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From "Zoltan Haindrich (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-18108) in case basic stats are missing; rowcount estimation depends on the selected columns size
Date Fri, 22 Dec 2017 16:36:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-18108?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zoltan Haindrich updated HIVE-18108:
------------------------------------
    Attachment: HIVE-18108.03.patch

> in case basic stats are missing; rowcount estimation depends on the selected columns
size
> -----------------------------------------------------------------------------------------
>
>                 Key: HIVE-18108
>                 URL: https://issues.apache.org/jira/browse/HIVE-18108
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>         Attachments: HIVE-18108.01.patch, HIVE-18108.02.patch, HIVE-18108.02wip02.patch,
HIVE-18108.03.patch
>
>
> in case basicstats are not available (especially rowcount):
> {code}
> set hive.stats.autogather=false;
> create table t (a integer, b string);
> insert into t values (1,'asd1');
> insert into t values (2,'asd2');
> insert into t values (3,'asd3');
> insert into t values (4,'asd4');
> insert into t values (5,'asd5');
> explain select a,count(1) from t group by a;
> -- estimated to read 8 rows from table t
> explain select b,count(1) from t group by b;
> -- estimated: 1 rows
> explain select a,b,count(1) from t group by a,b;
> -- estimated: 1 rows
> {code}
> it may not depend on the actually selected column set.



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