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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-12963) LIMIT statement with SORT BY creates additional MR job with hardcoded only one reducer
Date Sat, 30 Apr 2016 01:12:12 GMT

    [ https://issues.apache.org/jira/browse/HIVE-12963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15265038#comment-15265038
] 

Lefty Leverenz commented on HIVE-12963:
---------------------------------------

Doc note:  This adds *hive.groupby.limit.extrastep* to HiveConf.java, so it needs to be documented
in the wiki for release 2.1.0.

* [Configuration Properties -- Query and DDL Execution | https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-QueryandDDLExecution]

> LIMIT statement with SORT BY creates additional MR job with hardcoded only one reducer
> --------------------------------------------------------------------------------------
>
>                 Key: HIVE-12963
>                 URL: https://issues.apache.org/jira/browse/HIVE-12963
>             Project: Hive
>          Issue Type: Bug
>          Components: Hive
>    Affects Versions: 1.0.0, 1.2.1, 0.13
>            Reporter: Alina Abramova
>            Assignee: Alina Abramova
>              Labels: TODOC2.1
>             Fix For: 2.1.0
>
>         Attachments: HIVE-12963.1.patch, HIVE-12963.2.patch, HIVE-12963.3.patch, HIVE-12963.4.patch,
HIVE-12963.6.patch
>
>
> I execute query:
> hive> select age from test1 sort by age.age  limit 10;                      
> Total jobs = 2
> Launching Job 1 out of 2
> Number of reduce tasks not specified. Estimated from input data size: 1
> Launching Job 2 out of 2
> Number of reduce tasks determined at compile time: 1
> When I have a large number of rows then the last stage of the job takes a long time.
I think we could allow to user choose number of reducers of last job or refuse extra MR job.
> The same behavior I observed with querie:
> hive> create table new_test as select age from test1 group by age.age  limit 10;



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