Avoid redundant allocations in struct layout reader

[joseph-isaacs]

Pre-size the dtype and name vectors to their final length and push the validity entry first, instead of collecting at field-count capacity and then insert(0, ..).

The previous code collected each Vec at exact field-count capacity, then insert(0, ..) forced a reallocation and an O(n) shift of every element. Both are now gone.

Checks

• cargo build -p vortex-layout ✅

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will improve performance by 11.17%

⚡ 1 improved benchmark
✅ 1669 untouched benchmarks
⏩ 44 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	true_count_vortex_buffer[128]	580.6 ns	522.2 ns	+11.17%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing avoid-struct-reader-allocs (562cc93) with develop (c5e075a)}

Footnotes

1. 44 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

Polar Signals Profiling Results

Latest Run

Status	Commit	Job	Attempt	Link
🟢 Done	562cc93		1	Explore Profiling Data

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Powered by Polar Signals Cloud

[github-actions]

Benchmarks: Vortex queries 📖

Verdict: No clear signal (low confidence)
Attributed Vortex impact: +1.1%
Engines: DataFusion No clear signal (+6.2%, low confidence) · DuckDB No clear signal (-3.7%, low confidence)
Vortex (geomean): 1.000x ➖
Parquet (geomean): 0.995x ➖
Shifts: Parquet (control) -0.5% · Median polish -0.5%

How to read Verdict and Engines

• Verdict: Overall PR-level signal after subtracting baseline drift estimated from Parquet control rows. It can be Likely improvement, Likely regression, or No clear signal.
• Engines: Per-engine attribution. DataFusion is compared against DataFusion/Parquet controls; DuckDB is compared against DuckDB/Parquet controls. This answers whether each engine improved or regressed independently.
• Confidence: Based on directional consistency, share of rows above the noise floor, and control-run noise.

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datafusion / vortex-file-compressed (1.040x ➖, 0↑ 0↓)

name	PR 562cc93 (ns)	base c5e075a (ns)	ratio (PR/base)
vortex_q00/datafusion:vortex-file-compressed	9794691	9222307	1.06
vortex_q01/datafusion:vortex-file-compressed	6110161	6003507	1.02

datafusion / parquet (0.979x ➖, 0↑ 0↓)

name	PR 562cc93 (ns)	base c5e075a (ns)	ratio (PR/base)
vortex_q00/datafusion:parquet	19672299	20168593	0.98
vortex_q01/datafusion:parquet	4504808	4585156	0.98

duckdb / vortex-file-compressed (0.973x ➖, 0↑ 0↓)

name	PR 562cc93 (ns)	base c5e075a (ns)	ratio (PR/base)
vortex_q00/duckdb:vortex-file-compressed	9773956	9919645	0.99
vortex_q01/duckdb:vortex-file-compressed	5650353	5876722	0.96

duckdb / parquet (1.010x ➖, 0↑ 0↓)

name	PR 562cc93 (ns)	base c5e075a (ns)	ratio (PR/base)
vortex_q00/duckdb:parquet	23246140	23121933	1.01
vortex_q01/duckdb:parquet	9439667	9295209	1.02

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No file size changes detected.