[GitHub] [arrow] scampi commented on a change in pull request #6402: ARROW-7831: [Java] do not allocate a new offset buffer if the slice starts at 0 since the relative offset pointer would be unchanged

[GitBox]

scampi commented on a change in pull request #6402:
URL: https://github.com/apache/arrow/pull/6402#discussion_r422419677



##########
File path: 
java/vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthVector.java
##########
@@ -740,10 +740,16 @@ private void splitAndTransferOffsetBuffer(int startIndex, 
int length, BaseVariab
     final int start = offsetBuffer.getInt(startIndex * OFFSET_WIDTH);
     final int end = offsetBuffer.getInt((startIndex + length) * OFFSET_WIDTH);
     final int dataLength = end - start;
-    target.allocateOffsetBuffer((length + 1) * OFFSET_WIDTH);
-    for (int i = 0; i < length + 1; i++) {
-      final int relativeSourceOffset = offsetBuffer.getInt((startIndex + i) * 
OFFSET_WIDTH) - start;
-      target.offsetBuffer.setInt(i * OFFSET_WIDTH, relativeSourceOffset);
+
+    if (startIndex == 0) {
+      target.offsetBuffer = offsetBuffer.slice(0, (1 + length) * OFFSET_WIDTH);
+      target.offsetBuffer.getReferenceManager().retain();

Review comment:
       > We should also verify that reference management and accounting is 
intact after this change
   
   @siddharthteotia  I have added a test but this is not checked. Do you have 
some pointers on how I can check this?
   
   > do you want to transfer the buffer here as well?
   
   @emkornfield What do you mean?




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