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GH-1190: Reserve view slots for empty view vector values #1192

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GH-1190: Reserve view slots for empty view vector values #1192

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3 changes: 2 additions & 1 deletion vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthViewVector.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1405,7 +1405,8 @@ public final int getTotalValueLengthUpToIndex(int index) {
}

protected final void handleSafe(int index, int dataLength) {
final long targetCapacity = roundUpToMultipleOf16((long) index * ELEMENT_SIZE + dataLength);
// The view buffer stores one fixed-width view per value; payload bytes are allocated separately.
final long targetCapacity = roundUpToMultipleOf16(((long) index + 1) * ELEMENT_SIZE);

@mbutrovich mbutrovich Jul 8, 2026

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Correct. Reserves the full slot regardless of payload; ((long) index + 1) avoids overflow. roundUpToMultipleOf16 is a no-op here but fine to keep.

if (viewBuffer.capacity() < targetCapacity) {
reallocViewBuffer(targetCapacity);
}
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20 changes: 20 additions & 0 deletions vector/src/test/java/org/apache/arrow/vector/TestVariableWidthViewVector.java
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Expand Up @@ -540,6 +540,26 @@ public void testSizeOfViewBufferElements() {
}
}

@ParameterizedTest
@MethodSource({"vectorCreatorProvider"})
public void testSetSafeEmptyValueAtViewBufferBoundary(

@mbutrovich mbutrovich Jul 8, 2026 •
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Only covers the empty-value path. setNull and fillEmpties/setValueCount reach the same handleSafe(index, 0). Suggest adding tests for those.

setValueCount trailing gap (silent trigger, no empty string written)

@ParameterizedTest
@MethodSource({"vectorCreatorProvider"})
public void testSetValueCountFillsEmptiesAtViewBufferBoundary(
    Function<BufferAllocator, BaseVariableWidthViewVector> vectorCreator) {
  try (final BaseVariableWidthViewVector vector = vectorCreator.apply(allocator)) {
    vector.allocateNew();
    final int valueCapacity = vector.getValueCapacity();
    vector.setSafe(valueCapacity - 1, "x".getBytes(StandardCharsets.UTF_8));
    // Leaves index valueCapacity unset: fillEmpties -> handleSafe(_, 0) on a full buffer.
    vector.setValueCount(valueCapacity + 1);
    assertTrue(vector.getValueCapacity() > valueCapacity);
    assertTrue(vector.isNull(valueCapacity));
  }
}

setNull at the boundary

@ParameterizedTest
@MethodSource({"vectorCreatorProvider"})
public void testSetNullAtViewBufferBoundary(
    Function<BufferAllocator, BaseVariableWidthViewVector> vectorCreator) {
  try (final BaseVariableWidthViewVector vector = vectorCreator.apply(allocator)) {
    vector.allocateNew();
    final int valueCapacity = vector.getValueCapacity();
    for (int i = 0; i <= valueCapacity; i++) {
      vector.setNull(i);
    }
    vector.setValueCount(valueCapacity + 1);
    assertTrue(vector.getValueCapacity() > valueCapacity);
    assertTrue(vector.isNull(valueCapacity));
  }
}

Function<BufferAllocator, BaseVariableWidthViewVector> vectorCreator) {
try (final BaseVariableWidthViewVector vector = vectorCreator.apply(allocator)) {
final byte[] emptyValue = new byte[0];
vector.allocateNew();
final int valueCapacity = vector.getValueCapacity();

for (int i = 0; i <= valueCapacity; i++) {
vector.setSafe(i, emptyValue);
}

vector.setValueCount(valueCapacity + 1);
assertTrue(vector.getValueCapacity() > valueCapacity);
assertEquals(0, vector.getValueLength(valueCapacity));
assertArrayEquals(emptyValue, vector.get(valueCapacity));
}
}

@Test
public void testNullableVarType1() {

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