perf(pragmastat): more perf tweaks#3595
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Pre-compute ln() arrays once per column before the two-sample pair loop, eliminating redundant O(n) log passes (k=10 cols: 10 passes vs 90). Add indexed parallel CSV reading for large files (>=10k rows) using ThreadPool + crossbeam_channel, following the moarstats.rs pattern. Falls back to sequential reading for stdin or small files. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
…rrors Chunks from parallel CSV reading were merged in arrival order rather than chunk index order, which could scramble row ordering. Now sends chunk_idx with results and sorts before merging. Also propagates an error instead of silently returning empty data when the index fails to open. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Pull request overview
Improves qsv pragmastat performance by adding an indexed, multi-threaded CSV read path for large inputs and reducing repeated log-transform work during two-sample ratio calculations.
Changes:
- Add an indexed + chunked parallel CSV ingestion path for large files.
- Precompute per-column log-transformed values once and reuse them across two-sample pairs.
- Refactor two-sample computation to accept optional precomputed log slices.
Propagate the --no-headers flag to per-chunk Config in the parallel CSV reading path, fixing incorrect seek positions when headers are disabled. Add two integration tests exercising the parallel path (>=10k rows): pragmastat_parallel_reading and pragmastat_parallel_reading_no_headers. Addresses Copilot review feedback on PR #3595. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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