HyukjinKwon commented on code in PR #38468:
URL: https://github.com/apache/spark/pull/38468#discussion_r1013556642


##########
sql/core/src/main/scala/org/apache/spark/sql/execution/arrow/ArrowConverters.scala:
##########
@@ -128,6 +128,65 @@ private[sql] object ArrowConverters extends Logging {
     }
   }
 
+  private[sql] def toArrowBatchIterator(
+      rowIter: Iterator[InternalRow],
+      schema: StructType,
+      maxRecordsPerBatch: Int,
+      timeZoneId: String,
+      context: TaskContext): Iterator[(Array[Byte], Long, Long)] = {
+    val arrowSchema = ArrowUtils.toArrowSchema(schema, timeZoneId)
+    val allocator = ArrowUtils.rootAllocator.newChildAllocator(
+      "toArrowBatchIterator", 0, Long.MaxValue)
+
+    val root = VectorSchemaRoot.create(arrowSchema, allocator)
+    val unloader = new VectorUnloader(root)
+    val arrowWriter = ArrowWriter.create(root)
+
+    if (context != null) { // for test at driver
+      context.addTaskCompletionListener[Unit] { _ =>
+        root.close()
+        allocator.close()
+      }
+    }
+
+    new Iterator[(Array[Byte], Long, Long)] {
+
+      override def hasNext: Boolean = rowIter.hasNext || {
+        root.close()
+        allocator.close()
+        false
+      }
+
+      override def next(): (Array[Byte], Long, Long) = {
+        val out = new ByteArrayOutputStream()
+        val writeChannel = new WriteChannel(Channels.newChannel(out))
+
+        var rowCount = 0L
+        var estimatedSize = 0L
+        Utils.tryWithSafeFinally {
+          while (rowIter.hasNext && (maxRecordsPerBatch <= 0 || rowCount < 
maxRecordsPerBatch)) {
+            val row = rowIter.next()
+            arrowWriter.write(row)
+            rowCount += 1
+            estimatedSize += SizeEstimator.estimate(row)
+          }
+          arrowWriter.finish()
+          val batch = unloader.getRecordBatch()
+
+          MessageSerializer.serialize(writeChannel, arrowSchema)

Review Comment:
   The problem is that we carry Arrow record batch within each protobuf 
message. So, schema of each recordbatch has to be sent in order to read each 
protobuf message.



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