[GitHub] [druid] suneet-s commented on a change in pull request #10685: Subtotal queries give incorrect results if query has a limit spec

[GitBox <gi...@apache.org>]

suneet-s commented on a change in pull request #10685:
URL: https://github.com/apache/druid/pull/10685#discussion_r551655397



##########
File path: processing/src/main/java/org/apache/druid/query/groupby/epinephelinae/ByteBufferMinMaxOffsetHeap.java
##########
@@ -59,6 +60,35 @@ public ByteBufferMinMaxOffsetHeap(
     this.heapIndexUpdater = heapIndexUpdater;
   }
 
+  public ByteBufferMinMaxOffsetHeap copy()
+  {
+    LimitedBufferHashGrouper.BufferGrouperOffsetHeapIndexUpdater updater =
+        Optional
+            .ofNullable(heapIndexUpdater)
+            .map(LimitedBufferHashGrouper.BufferGrouperOffsetHeapIndexUpdater::copy)
+            .orElse(null);
+
+    // deep copy buf
+    ByteBuffer buffer = ByteBuffer.allocateDirect(buf.capacity());
+
+    int bufPosition = buf.position();
+    int bufLimit = buf.limit();
+    buf.rewind();
+
+    buffer.put(buf);
+    buffer.position(bufPosition);
+    buffer.limit(bufLimit);
+
+    buf.position(bufPosition);
+    buf.limit(bufLimit);

Review comment:
       nit: It seems like this should be moved in to a separate function since it's used in 2 places. I tried a little googling, and didn't find any libraries that implement deep copying of ByteBuffers which I thought was surprising.
   
   Looking at an implementation I found in http://www.java2s.com/example/java/java.nio/performs-a-deep-copy-on-a-byte-buffer.html, it looks like this implementation does not copy the order of the original ByteBuffer. I can't tell if this is important or not. What do you think?




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