[HIVE-8702] Extra MapTask created but not connected [Spark Branch]

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Component/s: Spark
• Assignee: Szehon Ho
• Reporter: Xuefu Zhang
• Created: 02/Nov/14 15:53
• Updated: 04/Nov/14 00:21
• Resolved: 04/Nov/14 00:21

Description

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

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);

We shouldn't generate it in the first place.