[AURON #2499] perf: avoid identity take in GenerateExec

[lyne7-sc]

Which issue does this PR close?

Closes #2499

Rationale for this change

Avoid redundant generated-array copies during non-outer GenerateExec.

What changes are included in this PR?

• Reuse generated output arrays directly when outer is false.
• Keep the existing take path for outer generation.
• Preserve the child-column take required to duplicate parent rows.

Are there any user-facing changes?

No. This is an internal performance improvement.

How was this patch tested?

Existed unit tests passed.

Benchmarks

The benchmark uses 10,000 input rows with 8 values per row. The reported values are averages of two runs.

Benchmark	Before	After	Improvement
explode_array_i32	0.625 ms	0.567 ms	9.3%
posexplode_array_i32	0.728 ms	0.617 ms	15.3%
explode_map_utf8_i32	1.156 ms	0.544 ms	53.0%
explode_array_i32_parent_null_gaps	0.551 ms	0.526 ms	4.5%

Was this patch authored or co-authored using generative AI tooling?

• Yes
• No

If yes, include: Generated-by: gpt-5.6

ASF guidance: https://www.apache.org/legal/generative-tooling.html

[Copilot]

🟢 Approval recommended

The change is localized and aligns with the existing row-id construction logic; only a minor comment-clarity nit was identified.

Pull request overview

This PR optimizes GenerateExec by skipping an unnecessary Arrow take on generator output columns when outer is false, avoiding redundant array allocations/copies while preserving correctness for outer generation and parent-row duplication.

Changes:

• Reuse generated_outputs.cols directly for non-outer generation to avoid identity take.
• Keep the take path for outer generation where NULL padding is required.

File summaries

File	Description
native-engine/datafusion-ext-plans/src/generate_exec.rs	Avoids redundant identity take on generated output arrays when outer is false.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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[lyne7-sc]

Updated in c26475c.

[slfan1989]

Thanks for this performance improvement!

One process item before merging:
the PR marks generative AI tooling as “Yes”, but the Generated-by field still contains the placeholder.

Please replace it with the actual tool name and version.

LGTM otherwise.

[lyne7-sc]

@slfan1989 Thanks for the review! I've updated the Generated-by field.