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https://issues.apache.org/jira/browse/SPARK-59413?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-59413:
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Labels: pull-request-available (was: )
> Treat the Collate passthrough as cheap in CollapseProject.isCheap
> -----------------------------------------------------------------
>
> Key: SPARK-59413
> URL: https://issues.apache.org/jira/browse/SPARK-59413
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 4.1.0
> Reporter: David Mollitor
> Priority: Minor
> Labels: pull-request-available
>
> h2. Summary
> {{CollapseProject.isCheap(e: Expression)}} decides whether an expression is
> cheap enough to duplicate/inline. It currently returns true for {{Attribute}}
> / {{OuterReference}} /
> {{BoundReference}}, foldable expressions, some {{PythonUDF}}s, and {{Alias}}
> / {{ExtractValue}} over cheap children -- but it does not recognize the
> {{Collate}} expression.
> {{Collate}} (the SQL {{collate(expr, 'COLLATION')}} function / {{expr COLLATE
> COLLATION}} syntax) is a pure
> [pass-through|https://github.com/apache/spark/blob/0cfb8bfca7d87769b618b43010da8f50c0b62218/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collationExpressions.scala#L69-L74]:
> its {{eval}} delegates directly to the child ({{child.eval(row)}}), its
> codegen delegates to the child ({{child.genCode(ctx)}}), and it never
> evaluates its collation argument. It performs no per-row work -- it only
> re-tags the collation carried in the result _type_. It is deterministic and,
> at runtime, exactly as cheap as the child it wraps.
> Because {{isCheap}} does not know this, {{Collate(cheapChild)}} is treated as
> non-cheap. That needlessly blocks safe duplication/inlining of collated
> columns across every {{isCheap}}-gated rule (CollapseProject inlining, the
> multi-LIKE {{LikeSimplification}} rules, the {{FilterExec}} CSE gate,
> {{RewriteWithExpression}}).
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