hvanhovell commented on code in PR #38468:
URL: https://github.com/apache/spark/pull/38468#discussion_r1019032161


##########
connector/connect/src/main/scala/org/apache/spark/sql/connect/service/SparkConnectStreamHandler.scala:
##########
@@ -114,10 +123,97 @@ class SparkConnectStreamHandler(responseObserver: 
StreamObserver[Response]) exte
       responseObserver.onNext(response.build())
     }
 
-    responseObserver.onNext(sendMetricsToResponse(clientId, rows))
+    responseObserver.onNext(sendMetricsToResponse(clientId, dataframe))
     responseObserver.onCompleted()
   }
 
+  def processRowsAsArrowBatches(clientId: String, dataframe: DataFrame): Unit 
= {
+    val spark = dataframe.sparkSession
+    val schema = dataframe.schema
+    // TODO: control the batch size instead of max records
+    val maxRecordsPerBatch = spark.sessionState.conf.arrowMaxRecordsPerBatch
+    val timeZoneId = spark.sessionState.conf.sessionLocalTimeZone
+
+    SQLExecution.withNewExecutionId(dataframe.queryExecution, 
Some("collectArrow")) {
+      val rows = dataframe.queryExecution.executedPlan.execute()
+      val numPartitions = rows.getNumPartitions
+      var numSent = 0
+
+      if (numPartitions > 0) {
+        type Batch = (Array[Byte], Long, Long)
+
+        val batches = rows.mapPartitionsInternal { iter =>
+          ArrowConverters
+            .toArrowBatchIterator(iter, schema, maxRecordsPerBatch, timeZoneId)
+        }
+
+        val signal = new Object
+        val partitions = Array.fill[Array[Batch]](numPartitions)(null)
+
+        val processPartition = (iter: Iterator[Batch]) => iter.toArray
+
+        val resultHandler = (partitionId: Int, partition: Array[Batch]) => {
+          signal.synchronized {
+            partitions(partitionId) = partition
+            signal.notify()
+          }
+          val i = 0 // Unit
+        }
+
+        spark.sparkContext.runJob(batches, processPartition, resultHandler)
+
+        var currentPartitionId = 0
+        while (currentPartitionId < numPartitions) {
+          val partition = signal.synchronized {
+            while (partitions(currentPartitionId) == null) {
+              signal.wait()

Review Comment:
   That is an optimization we can go for after merging this. My only problem 
with that is that it might scare users, because collecting a dataframe multiple 
times might have a results that look differently.



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