You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@hive.apache.org by "Lefty Leverenz (JIRA)" <ji...@apache.org> on 2014/06/08 10:57:01 UTC
[jira] [Commented] (HIVE-6429) MapJoinKey has large memory overhead
in typical cases
[ 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.
--
This message was sent by Atlassian JIRA
(v6.2#6252)