[jira] [Created] (TAJO-593) outer groupby and groupby in derived table causes only one shuffle output number

["Hyunsik Choi (JIRA)" <ji...@apache.org>]

Hyunsik Choi created TAJO-593:
---------------------------------

             Summary: outer groupby and groupby in derived table causes only one shuffle output number
                 Key: TAJO-593
                 URL: https://issues.apache.org/jira/browse/TAJO-593
             Project: Tajo
          Issue Type: Bug
          Components: distributed query plan
            Reporter: Hyunsik Choi
            Assignee: Hyunsik Choi
             Fix For: 0.8-incubating


See the following query case:

{code:sql}
select count(*) from (select l_orderkey, l_partkey, count(*) from lineitem group by l_orderkey, l_partkey) t1;
{code}

In this case, SubQuery::calculateShuffleOutputNum() are used two times for choosing the number of shuffle outputs. At that time, SubQuery::calculateShuffleOutputNum() method finds GroupByNode to know the number of grouping keys. Here is one bug. SubQuery::calculateShuffleOutputNum() always the topmost GroupByNode. In most cases, it work well. But, outer groupby and groupby in derived table can cause the problem. In this case, we must use the most bottom groupby node. Actually, it is always the correct way.

This patch fixes SubQuery::calculateShuffleOutputNum() to use the most bottom groupby node.



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