GH-43573: [C++] Copy bitmap when casting from string-view to offset string and binary types #44822

crystalxyz · 2024-11-24T03:10:55Z

Rationale for this change

Use CopyBitmap to optimize performance in string casting from string-view to offset string.

What changes are included in this PR?

Originally, the way we create the bitmap is by appending one bit at a time, which is slow. Since casting should not change the values in bitmap, this feature takes advantage of CopyBitmap to create the entire bitmap at once.

Then, to create offsets and buffer array, I use TypedBufferBuilder as suggested in the original comment #43302 (comment).

Are these changes tested?

The original unit tests have passed.

Are there any user-facing changes?

No, the casting behavior should remain unchanged.

closes #43573

GitHub Issue: [C++] Copy bitmap all at once when casting from string-view to offset string and binary types #43573

github-actions · 2024-11-24T03:11:20Z

⚠️ GitHub issue #43573 has been automatically assigned in GitHub to PR creator.

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

mapleFU · 2024-11-24T05:40:37Z

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

+  if (input.offset == output->offset) {
+    output->buffers[0] = input.GetBuffer(0);
+  } else {
+    if (input.buffers[0].data != NULLPTR) {


// When the offsets are different (e.g., due to slice operation), we need to check if // the null bitmap buffer is not null before copying it. The null bitmap buffer can be // null if the input array value does not contain any null value.

Do we also need a comment here?

Can you copy and paste this utility function [1] to this compilation unit and call it from here instead?

[1] https://github.com/apache/arrow/blob/main/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc#L42

(Later the utility could be moved to a .h so it's callable from anywhere and inlinable. But I'm suggesting a copy because it's tricky to name this function in an informative and non-error-prone way.)

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

Co-authored-by: mwish <maplewish117@gmail.com>

felipecrv

This looks great. Asking for some tweaks.

felipecrv · 2024-12-10T13:29:13Z

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

+  if (input.offset == output->offset) {
+    output->buffers[0] = input.GetBuffer(0);
+  } else {
+    if (input.buffers[0].data != NULLPTR) {


Can you copy and paste this utility function [1] to this compilation unit and call it from here instead?

[1] https://github.com/apache/arrow/blob/main/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc#L42

(Later the utility could be moved to a .h so it's callable from anywhere and inlinable. But I'm suggesting a copy because it's tricky to name this function in an informative and non-error-prone way.)

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

mapleFU

General LGTM, thanks!

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

felipecrv · 2025-01-29T17:15:05Z

@mapleFU don't you want take this to the finish line? Unless @CrystalZhou0529 is available to implement the final changes.

crystalxyz · 2025-02-07T19:14:00Z

Thanks for reviewing it! Sorry for falling behind on this PR. I will implement the final changes now.

Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

crystalxyz · 2025-02-07T19:58:04Z

Hi @felipecrv @mapleFU, I have just committed the requested changes. Please take another look and let me know if it looks reasonable!

mapleFU

General LGTM!

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

mapleFU · 2025-02-14T17:22:32Z

@felipecrv Would you mind take a look? Or I just move forward?

mapleFU · 2025-02-20T14:30:51Z

@pitrou @zanmato1984 would you mind take a look? This optimization is not complex

pitrou · 2025-02-20T14:34:12Z

Are the CI failures related?

mapleFU · 2025-02-20T14:47:46Z

Let me rerun to see it

pitrou · 2025-02-20T15:16:56Z

Yeah, GetNullBitmapBuffer is getting defined twice in unity builds, it seems.

pitrou · 2025-02-20T15:37:47Z

The CI failures need fixing but, other than that, this PR is looking very good. I get a 2x improvement on some Python micro-benchmarks:

before:

>>> a = pa.array(([b'foobar']*100+[None])*100, type=pa.binary_view())
>>> b = a.cast(pa.binary())
>>> %timeit a.cast(pa.binary())
136 μs ± 461 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
>>> %timeit b.cast(pa.binary_view())
18.4 μs ± 21 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)

after:

>>> a = pa.array(([b'foobar']*100+[None])*100, type=pa.binary_view())
>>> b = a.cast(pa.binary())
>>> %timeit a.cast(pa.binary())
51.6 μs ± 256 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
>>> %timeit b.cast(pa.binary_view())
19.5 μs ± 458 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)

(also showing the binary -> binary_view conversion for comparison)

mapleFU · 2025-02-20T15:53:47Z

Yeah, GetNullBitmapBuffer is getting defined twice in unity builds, it seems.

Aha scalar_cast_nested.cc also defined a part of this

mapleFU · 2025-02-20T16:03:59Z

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

+    return in_array.GetBuffer(0);
+  }
+
+  if (in_array.offset % 8 == 0) {


Add a SliceBuffer

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

mapleFU · 2025-03-26T09:47:14Z

@pitrou I've move helper fn to a common place, would you mind take a look?

cpp/src/arrow/compute/kernels/scalar_cast_string.cc

pitrou

This mostly looks good to me, I posted a small suggestion for improvement.

pitrou

Thanks for the update! Feel free to merge if CI is green @mapleFU

conbench-apache-arrow · 2025-03-27T21:25:33Z

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit a42edc0.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 23 possible false positives for unstable benchmarks that are known to sometimes produce them.

…fset string and binary types (apache#44822) ### Rationale for this change Use `CopyBitmap` to optimize performance in string casting from string-view to offset string. ### What changes are included in this PR? Originally, the way we create the bitmap is by appending one bit at a time, which is slow. Since casting should not change the values in bitmap, this feature takes advantage of `CopyBitmap` to create the entire bitmap at once. Then, to create offsets and buffer array, I use `TypedBufferBuilder` as suggested in the original comment apache#43302 (comment). ### Are these changes tested? The original unit tests have passed. ### Are there any user-facing changes? No, the casting behavior should remain unchanged. closes [ apache#43573 ](apache#43573) * GitHub Issue: apache#43573 Lead-authored-by: Crystal Zhou <crystal.zhouxiaoyue@hotmail.com> Co-authored-by: mwish <maplewish117@gmail.com> Co-authored-by: Crystal Zhou <45134936+CrystalZhou0529@users.noreply.github.com> Co-authored-by: Crystal <45134936+CrystalZhou0529@users.noreply.github.com> Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com> Signed-off-by: mwish <maplewish117@gmail.com>

Optimize string view to offset string cast

14d7d5c

github-actions bot added the Component: C++ label Nov 24, 2024

crystalxyz marked this pull request as draft November 24, 2024 03:11

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pitrou requested a review from felipecrv November 27, 2024 13:29

crystalxyz and others added 3 commits November 30, 2024 17:41

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc

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Co-authored-by: mwish <maplewish117@gmail.com>

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc

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Co-authored-by: mwish <maplewish117@gmail.com>

Fix allocation of data buffer size

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crystalxyz and others added 2 commits February 7, 2025 14:18

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc

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Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc

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Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

github-actions bot added awaiting change review Awaiting change review and removed awaiting changes Awaiting changes labels Feb 7, 2025

Copy GetNullBitmapBuffer to own file and call it

5c262a9

mapleFU approved these changes Feb 8, 2025

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mapleFU requested a review from felipecrv February 14, 2025 17:20

Merge branch 'main' into pr-44822

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Trying to fix ci

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mapleFU requested a review from pitrou February 25, 2025 13:27

mapleFU added 2 commits March 26, 2025 17:40

Merge branch 'main' into 43573-copy-bitmap-when-cast-string

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move GetOrCopyNullBitmapBuffer to util_internal.h

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using VisitVoid instead of VisitStatus

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mapleFU force-pushed the 43573-copy-bitmap-when-cast-string branch from 88c039d to 36c6001 Compare March 27, 2025 03:05

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[C++] Copy bitmap all at once when casting from string-view to offset string and binary types #43573

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GH-43573: [C++] Copy bitmap when casting from string-view to offset string and binary types #44822

GH-43573: [C++] Copy bitmap when casting from string-view to offset string and binary types #44822

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