hvanhovell commented on code in PR #40610:
URL: https://github.com/apache/spark/pull/40610#discussion_r1153980266


##########
connector/connect/client/jvm/src/main/scala/org/apache/spark/sql/connect/client/SparkResult.scala:
##########
@@ -134,24 +134,41 @@ private[sql] class SparkResult[T](
   /**
    * Returns an iterator over the contents of the result.
    */
-  def iterator: java.util.Iterator[T] with AutoCloseable = {
+  def iterator: java.util.Iterator[T] with AutoCloseable =
+    buildIterator(destructive = false)
+
+  /**
+   * Returns an destructive iterator over the contents of the result.
+   */
+  def destructiveIterator: java.util.Iterator[T] with AutoCloseable =
+    buildIterator(destructive = true)
+
+  private def buildIterator(destructive: Boolean): java.util.Iterator[T] with 
AutoCloseable = {
     new java.util.Iterator[T] with AutoCloseable {
-      private[this] var batchIndex: Int = -1
       private[this] var iterator: java.util.Iterator[InternalRow] = 
Collections.emptyIterator()
       private[this] var deserializer: Deserializer[T] = _
+      private[this] var currentBatch: ColumnarBatch = _
+      private[this] val _destructive: Boolean = destructive
+
       override def hasNext: Boolean = {
         if (iterator.hasNext) {
           return true
         }
-        val nextBatchIndex = batchIndex + 1
+        val batchIndex = batches.indexOf(currentBatch)

Review Comment:
    I have been looking at this a for a bit now. I am not sure if I like it. 
There are two issues:
   - In destructive mode you know the location of the current batch. It should 
be at index = 0. In non destructive mode the index should be `batchIndex`. We 
are not doing anything with that information.
   - The removal can be pretty expensive since we are removing from the head.
   
   I am wondering if we can use a better suited data structure here. You could 
use a map, since that will give you cheap removals, and fairly fast lookups. 
Alternatively we could implement something a-kin to a linkedlist (I don't think 
you can use a stock linked list since those don't like updates during 
iteration).



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