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perf: copy bitmaps a word at a time in pre_selection_scatter #25494

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perf: copy bitmaps a word at a time in pre_selection_scatter #25494

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48 changes: 42 additions & 6 deletions datafusion/physical-expr/src/expressions/binary.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ use std::hash::Hash;
use std::sync::Arc;

use arrow::array::*;
use arrow::buffer::NullBuffer;
use arrow::compute::kernels::boolean::{and_kleene, or_kleene};
use arrow::compute::kernels::concat_elements::concat_elements_dyn;
use arrow::compute::{SlicesIterator, cast, filter, filter_record_batch};
Expand Down Expand Up @@ -1360,21 +1361,56 @@ fn pre_selection_scatter(
let mut last_end = 0;
match right_result {
Some(right_result) => {
// Borrow the RHS buffers once. `BooleanArray::slice` clones and
// drops an `Arc` for every run, which dominates this loop when the
// mask selects many short runs.
let right_values = right_result.values();
let right_offset = right_values.offset();
let right_bytes = right_values.values();
let right_nulls = right_result.nulls();

let mut values = BooleanBufferBuilder::new(result_len);

@kosiew kosiew Oct 9, 2026

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Could we move result_array_builder initialization into the None branch? The new Some branch allocates its own bitmap builder and returns without using the original one, so this would avoid an unnecessary allocation and free.

// Only build a validity bitmap when the RHS has nulls. Otherwise
// every run pays a second pass to write an all-ones mask that is
// then discarded.
let mut validity = right_nulls.map(|_| BooleanBufferBuilder::new(result_len));

SlicesIterator::new(mask).for_each(|(start, end)| {
if start > last_end {
result_array_builder.append_n(start - last_end, fill_value);
let gap = start - last_end;
values.append_n(gap, fill_value);
if let Some(v) = validity.as_mut() {
v.append_n(gap, true);
}
}

// Copy the selected RHS slice.
// Both sides are bit-packed, so copy the run a word at a
// time. Iterating the RHS would yield one `Option<bool>` and
// set one bit per row.
let len = end - start;
right_result
.slice(right_array_pos, len)
.iter()
.for_each(|v| result_array_builder.append_option(v));
let from = right_offset + right_array_pos;
values.append_packed_range(from..from + len, right_bytes);

@kosiew kosiew Oct 9, 2026

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Could we add a scatter regression test covering nullable RHS values, non-byte-aligned offsets, runs crossing byte and 64-bit boundaries, and leading, intermediate, and trailing gaps with both fill values? Please include independently offset value and validity buffers, since ordinary slices usually share the same offset, and compare the output against a simple row-wise reference.

if let (Some(v), Some(nulls)) = (validity.as_mut(), right_nulls) {
let nb = nulls.inner();
let nfrom = nb.offset() + right_array_pos;
v.append_packed_range(nfrom..nfrom + len, nb.values());
}

right_array_pos += len;
last_end = end;
});

if last_end < result_len {
let gap = result_len - last_end;
values.append_n(gap, fill_value);
if let Some(v) = validity.as_mut() {
v.append_n(gap, true);
}
}

let nulls = validity.map(|mut v| NullBuffer::new(v.finish()));
let boolean_result = BooleanArray::new(values.finish(), nulls);
return Ok(ColumnarValue::Array(Arc::new(boolean_result)));
}
None => SlicesIterator::new(mask).for_each(|(start, end)| {
if start > last_end {
Expand Down
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