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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-988) mapjoin should throw an error if the input is too large
Date Wed, 06 Jan 2010 05:43:54 GMT

    [ https://issues.apache.org/jira/browse/HIVE-988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12796995#action_12796995
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Ning Zhang commented on HIVE-988:
---------------------------------

The mapper will finish but it doesn't mean it succeed. The boolean variable fatalError indicates
there is an fatal error occurred. I can change this to use the boolean variable done, but
it may be confused with the case where the job succeeded. 

Yes, there may be race condition. I guess we can check the counter again (if fatal is false)
outside the while loop when rj is completed. 

> mapjoin should throw an error if the input is too large
> -------------------------------------------------------
>
>                 Key: HIVE-988
>                 URL: https://issues.apache.org/jira/browse/HIVE-988
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Ning Zhang
>             Fix For: 0.5.0
>
>         Attachments: HIVE-988.patch, HIVE-988_2.patch
>
>
> If the input to the map join is larger than a specific threshold, it may lead to a very
slow execution of the join.
> It is better to throw an error, and let the user redo his query as a non map-join query.
> However, the current map-reduce framework will retry the mapper 4 times before actually
killing the job.
> Based on a offline discussion with Dhruba, Ning and myself, we came up with the following
algorithm:
> Keep a threshold in the mapper for the number of rows to be processed for map-join. If
the number of rows
> exceeds that threshold, set a counter and kill that mapper.
> The client (ExecDriver) monitors that job continuously - if this counter is set, it kills
the job and also
> shows an appropriate error message to the user, so that he can retry the query without
the map join.

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