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Use Arc<[Buffer]> instead of raw Vec<Buffer> in GenericByteViewArray for faster slice #6427

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Use Arc<[Buffer]> instead of raw Vec<Buffer> in GenericByteViewArray for faster slice #6427

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18e3113
Use `Arc<[Buffer]>` instead of raw `Vec<Buffer>` in `GenericByteViewA…
ShiKaiWi Sep 20, 2024
33eae4b
add benchmark case about view array slice
ShiKaiWi Sep 20, 2024
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2 changes: 1 addition & 1 deletion arrow-array/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@ name = "occupancy"
harness = false

[[bench]]
name = "gc_view_types"
name = "view_types"
harness = false

[[bench]]
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6 changes: 6 additions & 0 deletions arrow-array/benches/gc_view_types.rs → arrow-array/benches/view_types.rs
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Expand Up @@ -42,6 +42,12 @@ fn criterion_benchmark(c: &mut Criterion) {
black_box(sliced.gc());
});
});

c.bench_function("view types slice", |b| {
b.iter(|| {
black_box(array.slice(0, 100_000 / 2));
});
});
}

criterion_group!(benches, criterion_benchmark);
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28 changes: 18 additions & 10 deletions arrow-array/src/array/byte_view_array.rs
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Expand Up @@ -114,7 +114,7 @@ use super::ByteArrayType;
pub struct GenericByteViewArray<T: ByteViewType + ?Sized> {
data_type: DataType,
views: ScalarBuffer<u128>,
buffers: Vec<Buffer>,
buffers: Arc<[Buffer]>,
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What's the rationale for Arc<[Buffer]> vs Vec<Arc>?

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Cloning an Arc is relatively cheap (no allocation), cloning a Vec isn't.

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i get it. However, if i understand correctly, Arc<[Buffer]> means the buffers can be passed around and shared only when they are within single slice, which can be limiting. For example, Can i merge two arrays, combining their Arc<Buffer> s without moving or cloning the buffers?

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@alamb alamb Oct 15, 2024 •
edited
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Can i merge two arrays, combining their Arc s without moving or cloning the buffers?

No -- you would have to create a new Vec<Buffer> (or some other way to get Arc<[Buffer]>)

So while there are some cases where new allocations are required, slicing / cloning is faster

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you would have to create a new Vec<Buffer>

but that would prevent buffer sharing between two arrays, right?

slicing / cloning is faster

cloning yes

slicing -- i didn't see it

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I think the observation is that during StringViewArray::slice, the slice actually happens on the views -- the buffers (that the views can point at) must be copied

Here is the clone of buffers: https://docs.rs/arrow-array/53.1.0/src/arrow_array/array/byte_view_array.rs.html#385

phantom: PhantomData<T>,
nulls: Option<NullBuffer>,
}
Expand Down Expand Up @@ -178,7 +178,7 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
Ok(Self {
data_type: T::DATA_TYPE,
views,
buffers,
buffers: buffers.into(),
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I think we should take impl Into<Arc<[Buffer]>> in this method as well

nulls,
phantom: Default::default(),
})
Expand All @@ -191,14 +191,14 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
/// Safe if [`Self::try_new`] would not error
pub unsafe fn new_unchecked(
views: ScalarBuffer<u128>,
buffers: Vec<Buffer>,
buffers: impl Into<Arc<[Buffer]>>,
nulls: Option<NullBuffer>,
) -> Self {
Self {
data_type: T::DATA_TYPE,
phantom: Default::default(),
views,
buffers,
buffers: buffers.into(),
nulls,
}
}
Expand All @@ -208,7 +208,7 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
Self {
data_type: T::DATA_TYPE,
views: vec![0; len].into(),
buffers: vec![],
buffers: vec![].into(),
nulls: Some(NullBuffer::new_null(len)),
phantom: Default::default(),
}
Expand All @@ -234,7 +234,7 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
}

/// Deconstruct this array into its constituent parts
pub fn into_parts(self) -> (ScalarBuffer<u128>, Vec<Buffer>, Option<NullBuffer>) {
pub fn into_parts(self) -> (ScalarBuffer<u128>, Arc<[Buffer]>, Option<NullBuffer>) {
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This is also a breaking change

(self.views, self.buffers, self.nulls)
}

Expand Down Expand Up @@ -516,7 +516,7 @@ impl<T: ByteViewType + ?Sized> From<ArrayData> for GenericByteViewArray<T> {
Self {
data_type: T::DATA_TYPE,
views,
buffers,
buffers: buffers.into(),
nulls: value.nulls().cloned(),
phantom: Default::default(),
}
Expand Down Expand Up @@ -569,12 +569,20 @@ where
}

impl<T: ByteViewType + ?Sized> From<GenericByteViewArray<T>> for ArrayData {
fn from(mut array: GenericByteViewArray<T>) -> Self {
fn from(array: GenericByteViewArray<T>) -> Self {
let len = array.len();
array.buffers.insert(0, array.views.into_inner());
let new_buffers = {
let mut buffers = Vec::with_capacity(array.buffers.len() + 1);
buffers.push(array.views.into_inner());
for buffer in array.buffers.iter() {
buffers.push(buffer.clone());
}
buffers
};

let builder = ArrayDataBuilder::new(T::DATA_TYPE)
.len(len)
.buffers(array.buffers)
.buffers(new_buffers)
.nulls(array.nulls);

unsafe { builder.build_unchecked() }
Expand Down
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