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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-2146) Block Sampling should adjust number of reducers accordingly to make it useful
Date Fri, 06 May 2011 08:01:04 GMT

    [ https://issues.apache.org/jira/browse/HIVE-2146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13029816#comment-13029816
] 

Hudson commented on HIVE-2146:
------------------------------

Integrated in Hive-trunk-h0.20 #712 (See [https://builds.apache.org/hudson/job/Hive-trunk-h0.20/712/])
    

> Block Sampling should adjust number of reducers accordingly to make it useful
> -----------------------------------------------------------------------------
>
>                 Key: HIVE-2146
>                 URL: https://issues.apache.org/jira/browse/HIVE-2146
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Siying Dong
>            Assignee: Siying Dong
>             Fix For: 0.8.0
>
>         Attachments: HIVE-2146.1.patch, HIVE-2146.2.patch
>
>
> Now number of reducers of block sampling is not modified, so that queries like:
> select c from tab tablesample(1 percent) group by c;
> can generate huge number of reducers although the input is sampled to be small.
> We need to shrink number of reducers to make block sampling more useful.
> Since now number of reducers are determined before get splits, the way to do it probably
is not clean enough, but we can do a good guess.

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