[jira] Resolved: (HIVE-988) mapjoin should throw an error if the input is too large

["Namit Jain (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-988?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Namit Jain resolved HIVE-988.
-----------------------------

      Resolution: Fixed
    Hadoop Flags: [Reviewed]

> 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, HIVE-988_3.patch, HIVE-988_4.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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