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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 Sun, 08 Jun 2014 08:57:01 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14021158#comment-14021158
] 

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

Just for the record, *hive.mapjoin.optimized.keys* is documented in the wiki with the description
added to hive-default.xml.template by HIVE-6188:

bq. Whether MapJoin hashtable should use optimized (size-wise) keys, allowing the table to
take less memory. Depending on key, the memory savings for entire table can be 5-15% or so.

* [patch for HIVE-6188 | https://issues.apache.org/jira/secure/attachment/12637478/HIVE-6188.patch]
* [Configuration Properties -- hive.mapjoin.optimized.keys | https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.mapjoin.optimized.keys]

> 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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