scampi commented on a change in pull request #6402:
URL: https://github.com/apache/arrow/pull/6402#discussion_r439780145
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File path:
java/vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthVector.java
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@@ -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:
> If the testSplitAndTransfer tests were run with two child buffer
allocators I think they would fail.
@rymurr there was indeed a problem in that case where the sliced data was
not transferred to the target allocator. See
681327e22f6dbda71b78e408b9fee6a8af0040b0 for a test about that.
> A clearer/more complete optimization would probably to simply read the
initial starting offset at the index that we're slicing from and if that is
zero, don't do the allocate/copy
@jacques-n I have extended the condition to include also that case of
empties/nulls. See 2e13c5239137e54b0cd128240e6a3d0895c0c36f
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