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new 81dce78385 fix off by one error for slice accounting (#10406)
81dce78385 is described below
commit 81dce783858cd79eab56eca12dc99bc40b7bf019
Author: RIchard Baah <[email protected]>
AuthorDate: Wed Jul 22 21:09:56 2026 -0400
fix off by one error for slice accounting (#10406)
# Which issue does this PR close?
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enhancements and this helps us generate change logs for our releases.
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- Closes #10385.
- works towards closing #10383
# Rationale for this change
`get_slice_memory_size` is used to estimate how much memory a slice of
an ArrayData actually occupies. For variable-width types (Utf8, Binary,
List, etc.), the offset buffer stores len+1 boundaries, one per element
plus a final entry marking the end of the last element. The old code
calculated `len * byte_width`, missing that final boundary and
consistently under-reporting the size of any array using an offset
buffer.
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in the issue then this section is not needed.
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# What changes are included in this PR?
the FixedWidth buffer size is now calculated as (len + 1) * byte_width
instead of len * byte_width.
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is sometimes worth providing a summary of the individual changes in this
PR.
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# Are these changes tested?
Yes I added two test for string arrays and binary arrays. existing test
still pass
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# Are there any user-facing changes?
users will have more accurate memory accounting
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---
arrow-data/src/data.rs | 52 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 51 insertions(+), 1 deletion(-)
diff --git a/arrow-data/src/data.rs b/arrow-data/src/data.rs
index 0e0ef9e9a4..8a037bc0f5 100644
--- a/arrow-data/src/data.rs
+++ b/arrow-data/src/data.rs
@@ -530,7 +530,19 @@ impl ArrayData {
for spec in layout.buffers.iter() {
match spec {
BufferSpec::FixedWidth { byte_width, .. } => {
- let buffer_size =
self.len.checked_mul(*byte_width).ok_or_else(|| {
+ // Offset buffers contain len+1 elements: one boundary per
element
+ // plus a final boundary marking the end of the last
element.
+ let len = match self.data_type {
+ DataType::Utf8
+ | DataType::LargeUtf8
+ | DataType::Binary
+ | DataType::LargeBinary
+ | DataType::List(_)
+ | DataType::LargeList(_)
+ | DataType::Map(_, _) => self.len + 1,
+ _ => self.len,
+ };
+ let buffer_size =
len.checked_mul(*byte_width).ok_or_else(|| {
ArrowError::ComputeError(
"Integer overflow computing buffer
size".to_string(),
)
@@ -2616,6 +2628,44 @@ mod tests {
assert!(!string_data_slice.ptr_eq(&string_data))
}
+ #[test]
+ fn test_slice_memory_size_utf8_offset_buffer_len_plus_one() {
+ // 2-element array ["hello", "world"]: array len = 2, 10 bytes
+ let data_buffer = Buffer::from_slice_ref("helloworld".as_bytes());
+ // offsets need array_len+1 entries to mark the end of every string:
+ // [0, 5, 10] -> 3 i32s = 12 bytes
+ let offsets_buffer = Buffer::from_slice_ref([0_i32, 5_i32, 10_i32]);
+ let array = ArrayData::try_new(
+ DataType::Utf8,
+ 2,
+ None,
+ 0,
+ vec![offsets_buffer, data_buffer],
+ vec![],
+ )
+ .unwrap();
+ assert_eq!(array.get_slice_memory_size().unwrap(), 22); // 12 + 10
+ }
+
+ #[test]
+ fn test_slice_memory_size_binary_offset_buffer_len_plus_one() {
+ // 2-element array: array len = 2, not 3
+ // values: 5 bytes
+ let data_buffer = Buffer::from_slice_ref([0u8, 1, 2, 3, 4]);
+ // offsets need array_len+1 entries to mark the end of every element:
+ let offsets_buffer = Buffer::from_slice_ref([0_i32, 2_i32, 5_i32]);
+ let array = ArrayData::try_new(
+ DataType::Binary,
+ 2,
+ None,
+ 0,
+ vec![offsets_buffer, data_buffer],
+ vec![],
+ )
+ .unwrap();
+ assert_eq!(array.get_slice_memory_size().unwrap(), 17); // 12 + 5
+ }
+
#[test]
fn test_slice_memory_size() {
let mut bit_v: [u8; 2] = [0; 2];
