[jira] [Created] (HIVE-8702) Extra MapTask created but not connected [Spark Branch]

["Xuefu Zhang (JIRA)" <ji...@apache.org>]

Xuefu Zhang created HIVE-8702:
---------------------------------

             Summary: Extra MapTask created but not connected [Spark Branch]
                 Key: HIVE-8702
                 URL: https://issues.apache.org/jira/browse/HIVE-8702
             Project: Hive
          Issue Type: Sub-task
          Components: Spark
            Reporter: Xuefu Zhang


Based on Szehon's observation, there is a strange extra maptask generated but not connected.  Here is the query to demonstrate:

{code}
select * FROM
(SELECT avg(key) as x1, value as x2 FROM src group by value) x
JOIN
(SELECT avg(key) as y1, value as y2 FROM src group by value) y ON (x1 = y1)
JOIN
(SELECT avg(key) as z1, value as z2 FROM src group by value) z ON (x1 = z1);
{code}

We shouldn't generate it in the first place.



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