GH-46178: [R] source_node alignment warning

[thisisnic]

Rationale for this change

There was a warning about unaligned nodes

What changes are included in this PR?

Make them get aligned

Are these changes tested?

Nah, but we should see a lack of warning on CI

Are there any user-facing changes?

Nope

• GitHub Issue: [R] source_node alignment warning #46178

[thisisnic]

@github-actions crossbow submit test-r-linux-sanitizers

[github-actions]

⚠️ GitHub issue #46178 has been automatically assigned in GitHub to PR creator.

[Copilot]

Pull request overview

This PR updates the Arrow R Acero execution plan creation to avoid warnings about unaligned source buffers by configuring plan-wide alignment handling to reallocate unaligned buffers.

Changes:

• Create an acero::QueryOptions instance when building an ExecPlan in R.
• Set query_options.unaligned_buffer_handling to acero::UnalignedBufferHandling::kReallocate.
• Pass the configured QueryOptions into acero::ExecPlan::Make(...).

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[thisisnic]

Nope, this is pedantic, most of our users don't engage with this at this level. The real question isn't whether we should document it but whether there'll likely be user impact. Given we don't see these warnings particularly often on our tests, I'm going to assume minimal impact.

[thisisnic]

@github-actions crossbow submit test-r-linux-sanitizers

[github-actions]

Revision: bf17c95

Submitted crossbow builds: ursacomputing/crossbow @ actions-cb1dab0945

Task	Status
test-r-linux-sanitizers

[jonkeane]

I looked through the asan logs and on main (the latest crossbow run) I see:

2026-06-08T02:07:07.6984909Z /arrow/cpp/src/arrow/acero/source_node.cc:77: An input buffer was poorly aligned.  This could lead to crashes or poor performance on some hardware.  Please ensure that all Acero sources generate aligned buffers, or change the unaligned buffer handling configuration to silence this warning.

and I don't see that on the run on this PR. I will run this against our CRAN release crossbow job too, and if that passes, we are good to merge.

[jonkeane]

@github-actions crossbow submit test-r-macos-as-cran

[github-actions]

Revision: bf17c95

Submitted crossbow builds: ursacomputing/crossbow @ actions-574fe09b49

Task	Status
test-r-macos-as-cran

[thisisnic]

I looked through the asan logs and on main (the latest crossbow run) I see:

2026-06-08T02:07:07.6984909Z /arrow/cpp/src/arrow/acero/source_node.cc:77: An input buffer was poorly aligned.  This could lead to crashes or poor performance on some hardware.  Please ensure that all Acero sources generate aligned buffers, or change the unaligned buffer handling configuration to silence this warning.

and I don't see that on the run on this PR. I will run this against our CRAN release crossbow job too, and if that passes, we are good to merge.

Thanks loads for digging through those logs - I'd meant to do that myself!