.

Mapjoin parameters don't have a section of their own, but they're listed together in order
of Hive release (except for a couple of hive.skewjoin.mapjoin parameters) so these belong
after hive.mapjoin.lazy.hashtable:

* [hive.mapjoin.lazy.hashtable | https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.mapjoin.lazy.hashtable]

> 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
>              Labels: TODOC14
>             Fix For: 0.14.0
>
>         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-6430.11.patch, HIVE-6430.12.patch, HIVE-6430.12.patch, HIVE-6430.13.patch,
HIVE-6430.14.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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