Details
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Type:
Improvement
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Status: Closed
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Priority:
Major
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: 0.11.0
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Component/s: Query Processor
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Labels:None
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Hadoop Flags:Reviewed
Description
Consider the query like:
select count（*）FROM
( select idOne, idTwo, value FROM
bigTable
JOIN
smallTableOne on (bigTable.idOne = smallTableOne.idOne)
) firstjoin
JOIN
smallTableTwo on (firstjoin.idTwo = smallTableTwo.idTwo);
where smallTableOne and smallTableTwo are smaller than hive.auto.convert.join.noconditionaltask.size and
hive.auto.convert.join.noconditionaltask is set to true.
The joins are collapsed into mapjoins, and it leads to a map-only job
(for the map-joins) followed by a map-reduce job (for the group by).
Ideally, the map-only job should be merged with the following map-reduce job.
