57 lines
2.4 KiB
Markdown
57 lines
2.4 KiB
Markdown
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# Static assets & API responses — precompressed siblings + explicit Brotli level
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Two related findings, one root cause: tower-http's `CompressionLayer` default
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maps to **Brotli QUALITY 11** (`async-compression Level::Default` →
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`BrotliEncoderParams::default()`, brotli-8.0.2 `encode.rs:323` — verified in
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source and empirically below). Quality 11 is a deploy-time setting; it was
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running per request on:
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- every SPA asset (`interfaces/web/mod.rs` layer): ~1.3 s CPU per 700 KiB
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bundle per request;
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- every compressible API response (`main.rs` global layer): ~90 ms CPU per
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64 KiB JSON response.
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Changes:
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1. **Precompressed statics.** `frontend/scripts/precompress.mjs` (build step,
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node:zlib only) emits `.br`/`.gz` siblings for text assets; `ServeDir` now
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uses `precompressed_br()/precompressed_gzip()` — a request costs a file
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read, and clients get the *better* q11 bytes, paid once per deploy
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(~1.4 s for the whole bundle).
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2. **Explicit level 4** on both `CompressionLayer`s
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(`CompressionLevel::Precise(4)`) — the on-the-fly fallback for statics
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without siblings, and the global API layer.
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## Reproduce
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```bash
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cargo run --release --features bench --example bench_static_precompress
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# tunables: BENCH_ASSET_KB=700 BENCH_REPS=30
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```
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## Results (4 cores, this container)
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**Per-request cost, 700 KiB JS-like asset (94 % compressible):**
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| mode | ms/request | speedup |
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|-----------------------------|-----------:|--------:|
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| BEFORE — on-the-fly Brotli | 1,324.31 | 1.0× |
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| AFTER — precompressed read | 0.657 | **2016×** |
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**Brotli level sweep, 64 KiB JSON-like API response:**
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| level | ms/resp | out KiB |
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|-------------------------|--------:|--------:|
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| Default (= quality 11!) | 90.10 | 5.4 |
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| **Precise(4)** (chosen) | 0.91 | 6.2 |
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| Fastest | 0.15 | 9.3 |
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- Statics: 3 orders of magnitude less CPU per request, while shipping
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*smaller* bytes than the runtime default would at any reasonable level.
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- API responses: **99× less CPU** for ~15 % more bytes (5.4 → 6.2 KiB) —
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`Precise(4)` is the classic dynamic-content operating point; `Fastest`
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gives up too much density (9.3 KiB).
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- Historical note: an earlier review round REFUTED the "default is q11"
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claim twice; the source line and the 90 ms/64 KiB measurement above settle
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it the other way. Measure before believing — in both directions.
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