L. C. Hsieh created SPARK-35439:
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Summary: Use LinkedHashMap as the map of equivalent expressions to
preserve insertion order
Key: SPARK-35439
URL: https://issues.apache.org/jira/browse/SPARK-35439
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 3.1.1, 3.0.2, 3.2.0
Reporter: L. C. Hsieh
Assignee: L. C. Hsieh
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.
Although we add expressions recursively into the map with depth-first approach,
when we retrieve the map values, it is not guaranteed that the order is
preserved. We should use LinkedHashMap for this usage.
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