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Date: Wed, 4 May 2011 00:46:03 +0000 (UTC)
From: "Ning Zhang (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
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Subject: [jira] [Updated] (HIVE-2146) Block Sampling should adjust number of
 reducers accordingly to make it useful
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     [ https://issues.apache.org/jira/browse/HIVE-2146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ning Zhang updated HIVE-2146:
-----------------------------

    Status: Open  (was: Patch Available)

> 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
>         Attachments: HIVE-2146.1.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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