[PR] fix(parquet): clear round-trip benchmark buffer each iteration [arrow-rs]

["sdf-jkl (via GitHub)" <gi...@apache.org>]

sdf-jkl opened a new pull request, #11298:
URL: https://github.com/apache/arrow-rs/pull/11298

   # Which issue does this PR close?
   
   N/A — small benchmark correction.
   
   # Rationale for this change
   
   `parquet_round_trip` clears its output buffer outside `b.iter`, so successive timed calls append complete files to the same Vec. Memory usage grows with Criterion's iteration count, and reallocations can affect the measurement. The subsequent read benchmark also inherits the accumulated bytes.
   
   # What changes are included in this PR?
   
   Move `buffer.clear()` inside the timed closure. Each iteration writes one file while retaining buffer capacity; the read benchmark receives the final single file. No library behavior changes.
   
   # Are these changes tested?
   
   - All 92 cases in the patched `parquet_round_trip` executable passed Criterion's `--test` smoke mode.
   - `rustfmt --check` and `git diff --check` passed.
   - Compared the actual benchmark executable at base `8208506f8f9ec193c08023ac2477d211d1d86d20` and this patch, using the same lockfile/dependencies. Linux x86-64, Ryzen AI 9 HX PRO 470, Rust 1.91.1, Criterion 0.8.2, optimized bench profile, pinned to CPU 2. Ran before / after / after / before, with 0.5 s warmup, 2 s measurement, 20 samples and 10,000 bootstrap resamples per case.
   
   | Benchmark | Before (ms, runs 1 / 2) | After (ms, runs 1 / 2) | Change in mean |
   | --- | ---: | ---: | ---: |
   | `write String(20) plain` | 4.548 / 4.496 | 4.382 / 4.340 | -3.6% |
   | `write int32 dict` | 6.902 / 7.092 | 6.859 / 7.009 | -0.9% |
   | `write int32 plain` | 2.991 / 3.033 | 2.773 / 2.761 | -8.1% |
   | `read String(20) plain` | 2.276 / 2.267 | 2.308 / 2.333 | +2.2% |
   | `read int32 dict` | 1.011 / 1.068 | 1.005 / 0.991 | -4.0% |
   | `read int32 plain` | 0.529 / 0.527 | 0.516 / 0.506 | -3.1% |
   
   Peak RSS for the whole filtered benchmark process was **602.3 / 601.7 MiB before**, versus **84.8 / 84.6 MiB after** (`/usr/bin/time -v`). This includes fixture generation and the harness, not just the timed operation.
   
   These short local runs quantify the changed benchmark behavior, not a Parquet implementation speedup. Plain integer writes improved by about 8%; dictionary-write timings were close. Read results varied in both directions, including a 2.2% increase for the string case.
   
   Measurement arguments (same on both revisions):
   
   ```sh
   cargo bench -p parquet --bench parquet_round_trip -- \
     --warm-up-time 0.5 --measurement-time 2 --sample-size 20 \
     --nresamples 10000 --noplot \
     '^(write|read) (int32 (dict|plain)|String\(20\) plain)$'
   ```
   
   # Are there any user-facing changes?
   
   None; benchmark harness only.
   


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Re: [PR] fix(parquet): clear round-trip benchmark buffer each iteration [arrow-rs]

["Jefffrey (via GitHub)" <gi...@apache.org>]

Jefffrey commented on PR #11298:
URL: https://github.com/apache/arrow-rs/pull/11298#issuecomment-5906989720

   thanks @sdf-jkl & @etseidl 


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Re: [PR] fix(parquet): clear round-trip benchmark buffer each iteration [arrow-rs]

["Jefffrey (via GitHub)" <gi...@apache.org>]

Jefffrey merged PR #11298:
URL: https://github.com/apache/arrow-rs/pull/11298


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