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From "Kevin Wilfong (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-3496) Query plan for multi-join where the third table joined is a subquery containing a map-only union with hive.auto.convert.join=true is wrong
Date Fri, 21 Sep 2012 02:27:07 GMT

     [ https://issues.apache.org/jira/browse/HIVE-3496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kevin Wilfong updated HIVE-3496:
--------------------------------

    Attachment: HIVE-3496.1.patch.txt
    
> Query plan for multi-join where the third table joined is a subquery containing a map-only
union with hive.auto.convert.join=true is wrong
> ------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-3496
>                 URL: https://issues.apache.org/jira/browse/HIVE-3496
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.10.0
>            Reporter: Kevin Wilfong
>            Assignee: Kevin Wilfong
>             Fix For: 0.10.0
>
>         Attachments: HIVE-3496.1.patch.txt
>
>
> Take the following query as an example:
> EXPLAIN SELECT * FROM 
> src11 a JOIN
> src12 b ON (a.key = b.key) JOIN
> (SELECT * FROM (SELECT * FROM src13 UNION ALL SELECT * FROM src14)a )c ON c.value = b.value;
> When hive.auto.convert.join=true, the two joins are implemented separately as conditional
tasks with two mapjoins and a backup common join.  In the second join, the conditional task
will be a backup task, contained in the ConditionalTask, and a root task.  This is clearly
wrong, and leads to query failures.
> I've traced this to the joinUnionPlan method of GenMapRedUtils.  If the union operator
was performed in its own map reduce task and it could be a root task, when it is added to
the mapper of the existing task which performs the join in the reducer, this task will get
made a root task without first checking if the existing (non-union) task has any dependencies.

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