Lateral View optimizations
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Key: HIVE-960
URL: https://issues.apache.org/jira/browse/HIVE-960
Project: Hadoop Hive
Issue Type: New Feature
Components: Query Processor
Reporter: Namit Jain
Assignee: Paul Yang
Had a offline discussion with Paul yesterday.
This is a followup on https://issues.apache.org/jira/browse/HIVE-935
Say, the query is
select .. from T LATERAL VIEW explode(c2_list) as c2 LATERAL VIEW
explode(c3_list) as c3
If we follow the suggestion from
https://issues.apache.org/jira/browse/HIVE-935,
(Lateral View Join operator will always have 2 inputs - the inputs will not be
merged like join),
the explode operator for c3_list will be called once for each input on c2,
which can be expensive.
Instead, if we merge the inputs and let LATERAL VIEW have 3 inputs, we will be
invoking explode
operator for c3_list once for each row.
So, merging should be performed when the right side lateral views are not
referencing anything from the
left side lateral views.
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