[GitHub] vanzin commented on a change in pull request #23602: [SPARK-26674][CORE]Consolidate CompositeByteBuf when reading large frame

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vanzin commented on a change in pull request #23602: [SPARK-26674][CORE]Consolidate CompositeByteBuf when reading large frame
URL: https://github.com/apache/spark/pull/23602#discussion_r253687077
 
 

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 File path: common/network-common/src/main/java/org/apache/spark/network/util/TransportFrameDecoder.java
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 @@ -141,10 +153,20 @@ private ByteBuf decodeNext() {
 
     // Otherwise, create a composite buffer.
     CompositeByteBuf frame = buffers.getFirst().alloc().compositeBuffer(Integer.MAX_VALUE);
+    long lastConsolidatedCapacity = 0L;
     while (remaining > 0) {
       ByteBuf next = nextBufferForFrame(remaining);
       remaining -= next.readableBytes();
       frame.addComponent(next).writerIndex(frame.writerIndex() + next.readableBytes());
+      if (frame.capacity() - lastConsolidatedCapacity >= consolidateBufsThreshold) {
 
 Review comment:
   If your goal is really to save memory, shouldn't you be doing the consolidation earlier, before you have all the data for the frame?
   
   Otherwise, because of the return in L139, you basically are wasting this memory anyway until the whole frame arrives.

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