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Posted to common-dev@hadoop.apache.org by "Namit Jain (JIRA)" <ji...@apache.org> on 2008/10/15 08:25:44 UTC

[jira] Created: (HADOOP-4415) [Hive] group by over a subquery with a cluster by not optimized

[Hive] group by over a subquery with a cluster by not optimized
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                 Key: HADOOP-4415
                 URL: https://issues.apache.org/jira/browse/HADOOP-4415
             Project: Hadoop Core
          Issue Type: Bug
          Components: contrib/hive
            Reporter: Namit Jain
            Assignee: Namit Jain


Consider the following


select x.a, count(x.b) from (select ...... cluster by a) x group by x.a


Even though the user has specifically asked to cluster by a, the group by will again run 2 map-reduce jobs,
sorting by a random number and a in that order. So, there will be a total of 3 map-reduce jobs sorting
by a, random and a respectively - this should be optimized

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