[GitHub] rlodge commented on a change in pull request #23716: [SPARK-26734] [STREAMING] Fix StackOverflowError with large block queue

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rlodge commented on a change in pull request #23716: [SPARK-26734] [STREAMING] Fix StackOverflowError with large block queue
URL: https://github.com/apache/spark/pull/23716#discussion_r252897763
 
 

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 File path: streaming/src/main/scala/org/apache/spark/streaming/scheduler/ReceivedBlockTracker.scala
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 @@ -112,7 +112,7 @@ private[streaming] class ReceivedBlockTracker(
   def allocateBlocksToBatch(batchTime: Time): Unit = synchronized {
     if (lastAllocatedBatchTime == null || batchTime > lastAllocatedBatchTime) {
       val streamIdToBlocks = streamIds.map { streamId =>
-        (streamId, getReceivedBlockQueue(streamId).clone())
+        (streamId, getReceivedBlockQueue(streamId).clone().dequeueAll(x => true))
 
 Review comment:
   Sure, I could do:
   
   `mutable.ArrayBuffer.empty[ReceivedBlockInfo] ++= getReceivedBlockQueue(streamId).clone()`
   
   which ensures that we know exactly the sequence type being serialized; would you prefer I did that?
   
   https://issues.apache.org/jira/browse/SPARK-23991 caused it in the sense that it moved from using dequeueAll to just serializing a clone of the queue, and the queue just doesn't serialize correctly after some number of entries (a scala bug, IMO).  You could say it "uncovered" a scala bug that was sitting there, but prior to that checking the code wouldn't error with large numbers of entries because dequeueAll constructs an ArrayBuffer and that's what was being serialized.

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