[GLUTEN-8629][VL] Add RDDScanExec support to Velox backend

backends-velox/src/main/scala/org/apache/gluten/backendsapi/velox/VeloxSparkPlanExecApi.scala

@@ -1205,6 +1205,11 @@ class VeloxSparkPlanExecApi extends SparkPlanExecApi with Logging {
   override def genColumnarRangeExec(rangeExec: RangeExec): ColumnarRangeBaseExec =
     ColumnarRangeExec(rangeExec.range)
 
+  override def isSupportRDDScanExec(plan: RDDScanExec): Boolean = true
+
+  override def getRDDScanTransform(plan: RDDScanExec): RDDScanTransformer =
+    VeloxRDDScanTransformer.replace(plan)
+
   override def genColumnarTailExec(limit: Int, child: SparkPlan): ColumnarCollectTailBaseExec =
     ColumnarCollectTailExec(limit, child)
 

backends-velox/src/main/scala/org/apache/gluten/execution/VeloxRDDScanTransformer.scala

@@ -0,0 +1,121 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.gluten.execution
+
+import org.apache.gluten.backendsapi.velox.VeloxValidatorApi
+import org.apache.gluten.config.{GlutenConfig, VeloxConfig}
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{Attribute, SortOrder}
+import org.apache.spark.sql.catalyst.plans.physical.Partitioning
+import org.apache.spark.sql.execution.{RDDScanTransformer, SparkPlan}
+import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
+import org.apache.spark.sql.vectorized.ColumnarBatch
+
+/**
+ * Velox-backend implementation of RDDScanTransformer.
+ *
+ * Converts an RDD[InternalRow] into columnar batches using Velox's native row-to-columnar
+ * conversion (same JNI path as RowToVeloxColumnarExec).
+ */
+case class VeloxRDDScanTransformer(
+    outputAttributes: Seq[Attribute],
+    rdd: RDD[InternalRow],
+    name: String,
+    // Row-to-columnar conversion preserves data distribution, so we carry through
+    // the original partitioning. This differs from CH which uses UnknownPartitioning(0)
+    // but is consistent with RowToVeloxColumnarExec's behavior.
+    override val outputPartitioning: Partitioning,
+    override val outputOrdering: Seq[SortOrder]
+) extends RDDScanTransformer(outputAttributes, outputPartitioning, outputOrdering) {
+
+  override def nodeName: String = name
+
+  @transient override lazy val metrics: Map[String, SQLMetric] = Map(
+    "numInputRows" -> SQLMetrics.createMetric(sparkContext, "number of input rows"),
+    "numOutputBatches" -> SQLMetrics.createMetric(sparkContext, "number of output batches"),
+    "convertTime" -> SQLMetrics.createTimingMetric(sparkContext, "time to convert")
+  )
+
+  override protected def doValidateInternal(): ValidationResult = {
+    for (field <- schema.fields) {
+      val reason = VeloxValidatorApi.validateSchema(field.dataType)
+      if (reason.isDefined) {
+        return ValidationResult.failed(reason.get)
+      }
+    }
+    ValidationResult.succeeded
+  }
+
+  override def doExecuteColumnar(): RDD[ColumnarBatch] = {
+    val numInputRows = longMetric("numInputRows")
+    val numOutputBatches = longMetric("numOutputBatches")
+    val convertTime = longMetric("convertTime")
+    val localSchema = this.schema
+    val batchSize = GlutenConfig.get.maxBatchSize
+    val batchBytes = VeloxConfig.get.veloxPreferredBatchBytes
+    rdd.mapPartitions {
+      iter =>
+        if (iter.hasNext) {
+          val first = iter.next()
+          first match {
+            case _: BatchCarrierRow =>
+              // RDD already contains columnar batches wrapped as carrier rows
+              // (e.g., from df.checkpoint() on a Gluten plan). Unwrap directly.
+              (Iterator.single(first) ++ iter).flatMap {
+                row =>
+                  BatchCarrierRow.unwrap(row).map {
+                    batch =>
+                      numOutputBatches += 1
+                      numInputRows += batch.numRows()
+                      batch
+                  }
+              }
+            case _ =>
+              // Standard InternalRow path - convert via native row-to-columnar.
+              RowToVeloxColumnarExec.toColumnarBatchIterator(
+                Iterator.single(first) ++ iter,
+                localSchema,
+                numInputRows,
+                numOutputBatches,
+                convertTime,
+                batchSize,
+                batchBytes)
+          }
+        } else {
+          Iterator.empty
+        }
+    }
+  }
+
+  override protected def withNewChildrenInternal(
+      newChildren: IndexedSeq[SparkPlan]): SparkPlan = {
+    assert(newChildren.isEmpty, "VeloxRDDScanTransformer is a leaf node")
+    copy(outputAttributes, rdd, name, outputPartitioning, outputOrdering)
+  }
+}
+
+object VeloxRDDScanTransformer {
+  def replace(plan: org.apache.spark.sql.execution.RDDScanExec): RDDScanTransformer =
+    VeloxRDDScanTransformer(
+      plan.output,
+      plan.inputRDD,
+      plan.nodeName,
+      plan.outputPartitioning,
+      plan.outputOrdering)
+}

backends-velox/src/test/scala/org/apache/gluten/execution/MiscOperatorSuite.scala

@@ -805,10 +805,10 @@ class MiscOperatorSuite extends VeloxWholeStageTransformerSuite with AdaptiveSpa
     if (isSparkVersionGE("4.1")) {
       assert(plan.find(_.getClass.getSimpleName == "OneRowRelationExec").isDefined)
     } else {
-      assert(plan.find(_.isInstanceOf[RDDScanExec]).isDefined)
+      // RDDScanExec is offloaded to VeloxRDDScanTransformer which handles R2C internally
+      assert(plan.find(_.isInstanceOf[VeloxRDDScanTransformer]).isDefined)
     }
     assert(plan.find(_.isInstanceOf[ProjectExecTransformer]).isDefined)
-    assert(plan.find(_.isInstanceOf[RowToVeloxColumnarExec]).isDefined)
   }
 
   test("equal null safe") {