[GitHub] [spark] taroplus commented on a change in pull request #33981: [SPARK-36733][SQL] Fix a perf issue in SchemaPruning when a struct has many fields

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taroplus commented on a change in pull request #33981:
URL: https://github.com/apache/spark/pull/33981#discussion_r707887231



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/SchemaPruning.scala
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@@ -65,16 +67,19 @@ object SchemaPruning extends SQLConfHelper {
           sortLeftFieldsByRight(leftValueType, rightValueType),
           containsNull)
       case (leftStruct: StructType, rightStruct: StructType) =>
-        val resolver = conf.resolver
-        val filteredRightFieldNames = rightStruct.fieldNames
-          .filter(name => leftStruct.fieldNames.exists(resolver(_, name)))
-        val sortedLeftFields = filteredRightFieldNames.map { fieldName =>
-          val resolvedLeftStruct = leftStruct.find(p => resolver(p.name, fieldName)).get
-          val leftFieldType = resolvedLeftStruct.dataType
-          val rightFieldType = rightStruct(fieldName).dataType
-          val sortedLeftFieldType = sortLeftFieldsByRight(leftFieldType, rightFieldType)
-          StructField(fieldName, sortedLeftFieldType, nullable = resolvedLeftStruct.nullable,
-            metadata = resolvedLeftStruct.metadata)
+        val leftStructTreeMap =

Review comment:
       based on my use-cases, often times left and right are the same thing, can we have a condition like
   ```
   case (_, _) if left == right => left
   ```
   i'm not sure if we need to recreate the whole thing for those situations




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