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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-963) no out of memory errors for skewed join
Date Fri, 04 Dec 2009 01:07:20 GMT

    [ https://issues.apache.org/jira/browse/HIVE-963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12785691#action_12785691
] 

Namit Jain commented on HIVE-963:
---------------------------------

Yes, that makes sense. I think 2 discussions are happening on this jira - in general it is
a good idea to have a cache on top of JDBM, and not write every row to a file.
That should speed up the mapper considerably for map-joins.

However, for a join happening on the reducer, JDBM seems too heavy weight to use.

> no out of memory errors for skewed join
> ---------------------------------------
>
>                 Key: HIVE-963
>                 URL: https://issues.apache.org/jira/browse/HIVE-963
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Ning Zhang
>
> Currently, in case of skew, hive runs out of memory.
> A simpler fix would be to use JDBM to store data and use that.
> It can be configurable and JDBM should only be triggered if the number of values for
a given key exceed a given number.

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