[jira] [Created] (HIVE-3952) merge map-job followed by map-reduce job

["Namit Jain (JIRA)" <ji...@apache.org>]

Namit Jain created HIVE-3952:
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             Summary: merge map-job followed by map-reduce job
                 Key: HIVE-3952
                 URL: https://issues.apache.org/jira/browse/HIVE-3952
             Project: Hive
          Issue Type: Improvement
            Reporter: Namit Jain


Consider the query like:

select count(*) FROM
        ( select idOne, idTwo, value FROM
              bigTable                                       
              JOIN                                                                
              smallTableOne on (bigTable.idOne = smallTableOne.idOne)                                                   
          ) firstjoin                                                             
            JOIN                                                                  
            smallTableTwo on (firstjoin.idTwo = smallTableTwo.idTwo);


where smallTableOne and smallTableTwo are smaller than hive.auto.convert.join.noconditionaltask.size and
hive.auto.convert.join.noconditionaltask is set to true.

The joins are collapsed into mapjoins, and it leads to a map-only job
(for the map-joins) followed by a map-reduce job (for the group by).
Ideally, the map-only job should be merged with the following map-reduce job.

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