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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