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https://issues.apache.org/jira/browse/SPARK-35439?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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L. C. Hsieh updated SPARK-35439:
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Affects Version/s: (was: 3.1.1)
(was: 3.0.2)
> Children subexpr should come first than parent subexpr in subexpression
> elimination
> -----------------------------------------------------------------------------------
>
> Key: SPARK-35439
> URL: https://issues.apache.org/jira/browse/SPARK-35439
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: L. C. Hsieh
> Assignee: Apache Spark
> Priority: Major
>
> EquivalentExpressions maintains a map of equivalent expressions. It is
> HashMap now so the insertion order is not guaranteed to be preserved later.
> Subexpression elimination relies on retrieving subexpressions from the map.
> If there is child-parent relationships among the subexpressions, we want the
> child expressions come first than parent expressions, so we can replace child
> expressions in parent expressions with subexpression evaluation.
> For example, we have two different expressions Add(Literal(1), Literal(2))
> and Add(Literal(3), add).
> Case 1: child subexpr comes first. Replacing HashMap with LinkedHashMap can
> deal with it.
> addExprTree(add)
> addExprTree(Add(Literal(3), add))
> addExprTree(Add(Literal(3), add))
> Case 2: parent subexpr comes first. For this case, we need to sort equivalent
> expressions.
> addExprTree(Add(Literal(3), add)) => We add `Add(Literal(3), add)` into the
> map first, then add `add` into the map
> addExprTree(add)
> addExprTree(Add(Literal(3), add))
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