Namit Jain created HIVE-3952:
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Summary: merge map-job followed by map-reduce job
Key: HIVE-3952
URL: https://issues.apache.org/jira/browse/HIVE-3952
Project: Hive
Issue Type: Improvement
Reporter: Namit Jain
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.
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