Mass Messaging: Reaching Millions During Large-Scale Disasters
summary
Facebook builds a Safety Check system that leverages newsfeed sampling and recursive friend fan‑outs to find and notify people in a disaster zone without a prebuilt geo index. It uses lightweight DB flags plus in‑memory TTL locks to avoid duplicate notifications, a server‑driven cross‑platform message model with TTLs and impression counts, and dark‑launch stress tests. The result: the system invites 3 million in under five minutes while scanning over a billion rows and successfully reaching millions.
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chapters (13)
- 0:00Introduction
- 0:27Inspiration
- 3:48Geolocation Query
- 5:32Algorithm
- 6:49Why does it work
- 8:14Race conditions
- 10:26Mass messaging in practice
- 13:38Safety Check
- 15:42Lessons Learned
- 18:42Dynamic Content
- 20:19Caching
- 22:03Stress Testing
- 23:29Conclusion
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