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https://issues.apache.org/jira/browse/HIVE-6429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14047295#comment-14047295
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Lefty Leverenz commented on HIVE-6429:
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Added comment to HIVE-6586 so the description of *hive.mapjoin.optimized.keys*
won't get lost in the shuffle when HIVE-6037 changes HiveConf.java.
> 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
> Fix For: 0.13.0
>
> Attachments: HIVE-6429.01.patch, HIVE-6429.02.patch,
> HIVE-6429.03.patch, HIVE-6429.04.patch, HIVE-6429.05.patch,
> HIVE-6429.06.patch, HIVE-6429.07.patch, HIVE-6429.08.patch,
> HIVE-6429.09.patch, HIVE-6429.10.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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