HLD-228·Geo & Telemetry
Medium · 1,000 ptsLive "Nearby Friends" Geohash Proximity Radar
Design Snap Map / Find My Friends live proximity sharing where mobile clients stream periodic GPS pings and query friends currently within a 5-mile geohash radius.
Max p99
≤ 52 ms
Availability
≥ 99.5%
Budget
≤ $5,500
Functional Requirements
- FR-1POST /location/ping — Updates ephemeral user coordinates in geohash_cell cache and history store.
- FR-2GET /location/nearby/{user_id} — Returns opted-in friends currently inside adjacent geohash cells.
- FR-3DELETE /location/ping/{geohash_cell} — Supports tenant retention TTL expiry, rule updates, or stream cleanup while keeping recent rollup caches fresh.
- FR-4Must handle stadium/festival geohash hotspots and survive storage node crashes.
Workload Profile
Baseline Pings24,000 Radar Read RPS / 12,000 GPS Write RPS
Festival Crowd Surge68,000 Read RPS / 28,000 GPS Write RPS
Active Working Set18 GB ephemeral live coordinates
Traffic DistributionDense spatial hotspot on downtown/venue geohash_cell keys
Consistency Model
Bounded eventual location freshness (< 5s GPS ping lag) acceptable for proximity radar.
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