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Merged
Jefffrey merged 6 commits into from
Nov 9, 2025
Merged

Make array_reverse faster for List and FixedSizeList #18500

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7f3dc5c
Improve performance of array_reverse 5x by using take, not MutableData
vegarsti Nov 5, 2025
38af34a
Add a test for reversing a FixedSizeList with nulls
vegarsti Nov 5, 2025
ca9319e
Add test with empty arrays
vegarsti Nov 6, 2025
41e1044
Reverse indices directly for FixedSizeList
vegarsti Nov 6, 2025
388ab48
Rework benchmark to have variable sized arrays and nulls
vegarsti Nov 8, 2025
80888ea
Merge branch 'main' into improve-perf-list-reverse
vegarsti Nov 9, 2025
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53 changes: 32 additions & 21 deletions datafusion/functions-nested/src/reverse.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,8 +19,8 @@

use crate::utils::make_scalar_function;
use arrow::array::{
Array, ArrayRef, Capacities, FixedSizeListArray, GenericListArray,
GenericListViewArray, MutableArrayData, OffsetSizeTrait, UInt32Array,
Array, ArrayRef, FixedSizeListArray, GenericListArray, GenericListViewArray,
OffsetSizeTrait, UInt32Array, UInt64Array,
};
use arrow::buffer::{OffsetBuffer, ScalarBuffer};
use arrow::compute::take;
Expand Down Expand Up @@ -155,11 +155,8 @@ fn general_array_reverse<O: OffsetSizeTrait>(
field: &FieldRef,
) -> Result<ArrayRef> {
let values = array.values();
let original_data = values.to_data();
let capacity = Capacities::Array(original_data.len());
let mut offsets = vec![O::usize_as(0)];
let mut mutable =
MutableArrayData::with_capacities(vec![&original_data], false, capacity);
let mut indices: Vec<O> = Vec::with_capacity(values.len());

for (row_index, (&start, &end)) in array.offsets().iter().tuple_windows().enumerate()
{
Expand All @@ -171,18 +168,34 @@ fn general_array_reverse<O: OffsetSizeTrait>(

let mut index = end - O::one();
while index >= start {
mutable.extend(0, index.to_usize().unwrap(), index.to_usize().unwrap() + 1);
indices.push(index);
index = index - O::one();
}
let size = end - start;
offsets.push(offsets[row_index] + size);
}

let data = mutable.freeze();
// Materialize values from underlying array with take
let indices_array: ArrayRef = if O::IS_LARGE {
Arc::new(UInt64Array::from(
indices
.iter()
.map(|i| i.as_usize() as u64)
.collect::<Vec<_>>(),
))
} else {
Arc::new(UInt32Array::from(
indices
.iter()
.map(|i| i.as_usize() as u32)
.collect::<Vec<_>>(),
))
};
Comment on lines +178 to +193
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@vegarsti vegarsti Nov 5, 2025

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This is duplicated for ListView. I figured twice was not enough to extract to a function, but if we find a nicer way to do it, we can improve both.

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@Jefffrey Jefffrey Nov 6, 2025

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It would be nice if we figured out a nicer way of doing this but I still can't figure it out 😅

Went a bit crazy with generics in attempting once but didn't pan out; but it works and the if branch isn't a big deal, though I wonder if it's more efficient to just have Int32/Int64 arrays instead of their unsigned variants to avoid needing a map -> collect 🤔

let values = take(&values, &indices_array, None)?;
Ok(Arc::new(GenericListArray::<O>::try_new(
Arc::clone(field),
OffsetBuffer::<O>::new(offsets.into()),
arrow::array::make_array(data),
values,
array.nulls().cloned(),
)?))
}
Expand Down Expand Up @@ -231,7 +244,7 @@ fn list_view_reverse<O: OffsetSizeTrait>(

// Materialize values from underlying array with take
let indices_array: ArrayRef = if O::IS_LARGE {
Arc::new(arrow::array::UInt64Array::from(
Arc::new(UInt64Array::from(
indices
.iter()
.map(|i| i.as_usize() as u64)
Expand All @@ -245,13 +258,12 @@ fn list_view_reverse<O: OffsetSizeTrait>(
.collect::<Vec<_>>(),
))
};
let values_reversed = take(&values, &indices_array, None)?;

let values = take(&values, &indices_array, None)?;
Ok(Arc::new(GenericListViewArray::<O>::try_new(
Arc::clone(field),
ScalarBuffer::from(new_offsets),
ScalarBuffer::from(new_sizes),
values_reversed,
values,
array.nulls().cloned(),
)?))
}
Expand All @@ -261,30 +273,29 @@ fn fixed_size_array_reverse(
field: &FieldRef,
) -> Result<ArrayRef> {
let values = array.values();
let original_data = values.to_data();
let capacity = Capacities::Array(original_data.len());
let mut mutable =
MutableArrayData::with_capacities(vec![&original_data], false, capacity);
let value_length = array.value_length() as usize;
let mut indices: Vec<u64> = Vec::with_capacity(values.len());
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@Jefffrey Jefffrey Nov 6, 2025

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I do wonder for FSL's if we can take advantage of knowing its a fixed size list to do it in a more efficient way? For example we know a FSL like so:

FSL with fixed length 3:
[[a, b, c], [d, e, f]]

Would always have reverse offsets like so:

[2, 1, 0, 5, 4, 3]

Without even needing to iterate the FSL array itself 🤔

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@vegarsti vegarsti Nov 6, 2025

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Very elegant! Included in 41e1044


for row_index in 0..array.len() {
// skip the null value
if array.is_null(row_index) {
mutable.extend(0, 0, value_length);
indices.push(0);
continue;
}
let start = row_index * value_length;
let end = start + value_length;
for idx in (start..end).rev() {
mutable.extend(0, idx, idx + 1);
indices.push(idx as u64);
}
}

let data = mutable.freeze();
// Materialize values from underlying array with take
let indices_array: ArrayRef = Arc::new(UInt64Array::from(indices));
let values = take(&values, &indices_array, None)?;
Ok(Arc::new(FixedSizeListArray::try_new(
Arc::clone(field),
array.value_length(),
arrow::array::make_array(data),
values,
array.nulls().cloned(),
)?))
}
Expand Down
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