[GitHub] [spark] cloud-fan commented on a change in pull request #30300: [SPARK-33399][SQL] Normalize output partitioning with respect to aliases to avoid unneeded exchanges

[GitBox <gi...@apache.org>]

cloud-fan commented on a change in pull request #30300:
URL: https://github.com/apache/spark/pull/30300#discussion_r521354211



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/AliasAwareOutputExpression.scala
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@@ -25,20 +25,14 @@ import org.apache.spark.sql.catalyst.plans.physical.{HashPartitioning, Partition
 trait AliasAwareOutputExpression extends UnaryExecNode {
   protected def outputExpressions: Seq[NamedExpression]
 
-  protected def hasAlias: Boolean = outputExpressions.collectFirst { case _: Alias => }.isDefined
+  private lazy val aliasMap = AttributeMap(outputExpressions.collect {
+    case a @ Alias(child: AttributeReference, _) => (child, a.toAttribute)
+  })
 
-  protected def replaceAliases(exprs: Seq[Expression]): Seq[Expression] = {
-    exprs.map {
-      case a: AttributeReference => replaceAlias(a).getOrElse(a)
-      case other => other
-    }
-  }
+  protected def hasAlias: Boolean = aliasMap.nonEmpty
 
   protected def replaceAlias(attr: AttributeReference): Option[Attribute] = {
-    outputExpressions.collectFirst {
-      case a @ Alias(child: AttributeReference, _) if child.semanticEquals(attr) =>
-        a.toAttribute
-    }
+    aliasMap.get(attr)

Review comment:
       do we still need this `replaceAlias` method? It's a very short method.




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