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

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attilapiros 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_r257186965
 
 

 ##########
 File path: common/network-common/src/main/java/org/apache/spark/network/util/TransportFrameDecoder.java
 ##########
 @@ -123,30 +140,54 @@ private long decodeFrameSize() {
 
   private ByteBuf decodeNext() {
     long frameSize = decodeFrameSize();
-    if (frameSize == UNKNOWN_FRAME_SIZE || totalSize < frameSize) {
+    if (frameSize == UNKNOWN_FRAME_SIZE) {
       return null;
     }
 
-    // Reset size for next frame.
-    nextFrameSize = UNKNOWN_FRAME_SIZE;
-
-    Preconditions.checkArgument(frameSize < MAX_FRAME_SIZE, "Too large frame: %s", frameSize);
-    Preconditions.checkArgument(frameSize > 0, "Frame length should be positive: %s", frameSize);
+    if (frameBuf == null) {
+      Preconditions.checkArgument(frameSize < MAX_FRAME_SIZE,
+          "Too large frame: %s", frameSize);
+      Preconditions.checkArgument(frameSize > 0,
+          "Frame length should be positive: %s", frameSize);
+      frameRemainingBytes = (int) frameSize;
 
-    // If the first buffer holds the entire frame, return it.
-    int remaining = (int) frameSize;
-    if (buffers.getFirst().readableBytes() >= remaining) {
-      return nextBufferForFrame(remaining);
+      // If buffers is empty, then return immediately for more input data.
+      if (buffers.isEmpty()) {
+        return null;
+      }
+      // Otherwise, if the first buffer holds the entire frame, we attempt to
+      // build frame with it and return.
+      if (buffers.getFirst().readableBytes() >= frameRemainingBytes) {
+        // Reset buf and size for next frame.
+        frameBuf = null;
+        nextFrameSize = UNKNOWN_FRAME_SIZE;
+        return nextBufferForFrame(frameRemainingBytes);
+      }
+      // Other cases, create a composite buffer to manage all the buffers.
+      frameBuf = buffers.getFirst().alloc().compositeBuffer(Integer.MAX_VALUE);
     }
 
-    // Otherwise, create a composite buffer.
-    CompositeByteBuf frame = buffers.getFirst().alloc().compositeBuffer(Integer.MAX_VALUE);
-    while (remaining > 0) {
-      ByteBuf next = nextBufferForFrame(remaining);
-      remaining -= next.readableBytes();
-      frame.addComponent(next).writerIndex(frame.writerIndex() + next.readableBytes());
+    while (frameRemainingBytes > 0 && !buffers.isEmpty()) {
+      ByteBuf next = nextBufferForFrame(frameRemainingBytes);
+      frameRemainingBytes -= next.readableBytes();
+      frameBuf.addComponent(true, next);
     }
-    assert remaining == 0;
+    // If the delta size of frameBuf exceeds the threshold, then we do consolidation
+    // to reduce memory consumption.
+    if (frameBuf.capacity() - consolidatedFrameBufSize > consolidateThreshold) {
+      int newNumComponents = frameBuf.numComponents() - consolidatedNumComponents;
+      frameBuf.consolidate(consolidatedNumComponents, newNumComponents);
+      consolidatedFrameBufSize = frameBuf.capacity();
+      consolidatedNumComponents = frameBuf.numComponents();
+    }
+    if (frameRemainingBytes > 0) {
+      return null;
+    }
+
+    // Reset buf and size for next frame.
+    ByteBuf frame = frameBuf;
+    frameBuf = null;
+    nextFrameSize = UNKNOWN_FRAME_SIZE;
 
 Review comment:
   You have to reset `consolidatedFrameBufSize` and `consolidatedNumComponents` back to 0 for the next frame buffer. 
   
   Otherwise after a very huge frame all the smaller but still quite huge frames are not consolidated at all.
   And when consolidation starts as a frame which bigger then the maximum up to this then only the components are consolidated which are after the previous maximum.  
    
   

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