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https://issues.apache.org/jira/browse/CALCITE-3829?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ruben Q L updated CALCITE-3829:
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Fix Version/s: 1.23.0
> MergeJoinEnumerator should not use inputs enumerators until it is really
> required
> ---------------------------------------------------------------------------------
>
> Key: CALCITE-3829
> URL: https://issues.apache.org/jira/browse/CALCITE-3829
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.21.0
> Reporter: Ruben Q L
> Assignee: Ruben Q L
> Priority: Minor
> Labels: pull-request-available
> Fix For: 1.23.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> {{EnumerableDefaults#MergeJoinEnumerator}} provides an {{Enumerator}} that
> performs a merge join between two sorted inputs. This sort operation can be
> potentially very expensive, so we should skip it if possible. Right now,
> merge join inputs' enumerators are created when {{MergeJoinEnumerator}} is
> constructed; however, there are some cases where we can skip the enumerator
> creation of one input: if the outer (i.e. left) enumerator returns no
> results, there is no need to access (and sort) the inner (i.e. right)
> enumerator. For this reason, we should delay the inner enumerator creation
> until the moment we are sure it is really required: when the first element of
> the outer enumerator is fetched. This strategy is already in place in other
> join algorithms in {{EnumerableDefaults}} (e.g. {{nestedLoopJoinOptimized}},
> {{semiEquiJoin}}), and it will be quite easy to apply on
> {{MergeJoinEnumerator}}.
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