Ad Click Aggregation

An ad click aggregation system counts billions of ad clicks per day, per ad and per minute, for real-time dashboards and for billing advertisers. Because the numbers become invoices, the design must handle duplicates, late events, and failures without over- or under-counting.

Clarify requirements

Functional

• Ingest click events: click_id, ad_id, campaign_id, user_id, ts, ip, country, device.
• Query click counts per ad (and campaign) over the last M minutes, aggregated per minute.
• Top-N most clicked ads in the last M minutes, filterable by country/device.
• Feed billing with accurate daily totals.
• Out of scope: impression tracking (same pipeline pattern), fraud ML models (integrate as a filter).

Non-functional

• 10B clicks/day; peak 5x average.
• Dashboard freshness within ~1 minute.
• Billing accuracy: exactly-once counting (no double counting, no loss); final totals reconciled.
• Handle late events (mobile clients offline) up to some bound.
• Fault tolerant, horizontally scalable.