[GitHub] viirya commented on a change in pull request #23740: [SPARK-26837][SQL] Pruning nested fields from object serializers

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viirya commented on a change in pull request #23740: [SPARK-26837][SQL] Pruning nested fields from object serializers
URL: https://github.com/apache/spark/pull/23740#discussion_r254532012
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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 @@ -561,10 +561,31 @@ object ColumnPruning extends Rule[LogicalPlan] {
     case d @ DeserializeToObject(_, _, child) if !child.outputSet.subsetOf(d.references) =>
       d.copy(child = prunedChild(child, d.references))
 
-    case p @ Project(_, s: SerializeFromObject) if p.references != s.outputSet =>
+    case p @ Project(_, s: SerializeFromObject) =>
+      // Prunes individual serializer if it is not used at all by above projection.
       val usedRefs = p.references
       val prunedSerializer = s.serializer.filter(usedRefs.contains)
-      p.copy(child = SerializeFromObject(prunedSerializer, s.child))
+
+      val fields = SchemaPruning.identifyRootFields(p.projectList, Seq.empty)
+
+      if (SQLConf.get.serializerNestedSchemaPruningEnabled && fields.nonEmpty) {
+        // Prunes nested fields in serialzers.
+        val prunedSchema = SchemaPruning.pruneDataSchema(
 
 Review comment:
   I think we can skip pruning if `prunedSchema` is as same as original one. But I keep it simpler now for review. Can update it later.

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