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From Pengcheng Xiong <pxi...@apache.org>
Subject Re: Num Rows computed by EXPLAIN - Hive
Date Thu, 09 Feb 2017 07:12:25 GMT
Did u run "analyze table emp compute statistics" before you run the
explain? thanks.

Pengcheng

On Wed, Feb 8, 2017 at 9:29 PM, Vivek Sharma <vlsharma@hotmail.com> wrote:

> Hi,
>
>
> I am new to Hive (just few days of learning).
>
>
> I am an Oracle Performance Expert and am comparing the Explain feature of
> Hive with Oracle Explain Plan command. I have an Internal Table with around
> 100 Rows in it. However, the Explain command in Hive computes this as 33,
> which looks to be huge discrepancy and cause a performance issues (for a
> larger table). Wanted to know the internal calculations of Hive to come out
> with the NUM ROWS. The output is pasted below (The table actually has 100
> Rows) :
>
>
> hive (vivek)> explain select country, empno from emp;
> OK
> Explain
> STAGE DEPENDENCIES:
>   Stage-0 is a root stage
>
> STAGE PLANS:
>   Stage: Stage-0
>     Fetch Operator
>       limit: -1
>       Processor Tree:
>         TableScan
>           alias: emp
>           Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE
> Column stats: NONE
>           Select Operator
>             expressions: country (type: string), empno (type: int)
>             outputColumnNames: _col0, _col1
>             Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE
> Column stats: NONE
>             ListSink
>
> Regards
> Vivek
>
>

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