[jira] [Assigned] (HIVE-8625) Some union queries result in plans with many unions with CBO on

["Jesús Camacho Rodríguez (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-8625?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jesús Camacho Rodríguez reassigned HIVE-8625:
---------------------------------------------

    Assignee: Jesús Camacho Rodríguez

> Some union queries result in plans with many unions with CBO on
> ---------------------------------------------------------------
>
>                 Key: HIVE-8625
>                 URL: https://issues.apache.org/jira/browse/HIVE-8625
>             Project: Hive
>          Issue Type: Bug
>          Components: CBO
>    Affects Versions: 0.14.0
>            Reporter: Jesús Camacho Rodríguez
>            Assignee: Jesús Camacho Rodríguez
>            Priority: Minor
>             Fix For: 0.14.0
>
>         Attachments: HIVE-8625.patch
>
>
> For some queries e.g. union9, union16, we are getting plans with many binary unions when CBO is on. The reason is that an identity select operator is introduced after each union by the CBO; thus, the method that was merging the unions when the translation of the AST into a logical plan was being done is not executed, as it does not detect there is another union operator. 
> With the fix in the patch attached, the method will merge the two unions if (1) one is the child of the other one, or (2) if one is a descendant of the other one and there is an identity select operator between them.



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