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From "Jesus Camacho Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-15023) SimpleFetchOptimizer needs to optimize limit=0
Date Thu, 20 Oct 2016 08:03:58 GMT

    [ https://issues.apache.org/jira/browse/HIVE-15023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15591142#comment-15591142
] 

Jesus Camacho Rodriguez commented on HIVE-15023:
------------------------------------------------

I checked a bit further the code and I think the approach I propose above might not be as
simple as I thought, since we would need to create the task and thus it is not simply moving
the clause from one place to another...

I think it is OK then to proceed, but if we leave the fix as it is now, please add a comment
to the new _if_ statement in SimpleFetchOptimizer explaining why we are bailing out there.
Thanks

> SimpleFetchOptimizer needs to optimize limit=0
> ----------------------------------------------
>
>                 Key: HIVE-15023
>                 URL: https://issues.apache.org/jira/browse/HIVE-15023
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Pengcheng Xiong
>            Assignee: Pengcheng Xiong
>         Attachments: HIVE-15023.01.patch
>
>
> on current master
> {code}
> hive> explain select key from src limit 0;
> OK
> STAGE DEPENDENCIES:
>   Stage-0 is a root stage
> STAGE PLANS:
>   Stage: Stage-0
>     Fetch Operator
>       limit: 0
>       Processor Tree:
>         TableScan
>           alias: src
>           Statistics: Num rows: 500 Data size: 5312 Basic stats: COMPLETE Column stats:
NONE
>           Select Operator
>             expressions: key (type: string)
>             outputColumnNames: _col0
>             Statistics: Num rows: 500 Data size: 5312 Basic stats: COMPLETE Column stats:
NONE
>             Limit
>               Number of rows: 0
>               Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column stats: NONE
>               ListSink
> Time taken: 7.534 seconds, Fetched: 20 row(s)
> {code}



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