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Optimize Spark hex null handling #23688

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10 changes: 10 additions & 0 deletions datafusion/spark/benches/hex.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -135,11 +135,21 @@ fn criterion_benchmark(c: &mut Criterion) {
run_benchmark(c, "hex_utf8", size, Arc::new(data));
}

for &size in &sizes {
let data = generate_utf8_data(size, 0.0);
run_benchmark(c, "hex_utf8_no_nulls", size, Arc::new(data));
}

for &size in &sizes {
let data = generate_binary_data(size, null_density);
run_benchmark(c, "hex_binary", size, Arc::new(data));
}

for &size in &sizes {
let data = generate_binary_data(size, 0.0);
run_benchmark(c, "hex_binary_no_nulls", size, Arc::new(data));
}

for &size in &sizes {
let data = generate_int64_dict_data(size, null_density);
run_benchmark(c, "hex_int64_dict", size, Arc::new(data));
Expand Down
174 changes: 107 additions & 67 deletions datafusion/spark/src/function/math/hex.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
use std::str::from_utf8_unchecked;
use std::sync::Arc;

use arrow::array::{Array, ArrayRef, NullBufferBuilder, StringArray, StringBuilder};
use arrow::array::{Array, ArrayAccessor, ArrayRef, StringArray, StringBuilder};
use arrow::buffer::{Buffer, OffsetBuffer};
use arrow::datatypes::DataType;
use arrow::{
Expand Down Expand Up @@ -158,21 +158,42 @@ fn hex_int64(num: i64, buffer: &mut [u8; 16]) -> &[u8] {
&buffer[i..]
}

#[inline]
fn append_hex_bytes(
values: &mut Vec<u8>,
bytes: &[u8],
lookup: &[[u8; 2]; 256],
) -> Result<i32, DataFusionError> {
let additional = bytes
.len()
.checked_mul(2)
.ok_or_else(|| exec_datafusion_err!("hex output size overflow"))?;
values.try_reserve(additional).map_err(|e| {
exec_datafusion_err!("failed to reserve {additional} bytes for hex output: {e}")
})?;
for &byte in bytes {
values.extend_from_slice(&lookup[byte as usize]);
}
i32::try_from(values.len())
.map_err(|_| exec_datafusion_err!("hex output exceeds i32 offset range"))
}

/// Generic hex encoding for byte array types
fn hex_encode_bytes<'a, I, T>(
iter: I,
fn hex_encode_bytes<'a, A, T>(
array: &A,
lowercase: bool,
len: usize,
) -> Result<ArrayRef, DataFusionError>
where
I: Iterator<Item = Option<T>>,
T: AsRef<[u8]> + 'a,
A: ArrayAccessor<Item = &'a T>,
T: AsRef<[u8]> + ?Sized + 'a,
{
let lookup = if lowercase {
&HEX_LOOKUP_LOWER
} else {
&HEX_LOOKUP_UPPER
};
let len = array.len();
let nulls = array.nulls().cloned();

// Write hex digits directly into one growing value buffer, tracking offsets
// ourselves. Each input byte becomes exactly two output bytes, so there is
Expand All @@ -181,32 +202,25 @@ where
let mut values: Vec<u8> = Vec::with_capacity(len * 64);
let mut offsets: Vec<i32> = Vec::with_capacity(len + 1);
offsets.push(0);
let mut nulls = NullBufferBuilder::new(len);

for v in iter {
if let Some(b) = v {
let bytes = b.as_ref();
let additional = bytes
.len()
.checked_mul(2)
.ok_or_else(|| exec_datafusion_err!("hex output size overflow"))?;
values.try_reserve(additional).map_err(|e| {
exec_datafusion_err!(
"failed to reserve {additional} bytes for hex output: {e}"
)
})?;
for &byte in bytes {
values.extend_from_slice(&lookup[byte as usize]);
if let Some(ref nulls) = nulls {
for i in 0..len {
if nulls.is_valid(i) {
// SAFETY: `i` is in bounds and the validity buffer marks it valid.
let bytes = unsafe { array.value_unchecked(i) }.as_ref();
offsets.push(append_hex_bytes(&mut values, bytes, lookup)?);
} else {
offsets.push(i32::try_from(values.len()).map_err(|_| {
exec_datafusion_err!("hex output exceeds i32 offset range")
})?);
}
nulls.append_non_null();
} else {
nulls.append_null();
}
offsets.push(
i32::try_from(values.len()).map_err(|_| {
exec_datafusion_err!("hex output exceeds i32 offset range")
})?,
);
} else {
for i in 0..len {
// SAFETY: `i` is in bounds and no null buffer means every value is valid.
let bytes = unsafe { array.value_unchecked(i) }.as_ref();
offsets.push(append_hex_bytes(&mut values, bytes, lookup)?);
}
}

// SAFETY: the value buffer contains only ASCII hex digits (valid UTF-8) and
Expand All @@ -217,7 +231,7 @@ where
StringArray::new_unchecked(
OffsetBuffer::new(offsets.into()),
Buffer::from_vec(values),
nulls.finish(),
nulls,
)
};
Ok(Arc::new(array))
Expand Down Expand Up @@ -276,51 +290,27 @@ pub fn compute_hex(
}
DataType::Utf8 => {
let array = as_string_array(array);
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::Utf8View => {
let array = as_string_view_array(array)?;
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::LargeUtf8 => {
let array = as_largestring_array(array);
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::Binary => {
let array = as_binary_array(array)?;
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::LargeBinary => {
let array = as_large_binary_array(array)?;
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::FixedSizeBinary(_) => {
let array = as_fixed_size_binary_array(array)?;
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
Ok(ColumnarValue::Array(hex_encode_bytes(&array, lowercase)?))
}
DataType::Dictionary(key_type, _) => {
if **key_type != DataType::Int32 {
Expand All @@ -340,27 +330,27 @@ pub fn compute_hex(
}
DataType::Utf8 => {
let arr = as_string_array(dict_values);
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
DataType::LargeUtf8 => {
let arr = as_largestring_array(dict_values);
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
DataType::Utf8View => {
let arr = as_string_view_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
DataType::Binary => {

@kosiew kosiew Jul 27, 2026

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Could we add a small regression test for a dictionary-backed Binary or LargeBinary array where dict.values() itself contains a null, rather than only testing null dictionary keys? The new byte-array path preserves the values array NullBuffer directly. We already cover this shape for Int64 in test_dict_values_null, so matching binary coverage would help pin down this updated path. This is optional and does not need to block the PR.

let arr = as_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
DataType::LargeBinary => {
let arr = as_large_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
DataType::FixedSizeBinary(_) => {
let arr = as_fixed_size_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
hex_encode_bytes(&arr, lowercase)?
}
_ => {
return exec_err!(
Expand All @@ -385,7 +375,7 @@ mod test {
use std::sync::Arc;

use arrow::array::{
BinaryArray, DictionaryArray, Int32Array, Int64Array, StringArray,
Array, BinaryArray, DictionaryArray, Int32Array, Int64Array, StringArray,
};
use arrow::{
array::{
Expand Down Expand Up @@ -554,6 +544,56 @@ mod test {
assert_eq!(strings.value(0), expected);
}

#[test]
fn test_spark_hex_binary_no_nulls() {
let input = BinaryArray::from(vec![
b"".as_slice(),
b"\x00\x7f\x80\xff".as_slice(),
b"DataFusion".as_slice(),
]);

let result = super::spark_hex(&[ColumnarValue::Array(Arc::new(input))]).unwrap();
let array = match result {
ColumnarValue::Array(array) => array,
_ => panic!("Expected array"),
};
let strings = as_string_array(&array);

assert_eq!(strings.nulls(), None);
assert_eq!(
strings,
&StringArray::from(vec!["", "007F80FF", "44617461467573696F6E"])
);
}

#[test]
fn test_spark_hex_binary_reuses_input_nulls() {
let input = BinaryArray::from(vec![
Some(b"skip".as_slice()),
None,
Some(b"\x00\xff".as_slice()),
Some(b"hex".as_slice()),
None,
])
.slice(1, 4);
let input_nulls = input.nulls().unwrap().clone();

let result = super::spark_hex(&[ColumnarValue::Array(Arc::new(input))]).unwrap();
let array = match result {
ColumnarValue::Array(array) => array,
_ => panic!("Expected array"),
};
let strings = as_string_array(&array);
let output_nulls = strings.nulls().unwrap();

assert_eq!(output_nulls, &input_nulls);
assert!(output_nulls.inner().ptr_eq(input_nulls.inner()));
assert_eq!(
strings,
&StringArray::from(vec![None, Some("00FF"), Some("686578"), None])
);
}

#[test]
fn test_spark_hex_int64() {
let int_array = Int64Array::from(vec![Some(1), Some(2), None, Some(3)]);
Expand Down
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