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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6429) MapJoinKey has large memory overhead in typical cases
Date Sat, 22 Feb 2014 06:42:19 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13909268#comment-13909268
] 

Lefty Leverenz commented on HIVE-6429:
--------------------------------------

*hive.mapjoin.optimized.keys* needs a definition ... but I'm not sure where, because that
depends on the state of HIVE-6037 which will put the config param definitions into HiveConf.java
and then generate hive-default.xml.template from HiveConf.java.

See comment on HIVE-6455 for details (but note that HIVE-6037 has been reopened):  [17 Feb
2014 22:26 comment |https://issues.apache.org/jira/browse/HIVE-6455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13903744#comment-13903744].

So if this commits before HIVE-6037, *hive.mapjoin.optimized.keys* should be documented in
hive-default.xml.template as usual but if it commits after HIVE-6037 a definition should be
added to the patched version of HiveConf.java.  In any case, I'll add it to the wiki with
a release note.



> MapJoinKey has large memory overhead in typical cases
> -----------------------------------------------------
>
>                 Key: HIVE-6429
>                 URL: https://issues.apache.org/jira/browse/HIVE-6429
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>         Attachments: HIVE-6429.01.patch, HIVE-6429.02.patch, HIVE-6429.03.patch, HIVE-6429.WIP.patch,
HIVE-6429.patch
>
>
> The only thing that MJK really needs it hashCode and equals (well, and construction),
so there's no need to have array of writables in there. Assuming all the keys for a table
have the same structure, for the common case where keys are primitive types, we can store
something like a byte array combination of keys to reduce the memory usage. Will probably
speed up compares too.



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