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Merged
Jefffrey merged 2 commits into from
Feb 1, 2026
Merged

perf: Optimize scalar path for chr function #20073

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93bfdc2
perf: Optimize scalar path for chr function
kumarUjjawal Jan 30, 2026
c3b33ca
refactor for match and add slt
kumarUjjawal Jan 31, 2026
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31 changes: 26 additions & 5 deletions datafusion/functions/benches/chr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ extern crate criterion;

use arrow::{array::PrimitiveArray, datatypes::Int64Type};
use criterion::{Criterion, criterion_group, criterion_main};
use datafusion_common::ScalarValue;
use datafusion_expr::{ColumnarValue, ScalarFunctionArgs};
use datafusion_functions::string::chr;
use rand::{Rng, SeedableRng};
Expand All @@ -35,11 +36,32 @@ pub fn seedable_rng() -> StdRng {
}

fn criterion_benchmark(c: &mut Criterion) {
let cot_fn = chr();
let chr_fn = chr();
let config_options = Arc::new(ConfigOptions::default());

// Scalar benchmarks
c.bench_function("chr/scalar", |b| {
let args = vec![ColumnarValue::Scalar(ScalarValue::Int64(Some(65)))];
let arg_fields = vec![Field::new("arg_0", DataType::Int64, true).into()];
b.iter(|| {
black_box(
chr_fn
.invoke_with_args(ScalarFunctionArgs {
args: args.clone(),
arg_fields: arg_fields.clone(),
number_rows: 1,
return_field: Field::new("f", DataType::Utf8, true).into(),
config_options: Arc::clone(&config_options),
})
.unwrap(),
)
})
});

let size = 1024;
let input: PrimitiveArray<Int64Type> = {
let null_density = 0.2;
let mut rng = StdRng::seed_from_u64(42);
let mut rng = seedable_rng();
(0..size)
.map(|_| {
if rng.random::<f32>() < null_density {
Expand All @@ -57,12 +79,11 @@ fn criterion_benchmark(c: &mut Criterion) {
.enumerate()
.map(|(idx, arg)| Field::new(format!("arg_{idx}"), arg.data_type(), true).into())
.collect::<Vec<_>>();
let config_options = Arc::new(ConfigOptions::default());

c.bench_function("chr", |b| {
c.bench_function("chr/array", |b| {
b.iter(|| {
black_box(
cot_fn
chr_fn
.invoke_with_args(ScalarFunctionArgs {
args: args.clone(),
arg_fields: arg_fields.clone(),
Expand Down
126 changes: 91 additions & 35 deletions datafusion/functions/src/string/chr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,24 +18,21 @@
use std::any::Any;
use std::sync::Arc;

use arrow::array::ArrayRef;
use arrow::array::GenericStringBuilder;
use arrow::array::{ArrayRef, GenericStringBuilder, Int64Array};
use arrow::datatypes::DataType;
use arrow::datatypes::DataType::Int64;
use arrow::datatypes::DataType::Utf8;

use crate::utils::make_scalar_function;
use datafusion_common::cast::as_int64_array;
use datafusion_common::{Result, exec_err};
use datafusion_common::utils::take_function_args;
use datafusion_common::{Result, ScalarValue, exec_err, internal_err};
use datafusion_expr::{ColumnarValue, Documentation, Volatility};
use datafusion_expr::{ScalarFunctionArgs, ScalarUDFImpl, Signature};
use datafusion_macros::user_doc;

/// Returns the character with the given code.
/// chr(65) = 'A'
fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {
let integer_array = as_int64_array(&args[0])?;

fn chr_array(integer_array: &Int64Array) -> Result<ArrayRef> {
let mut builder = GenericStringBuilder::<i32>::with_capacity(
integer_array.len(),
// 1 byte per character, assuming that is the common case
Expand All @@ -56,15 +53,11 @@ fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {

return exec_err!("invalid Unicode scalar value: {integer}");
}
None => {
builder.append_null();
}
None => builder.append_null(),
}
}

let result = builder.finish();

Ok(Arc::new(result) as ArrayRef)
Ok(Arc::new(builder.finish()) as ArrayRef)
}

#[user_doc(
Expand Down Expand Up @@ -119,7 +112,32 @@ impl ScalarUDFImpl for ChrFunc {
}

fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
make_scalar_function(chr, vec![])(&args.args)
let [arg] = take_function_args(self.name(), args.args)?;

match arg {
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@Jefffrey Jefffrey Jan 30, 2026

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match arg {
    ColumnarValue::Scalar(ScalarValue::Int64(Some(code_point))) => {
        if let Ok(u) = u32::try_from(code_point)
            && let Some(c) = core::char::from_u32(u)
        {
            Ok(ColumnarValue::Scalar(ScalarValue::Utf8(Some(
                   c.to_string(),
                ))))
            } else {
                exec_err!("invalid Unicode scalar value: {code_point}")
            }
    }
    ColumnarValue::Scalar(ScalarValue::Int64(None)) => {
        Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None)))
    }
    ColumnarValue::Array(array) => {
        Ok(ColumnarValue::Array(chr(&[array])?))
    }
    _ => internal_err!("..."),
}
  • Easier to fold into match like this since we accept only one datatype; also unnecessary to double check the array datatype
  • Also worth looking into refactoring chr() function; no reason to pass in a slice when we can just pass the array

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@kumarUjjawal kumarUjjawal Jan 31, 2026

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Thanks!

ColumnarValue::Scalar(ScalarValue::Int64(Some(code_point))) => {
if let Ok(u) = u32::try_from(code_point)
&& let Some(c) = core::char::from_u32(u)
{
Ok(ColumnarValue::Scalar(ScalarValue::Utf8(Some(
c.to_string(),
))))
} else {
exec_err!("invalid Unicode scalar value: {code_point}")
}
}
ColumnarValue::Scalar(ScalarValue::Int64(None)) => {
Ok(ColumnarValue::Scalar(ScalarValue::Utf8(None)))
}
ColumnarValue::Array(array) => {
let integer_array = as_int64_array(&array)?;
Ok(ColumnarValue::Array(chr_array(integer_array)?))
}
other => internal_err!(
"Unexpected data type {:?} for function chr",
other.data_type()
),
}
}

fn documentation(&self) -> Option<&Documentation> {
Expand All @@ -130,13 +148,27 @@ impl ScalarUDFImpl for ChrFunc {
#[cfg(test)]
mod tests {
use super::*;

use arrow::array::{Array, Int64Array, StringArray};
use arrow::datatypes::Field;
use datafusion_common::assert_contains;
use datafusion_common::config::ConfigOptions;
use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl};

fn invoke_chr(arg: ColumnarValue, number_rows: usize) -> Result<ColumnarValue> {
ChrFunc::new().invoke_with_args(ScalarFunctionArgs {
args: vec![arg],
arg_fields: vec![Field::new("a", Int64, true).into()],
number_rows,
return_field: Field::new("f", Utf8, true).into(),
config_options: Arc::new(ConfigOptions::default()),
})
}

#[test]
fn test_chr_normal() {
let input = Arc::new(Int64Array::from(vec![
Some(0), // null
Some(0), // \u{0000}
Some(65), // A
Some(66), // B
Some(67), // C
Expand All @@ -149,8 +181,13 @@ mod tests {
Some(9), // tab
Some(0x10FFFF), // 0x10FFFF, the largest Unicode code point
]));
let result = chr(&[input]).unwrap();
let string_array = result.as_any().downcast_ref::<StringArray>().unwrap();

let result = invoke_chr(ColumnarValue::Array(input), 12).unwrap();
let ColumnarValue::Array(arr) = result else {
panic!("Expected array");
};
let string_array = arr.as_any().downcast_ref::<StringArray>().unwrap();

let expected = [
"\u{0000}",
"A",
Expand All @@ -174,55 +211,48 @@ mod tests {

#[test]
fn test_chr_error() {
// invalid Unicode code points (too large)
let input = Arc::new(Int64Array::from(vec![i64::MAX]));
let result = chr(&[input]);
let result = invoke_chr(ColumnarValue::Array(input), 1);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
"invalid Unicode scalar value: 9223372036854775807"
);

// invalid Unicode code points (too large) case 2
let input = Arc::new(Int64Array::from(vec![0x10FFFF + 1]));
let result = chr(&[input]);
let result = invoke_chr(ColumnarValue::Array(input), 1);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
"invalid Unicode scalar value: 1114112"
);

// invalid Unicode code points (surrogate code point)
// link: <https://learn.microsoft.com/en-us/globalization/encoding/unicode-standard#surrogate-pairs>
let input = Arc::new(Int64Array::from(vec![0xD800 + 1]));
let result = chr(&[input]);
let result = invoke_chr(ColumnarValue::Array(input), 1);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
"invalid Unicode scalar value: 55297"
);

// negative input
let input = Arc::new(Int64Array::from(vec![i64::MIN + 2i64])); // will be 2 if cast to u32
let result = chr(&[input]);
let input = Arc::new(Int64Array::from(vec![i64::MIN + 2i64]));
let result = invoke_chr(ColumnarValue::Array(input), 1);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
"invalid Unicode scalar value: -9223372036854775806"
);

// negative input case 2
let input = Arc::new(Int64Array::from(vec![-1]));
let result = chr(&[input]);
let result = invoke_chr(ColumnarValue::Array(input), 1);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
"invalid Unicode scalar value: -1"
);

// one error with valid values after
let input = Arc::new(Int64Array::from(vec![65, -1, 66])); // A, -1, B
let result = chr(&[input]);
let input = Arc::new(Int64Array::from(vec![65, -1, 66]));
let result = invoke_chr(ColumnarValue::Array(input), 3);
assert!(result.is_err());
assert_contains!(
result.err().unwrap().to_string(),
Expand All @@ -232,10 +262,36 @@ mod tests {

#[test]
fn test_chr_empty() {
// empty input array
let input = Arc::new(Int64Array::from(Vec::<i64>::new()));
let result = chr(&[input]).unwrap();
let string_array = result.as_any().downcast_ref::<StringArray>().unwrap();
let result = invoke_chr(ColumnarValue::Array(input), 0).unwrap();
let ColumnarValue::Array(arr) = result else {
panic!("Expected array");
};
let string_array = arr.as_any().downcast_ref::<StringArray>().unwrap();
assert_eq!(string_array.len(), 0);
}

#[test]
fn test_chr_scalar() {
let result =
invoke_chr(ColumnarValue::Scalar(ScalarValue::Int64(Some(65))), 1).unwrap();

match result {
ColumnarValue::Scalar(ScalarValue::Utf8(Some(s))) => {
assert_eq!(s, "A");
}
other => panic!("Unexpected result: {other:?}"),
}
}

#[test]
fn test_chr_scalar_null() {
let result =
invoke_chr(ColumnarValue::Scalar(ScalarValue::Int64(None)), 1).unwrap();

match result {
ColumnarValue::Scalar(ScalarValue::Utf8(None)) => {}
other => panic!("Unexpected result: {other:?}"),
}
}
}
10 changes: 10 additions & 0 deletions datafusion/sqllogictest/test_files/expr.slt
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Expand Up @@ -432,6 +432,16 @@ SELECT chr(CAST(0 AS int))
statement error DataFusion error: Execution error: invalid Unicode scalar value: 9223372036854775807
SELECT chr(CAST(9223372036854775807 AS bigint))

statement error DataFusion error: Execution error: invalid Unicode scalar value: 1114112
SELECT chr(CAST(1114112 AS bigint))

statement error DataFusion error: Execution error: invalid Unicode scalar value: -1
SELECT chr(CAST(-1 AS bigint))

# surrogate code point (invalid scalar value)
statement error DataFusion error: Execution error: invalid Unicode scalar value: 55297
SELECT chr(CAST(55297 AS bigint))

query T
SELECT concat('a','b','c')
----
Expand Down