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https://issues.apache.org/jira/browse/HIVE-6429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13909268#comment-13909268
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Lefty Leverenz commented on HIVE-6429:
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*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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