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Date: Tue, 10 Nov 2015 17:10:11 +0000 (UTC)
From: "Jesus Camacho Rodriguez (JIRA)" <jira@apache.org>
To: issues@hive.apache.org
Message-ID: <JIRA.12902146.1443800461000.29136.1447175411516@Atlassian.JIRA>
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Subject: [jira] [Commented] (HIVE-12017) Do not disable CBO by default when
 number of joins in a query is equal or less than 1
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    [ https://issues.apache.org/jira/browse/HIVE-12017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14998913#comment-14998913 ] 

Jesus Camacho Rodriguez commented on HIVE-12017:
------------------------------------------------

Thanks a lot for the comments [~ashutoshc] and for categorizing the changes.

1) should not be a big issue, at least for the moment.
3) should be an issue only if it is really a performance loss. For instance, I check some plans and what was happening was that transitive propagation was more advanced in Calcite, thus we were pruning both join inputs and we ended up with a cartesian product.

I agree 2) and 5) are specially concerning, since they lead to correctness issues; I'll explore those ones further and update the issue/create new issues.

At least the fixes to correctness issues should be checked in before applying this patch.

> Do not disable CBO by default when number of joins in a query is equal or less than 1
> -------------------------------------------------------------------------------------
>
>                 Key: HIVE-12017
>                 URL: https://issues.apache.org/jira/browse/HIVE-12017
>             Project: Hive
>          Issue Type: Improvement
>          Components: CBO
>    Affects Versions: 2.0.0
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Jesus Camacho Rodriguez
>         Attachments: HIVE-12017.01.patch, HIVE-12017.02.patch, HIVE-12017.03.patch, HIVE-12017.04.patch, HIVE-12017.05.patch, HIVE-12017.06.patch, HIVE-12017.07.patch, HIVE-12017.08.patch
>
>
> Instead, we could disable some parts of CBO that are not relevant if the query contains 1 or 0 joins. Implementation should be able to define easily other query patterns for which we might disable some parts of CBO (in case we want to do it in the future).


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