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