System design interview questionHardAnalytics / Ads
Design an Ad Click Aggregator
Design an ad click aggregator: ingest huge click streams, aggregate counts, and serve campaign stats.
Interview scope
Client → Gateway/LB → App → Message Queue; workers aggregate to DB (+ Cache for hot stats). No Client → Queue/DB.
Functional requirements
- Accept click events from many clients/edges.
- Aggregate clicks per ad/campaign.
- Query recent totals for dashboards.
Scale and quality goals
- Extremely write-heavy — buffer with a queue.
- Don’t update a single SQL row per click synchronously forever.
- Hot aggregates can live in cache; durable totals in DB/object tiers.
Capacity assumption
Design for this scale
Assume ~1B clicks/day (~12k events/s average); peaks much higher during big campaigns.
Practice more than a diagram
Place components on the Froquiz canvas, connect the data flow, and see which decisions the scenario-specific review finds missing. The full exercise and review unlock with Premium.
Explore Premium →