Ruben Quesada Lopez created CALCITE-2909:
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Summary: Optimize Enumerable SemiJoin with a lazy evaluation of
innerLookup
Key: CALCITE-2909
URL: https://issues.apache.org/jira/browse/CALCITE-2909
Project: Calcite
Issue Type: Improvement
Affects Versions: 1.18.0
Reporter: Ruben Quesada Lopez
Assignee: Ruben Quesada Lopez
The implementation of semiJoin in EnumerableDefaults.java is based on two
elements: an outer enumerator and an inner lookup. The method "returns elements
of outer for which there is a member of inner with a matching key".
In order to achieve that, the innerLookup is always eagerly computed, even
though in some cases it might be not necessary at all: when the outer
enumerator returns no element there is no need for the innerLookup. In a worst
case scenario, a time-consuming innerLookup computation combined with an empty
outer enumerator will lead to an inefficient execution, which could have been
easily avoided.
In order to improve that, it is proposed to delay the computation of the
innerLookup until the moment when we are sure that it will be really needed,
i.e. when the first outer enumerator item is processed.
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