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From "Yin Huai (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-4952) When hive.join.emit.interval is small, queries optimized by Correlation Optimizer may generate wrong results
Date Mon, 29 Jul 2013 22:31:49 GMT
Yin Huai created HIVE-4952:
------------------------------

             Summary: When hive.join.emit.interval is small, queries optimized by Correlation
Optimizer may generate wrong results
                 Key: HIVE-4952
                 URL: https://issues.apache.org/jira/browse/HIVE-4952
             Project: Hive
          Issue Type: Bug
    Affects Versions: 0.12.0
            Reporter: Yin Huai
            Assignee: Yin Huai


If we have a query like this ...
{code:sql}
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;
{\code}

After Correlation Optimizer, the operator tree in the reducer will be 
{code}
     JOIN2
       |
       |
      MUX
     /   \
    /     \
   GBY     |
    |      |
  JOIN1    |
    \     /
     \   /
     DEMUX
{\code}
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.

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