Proximity Service — Notes

Functional

• Nearby query: list places within radius / k-NN of point.
• Bounding box query.
• Optional autocomplete with location bias.

Non-functional

• p99 < 200 ms.
• Read-heavy.
• 99.99% availability.

Capacity

• 100M+ POIs globally.
• Millions of queries/s peak.

Schema

• places(id, name, lat, lng, cell_id_S2, category)
• cell_index(cell_id → place_id list) materialized for fast fetch.

Trade-offs

• Static fence vs dynamic boundary: store cell IDs at multiple zoom levels for flexible queries.
• Precompute hot cells (city centers) into cache for instant response.
• Geohash vs S2 vs H3: pick one and stick; cross-system conversion is painful.

Refs

• "S2 Geometry Library" docs.
• Uber H3 hex grid docs.
• ByteByteGo "Design proximity service".
• Alex Xu Vol 2.