[HIVE-4952] When hive.join.emit.interval is small, queries optimized by Correlation Optimizer may generate wrong results

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.12.0
• Fix Version/s: 0.12.0
• Assignee: Yin Huai
• Reporter: Yin Huai
• Created: 29/Jul/13 22:30
• Updated: 15/Oct/13 23:29
• Resolved: 02/Aug/13 04:53

Description

If we have a query like this ...

SELECT xx.key, xx.cnt, yy.key
FROM
(SELECT x.key as key, count(1) as cnt FROM src1 x JOIN src1 y ON (x.key = y.key) group by x.key) xx
JOIN src yy
ON xx.key=yy.key;

After Correlation Optimizer, the operator tree in the reducer will be

     JOIN2
       |
       |
      MUX
     /   \
    /     \
   GBY     |
    |      |
  JOIN1    |
    \     /
     \   /
     DEMUX

For JOIN2, the right table will arrive at this operator first. If hive.join.emit.interval is small, e.g. 1, JOIN2 will output the results even it has not got any row from the left table. The logic related hive.join.emit.interval in JoinOperator assumes that inputs will be ordered by the tag. But, if a query has been optimized by Correlation Optimizer, this assumption may not hold for those JoinOperators inside the reducer.