Design an Ad Click Aggregation & Counting System

An Ad Click Aggregation and Counting System ingests, deduplicates, aggregates, and stores billions of real-time ad impression and click events to power advertiser dashboards, compute Click-Through Rates (CTR), and enforce real-time budget capping.

Functional Requirements

1. Real-Time Click & Impression Counting: Ingest and aggregate raw ad click and impression events in real time.
2. Multi-Dimensional Querying: Support interactive analytical queries by advertisers:
   • "Show total clicks, CTR, and spend for Campaign 8812 grouped by country and device over the past 30 days."
3. Click Deduplication & Anti-Fraud: Detect and drop duplicate clicks (e.g. rapid double-clicks within 1 second) and malicious bot fraud.
4. Real-Time Budget Capping: Automatically pause an ad campaign within < 10 seconds when the advertiser's daily spend budget is exhausted.

Non-Functional Requirements

• Massive Ingestion Throughput: Ingest > 500,000 click events/second and 5,000,000 impressions/second.
• Exactly-Once Processing Guarantees: Ensure no click event is double-counted or lost for advertiser billing accuracy.
• Sub-Second Analytical Queries: Advertiser dashboard queries must execute in < 500 ms.