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perf: optimize spark_hex dictionary path by avoiding dictionary expansion #19832

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3b465c3
optimize spark_hex dictionary path
lyne7-sc Jan 15, 2026
8b5087e
cargo fmt
lyne7-sc Jan 15, 2026
62d2912
Merge branch 'apache:main' into perf/spark_hex_dictionary
lyne7-sc Jan 16, 2026
ba8d1ee
refactor hex_encode_bytes/hex_encode_int64 && add datatype for dictio…
lyne7-sc Jan 16, 2026
0946546
Merge branch 'apache:main' into perf/spark_hex_dictionary
lyne7-sc Jan 17, 2026
dcde0f8
update slt to dictionary(binary)
lyne7-sc Jan 17, 2026
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164 changes: 112 additions & 52 deletions datafusion/spark/src/function/math/hex.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ use std::any::Any;
use std::str::from_utf8_unchecked;
use std::sync::Arc;

use arrow::array::{Array, BinaryArray, Int64Array, StringArray, StringBuilder};
use arrow::array::{Array, ArrayRef, StringBuilder};
use arrow::datatypes::DataType;
use arrow::{
array::{as_dictionary_array, as_largestring_array, as_string_array},
Expand Down Expand Up @@ -92,11 +92,13 @@ impl ScalarUDFImpl for SparkHex {
&self.signature
}

fn return_type(
&self,
_arg_types: &[DataType],
) -> datafusion_common::Result<DataType> {
Ok(DataType::Utf8)
fn return_type(&self, arg_types: &[DataType]) -> datafusion_common::Result<DataType> {
Ok(match &arg_types[0] {
DataType::Dictionary(key_type, _) => {
DataType::Dictionary(key_type.clone(), Box::new(DataType::Utf8))
}
_ => DataType::Utf8,
})
}

fn invoke_with_args(
Expand Down Expand Up @@ -136,7 +138,7 @@ fn hex_encode_bytes<'a, I, T>(
iter: I,
lowercase: bool,
len: usize,
) -> Result<ColumnarValue, DataFusionError>
) -> Result<ArrayRef, DataFusionError>
where
I: Iterator<Item = Option<T>>,
T: AsRef<[u8]> + 'a,
Expand Down Expand Up @@ -166,14 +168,14 @@ where
}
}

Ok(ColumnarValue::Array(Arc::new(builder.finish())))
Ok(Arc::new(builder.finish()))
}

/// Generic hex encoding for int64 type
fn hex_encode_int64<I>(iter: I, len: usize) -> Result<ColumnarValue, DataFusionError>
where
I: Iterator<Item = Option<i64>>,
{
fn hex_encode_int64(
iter: impl Iterator<Item = Option<i64>>,
len: usize,
) -> Result<ArrayRef, DataFusionError> {
let mut builder = StringBuilder::with_capacity(len, len * 16);

for v in iter {
Expand All @@ -189,7 +191,7 @@ where
}
}

Ok(ColumnarValue::Array(Arc::new(builder.finish())))
Ok(Arc::new(builder.finish()))
}

/// Spark-compatible `hex` function
Expand All @@ -215,55 +217,109 @@ pub fn compute_hex(
ColumnarValue::Array(array) => match array.data_type() {
DataType::Int64 => {
let array = as_int64_array(array)?;
hex_encode_int64(array.iter(), array.len())
Ok(ColumnarValue::Array(hex_encode_int64(
array.iter(),
array.len(),
)?))
}
DataType::Utf8 => {
let array = as_string_array(array);
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::Utf8View => {
let array = as_string_view_array(array)?;
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::LargeUtf8 => {
let array = as_largestring_array(array);
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::Binary => {
let array = as_binary_array(array)?;
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::LargeBinary => {
let array = as_large_binary_array(array)?;
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::FixedSizeBinary(_) => {
let array = as_fixed_size_binary_array(array)?;
hex_encode_bytes(array.iter(), lowercase, array.len())
Ok(ColumnarValue::Array(hex_encode_bytes(
array.iter(),
lowercase,
array.len(),
)?))
}
DataType::Dictionary(_, value_type) => {
DataType::Dictionary(key_type, _) => {
if **key_type != DataType::Int32 {
return exec_err!(
"hex only supports Int32 dictionary keys, get: {}",
key_type
);
}

let dict = as_dictionary_array::<Int32Type>(&array);
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@Jefffrey Jefffrey Jan 16, 2026

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nit: we should have some check that the dictionary has i32 key type, otherwise this will panic

let dict_values = dict.values();

match **value_type {
let encoded_values = match dict_values.data_type() {
DataType::Int64 => {
let arr = dict.downcast_dict::<Int64Array>().unwrap();
hex_encode_int64(arr.into_iter(), dict.len())
let arr = as_int64_array(dict_values)?;
hex_encode_int64(arr.iter(), arr.len())?
}
DataType::Utf8 => {
let arr = dict.downcast_dict::<StringArray>().unwrap();
hex_encode_bytes(arr.into_iter(), lowercase, dict.len())
let arr = as_string_array(dict_values);
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
DataType::LargeUtf8 => {
let arr = as_largestring_array(dict_values);
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
DataType::Utf8View => {
let arr = as_string_view_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
DataType::Binary => {
let arr = dict.downcast_dict::<BinaryArray>().unwrap();
hex_encode_bytes(arr.into_iter(), lowercase, dict.len())
let arr = as_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
DataType::LargeBinary => {
let arr = as_large_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
DataType::FixedSizeBinary(_) => {
let arr = as_fixed_size_binary_array(dict_values)?;
hex_encode_bytes(arr.iter(), lowercase, arr.len())?
}
_ => {
exec_err!(
return exec_err!(
"hex got an unexpected argument type: {}",
array.data_type()
)
dict_values.data_type()
);
}
}
};

let new_dict = dict.with_values(encoded_values);
Ok(ColumnarValue::Array(Arc::new(new_dict)))
}
_ => exec_err!("hex got an unexpected argument type: {}", array.data_type()),
},
Expand All @@ -279,11 +335,12 @@ mod test {
use arrow::array::{DictionaryArray, Int32Array, Int64Array, StringArray};
use arrow::{
array::{
BinaryDictionaryBuilder, PrimitiveDictionaryBuilder, StringBuilder,
StringDictionaryBuilder, as_string_array,
BinaryDictionaryBuilder, PrimitiveDictionaryBuilder, StringDictionaryBuilder,
as_string_array,
},
datatypes::{Int32Type, Int64Type},
};
use datafusion_common::cast::as_dictionary_array;
use datafusion_expr::ColumnarValue;

#[test]
Expand All @@ -295,12 +352,12 @@ mod test {
input_builder.append_value("rust");
let input = input_builder.finish();

let mut string_builder = StringBuilder::new();
string_builder.append_value("6869");
string_builder.append_value("627965");
string_builder.append_null();
string_builder.append_value("72757374");
let expected = string_builder.finish();
let mut expected_builder = StringDictionaryBuilder::<Int32Type>::new();
expected_builder.append_value("6869");
expected_builder.append_value("627965");
expected_builder.append_null();
expected_builder.append_value("72757374");
let expected = expected_builder.finish();

let columnar_value = ColumnarValue::Array(Arc::new(input));
let result = super::spark_hex(&[columnar_value]).unwrap();
Expand All @@ -310,7 +367,7 @@ mod test {
_ => panic!("Expected array"),
};

let result = as_string_array(&result);
let result = as_dictionary_array(&result).unwrap();

assert_eq!(result, &expected);
}
Expand All @@ -324,12 +381,12 @@ mod test {
input_builder.append_value(3);
let input = input_builder.finish();

let mut string_builder = StringBuilder::new();
string_builder.append_value("1");
string_builder.append_value("2");
string_builder.append_null();
string_builder.append_value("3");
let expected = string_builder.finish();
let mut expected_builder = StringDictionaryBuilder::<Int32Type>::new();
expected_builder.append_value("1");
expected_builder.append_value("2");
expected_builder.append_null();
expected_builder.append_value("3");
let expected = expected_builder.finish();

let columnar_value = ColumnarValue::Array(Arc::new(input));
let result = super::spark_hex(&[columnar_value]).unwrap();
Expand All @@ -339,7 +396,7 @@ mod test {
_ => panic!("Expected array"),
};

let result = as_string_array(&result);
let result = as_dictionary_array(&result).unwrap();

assert_eq!(result, &expected);
}
Expand All @@ -353,7 +410,7 @@ mod test {
input_builder.append_value("3");
let input = input_builder.finish();

let mut expected_builder = StringBuilder::new();
let mut expected_builder = StringDictionaryBuilder::<Int32Type>::new();
expected_builder.append_value("31");
expected_builder.append_value("6A");
expected_builder.append_null();
Expand All @@ -368,7 +425,7 @@ mod test {
_ => panic!("Expected array"),
};

let result = as_string_array(&result);
let result = as_dictionary_array(&result).unwrap();

assert_eq!(result, &expected);
}
Expand Down Expand Up @@ -425,8 +482,11 @@ mod test {
_ => panic!("Expected array"),
};

let result = as_string_array(&result);
let expected = StringArray::from(vec![Some("20"), None, None]);
let result = as_dictionary_array(&result).unwrap();

let keys = Int32Array::from(vec![Some(0), None, Some(1)]);
let vals = StringArray::from(vec![Some("20"), None]);
let expected = DictionaryArray::new(keys, Arc::new(vals));

assert_eq!(&expected, result);
}
Expand Down
20 changes: 20 additions & 0 deletions datafusion/sqllogictest/test_files/spark/math/hex.slt
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Original file line number Diff line number Diff line change
Expand Up @@ -63,3 +63,23 @@ query T
SELECT hex(arrow_cast('test', 'LargeBinary')) as lar_b;
----
74657374

statement ok
CREATE TABLE t_dict_binary AS
SELECT arrow_cast(column1, 'Dictionary(Int32, Binary)') as dict_col
FROM VALUES ('foo'), ('bar'), ('foo'), (NULL), ('baz'), ('bar');

query T
SELECT hex(dict_col) FROM t_dict_binary;
----
666F6F
626172
666F6F
NULL
62617A
626172

query T
SELECT arrow_typeof(hex(dict_col)) FROM t_dict_binary LIMIT 1;
----
Dictionary(Int32, Utf8)