People near me
Your task
Design the 'people near me' feature for a social app with 80M daily actives where users move and the app must surface other online users within an adjustable radius (1–50km), refreshed every ~10s, read-heavy with a ~50:1 read/write ratio. How do you index location, scope the search, and bound staleness?
It covers
- Geohash
- Redis
- Fan out