36 lines
1.6 KiB
Markdown
36 lines
1.6 KiB
Markdown
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# People tab — grouped COUNT (vs full faces scan with embeddings)
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`PeopleService::list_people` (GET `/api/people`, fetched on every People-tab
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mount) called `faces_for_user`, which SELECTs every face row for the caller —
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each carrying a 2,048-byte embedding BYTEA that gets decoded into a fresh
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`Vec<f32>` — only to (a) count faces per person and (b) resolve a handful of
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cover faces to file ids. A 10k-face library moved ~21 MB of embeddings per
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request. `merge()` had the same over-fetch plus one UPDATE per face.
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Changes (`FaceRepository` + `PeopleService`):
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- `person_face_stats`: `SELECT person_id, COUNT(*) … GROUP BY person_id`.
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- `file_ids_for_faces`: one `id = ANY($1)` over just the cover face ids.
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- `reassign_person_faces`: merge as ONE set-based UPDATE (was: load all
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faces, filter in Rust, one UPDATE per face).
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## Reproduce
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```bash
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cargo run --release --features bench --example bench_people_list
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# tunables: BENCH_FACES=10000 BENCH_PERSONS=20 BENCH_REPS=5
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```
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## Results (4 cores, local PG16, 10,000 faces / 20 persons)
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| mode | total ms | bytes moved |
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|--------------------------|---------:|------------:|
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| BEFORE — full face rows | 30.40 | 20,960,000 |
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| AFTER — COUNT + covers | 3.76 | 1,280 |
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- **8.1× faster** and **~16,000× fewer bytes** off the wire per People-tab
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mount. The heap never materialises 10k embedding `Vec<f32>`s.
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- The BEFORE row also allocated ~21 MB per request on the server; under a
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handful of concurrent mounts that was tens of MB of transient RSS for a
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page that shows 20 avatars.
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