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Optimize memory footprint of view arrays from ScalarValue::to_array_of_size #19441

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Merged
Jefffrey merged 1 commit into from
Dec 23, 2025
Merged

Optimize memory footprint of view arrays from ScalarValue::to_array_of_size #19441

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68 changes: 51 additions & 17 deletions datafusion/common/src/scalar/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -57,19 +57,20 @@ use crate::utils::SingleRowListArrayBuilder;
use crate::{_internal_datafusion_err, arrow_datafusion_err};
use arrow::array::{
Array, ArrayData, ArrayRef, ArrowNativeTypeOp, ArrowPrimitiveType, AsArray,
BinaryArray, BinaryViewArray, BooleanArray, Date32Array, Date64Array, Decimal32Array,
Decimal64Array, Decimal128Array, Decimal256Array, DictionaryArray,
DurationMicrosecondArray, DurationMillisecondArray, DurationNanosecondArray,
DurationSecondArray, FixedSizeBinaryArray, FixedSizeBinaryBuilder,
FixedSizeListArray, Float16Array, Float32Array, Float64Array, GenericListArray,
Int8Array, Int16Array, Int32Array, Int64Array, IntervalDayTimeArray,
IntervalMonthDayNanoArray, IntervalYearMonthArray, LargeBinaryArray, LargeListArray,
LargeStringArray, ListArray, MapArray, MutableArrayData, OffsetSizeTrait,
PrimitiveArray, Scalar, StringArray, StringViewArray, StructArray,
Time32MillisecondArray, Time32SecondArray, Time64MicrosecondArray,
Time64NanosecondArray, TimestampMicrosecondArray, TimestampMillisecondArray,
TimestampNanosecondArray, TimestampSecondArray, UInt8Array, UInt16Array, UInt32Array,
UInt64Array, UnionArray, new_empty_array, new_null_array,
BinaryArray, BinaryViewArray, BinaryViewBuilder, BooleanArray, Date32Array,
Date64Array, Decimal32Array, Decimal64Array, Decimal128Array, Decimal256Array,
DictionaryArray, DurationMicrosecondArray, DurationMillisecondArray,
DurationNanosecondArray, DurationSecondArray, FixedSizeBinaryArray,
FixedSizeBinaryBuilder, FixedSizeListArray, Float16Array, Float32Array, Float64Array,
GenericListArray, Int8Array, Int16Array, Int32Array, Int64Array,
IntervalDayTimeArray, IntervalMonthDayNanoArray, IntervalYearMonthArray,
LargeBinaryArray, LargeListArray, LargeStringArray, ListArray, MapArray,
MutableArrayData, OffsetSizeTrait, PrimitiveArray, Scalar, StringArray,
StringViewArray, StringViewBuilder, StructArray, Time32MillisecondArray,
Time32SecondArray, Time64MicrosecondArray, Time64NanosecondArray,
TimestampMicrosecondArray, TimestampMillisecondArray, TimestampNanosecondArray,
TimestampSecondArray, UInt8Array, UInt16Array, UInt32Array, UInt64Array, UnionArray,
new_empty_array, new_null_array,
};
use arrow::buffer::{BooleanBuffer, ScalarBuffer};
use arrow::compute::kernels::cast::{CastOptions, cast_with_options};
Expand Down Expand Up @@ -3027,7 +3028,13 @@ impl ScalarValue {
},
ScalarValue::Utf8View(e) => match e {
Some(value) => {
Arc::new(StringViewArray::from_iter_values(repeat_n(value, size)))
let mut builder =
StringViewBuilder::with_capacity(size).with_deduplicate_strings();
for _ in 0..size {
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@comphead comphead Dec 23, 2025

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🤔 we should prob have some kind of append_n to remove this boilerplate, in some future for arrow-rs

builder.append_value(value);
}
let array = builder.finish();
Arc::new(array)
Comment on lines +3031 to +3037
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@Jefffrey Jefffrey Dec 21, 2025

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Technically we could further optimize this by manually calling StringViewArray::try_new with correct data and avoid need to hash as part of the builder; felt that might get too into the weeds of arrow-rs code, so stuck with this simpler approach

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@Jefffrey Jefffrey Dec 21, 2025

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Actually if we have a benchmark maybe it could be worth testing out if there is a performance gain by doing this? 🤔

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@alamb alamb Dec 24, 2025

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Update - here is the tracking ticket (thanks @Jefffrey )

}
None => new_null_array(&DataType::Utf8View, size),
},
Expand All @@ -3042,9 +3049,15 @@ impl ScalarValue {
None => new_null_array(&DataType::Binary, size),
},
ScalarValue::BinaryView(e) => match e {
Some(value) => Arc::new(
repeat_n(Some(value.as_slice()), size).collect::<BinaryViewArray>(),
),
Some(value) => {
let mut builder =
BinaryViewBuilder::with_capacity(size).with_deduplicate_strings();
for _ in 0..size {
builder.append_value(value);
}
let array = builder.finish();
Arc::new(array)
}
None => new_null_array(&DataType::BinaryView, size),
},
ScalarValue::FixedSizeBinary(s, e) => match e {
Expand Down Expand Up @@ -9232,6 +9245,27 @@ mod tests {
}
}

#[test]
fn test_views_minimize_memory() {
let value = "this string is longer than 12 bytes".to_string();

let scalar = ScalarValue::Utf8View(Some(value.clone()));
let array = scalar.to_array_of_size(10).unwrap();
let array = array.as_string_view();
let buffers = array.data_buffers();
assert_eq!(1, buffers.len());
// Ensure we only have a single copy of the value string
assert_eq!(value.len(), buffers[0].len());
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@Jefffrey Jefffrey Dec 21, 2025

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On main this assert fails as the data buffer would be 10 * value.len(); with this fix we only have a single copy of the full string in the child buffer, minimizing memory footprint of the output array


// Same but for BinaryView
let scalar = ScalarValue::BinaryView(Some(value.bytes().collect()));
let array = scalar.to_array_of_size(10).unwrap();
let array = array.as_binary_view();
let buffers = array.data_buffers();
assert_eq!(1, buffers.len());
assert_eq!(value.len(), buffers[0].len());
}

#[test]
fn test_convert_array_to_scalar_vec() {
// 1: Regular ListArray
Expand Down