System design notifications
Push, email, in-app notifications
Ingest → fan-out → providers. Templates, user prefs, and provider failure.
Week 5Saturday 3 OctoberNotifications
Day 29: Notification service
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System design notifications
Priority, batching, quiet hours
Idempotency keys, digest vs realtime, and how you drop or delay.
Estimation
1B pushes/day, p99 < 5s
Peak QPS, queue depth, worker count, and provider quotas.
Coding design
Design Hit Counter
LC 362. 5-minute window. Binary search on timestamps or buckets.