[jira] [Commented] (HIVE-6643) Add a check for cross products in plans and output a warning

["Harish Butani (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-6643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13932668#comment-13932668 ] 

Harish Butani commented on HIVE-6643:
-------------------------------------

preliminary patch attached. There are some issues with this:
- for MapJoins: the warning only shows the bigTable (even this is not available). Hopefully the Vertex/Stage and Operator information  is enough for the user to see where the cross product is happening.
- for Shuffle Joins: we need the HIVE-4293 changes to show the tables in a Reducer that has more than 1 input.
- the .q.out files have the warnings, but these are appearing before the preehooks for the queries. Is this ok? 

> Add a check for cross products in plans and output a warning
> ------------------------------------------------------------
>
>                 Key: HIVE-6643
>                 URL: https://issues.apache.org/jira/browse/HIVE-6643
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Harish Butani
>            Assignee: Harish Butani
>         Attachments: HIVE-6643.1.patch
>
>
> Now that we support old style join syntax, it is easy to write queries that generate a plan with a cross product.
> For e.g. say you have A join B join C join D on A.x = B.x and A.y = D.y and C.z = D.z
> So the JoinTree is:
> A — B
> |__  D — C
> Since we don't reorder join graphs, we will end up with a cross product between (A join B) and C



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