Design an Ad Event Aggregator

An Ad Event Aggregator collects high-volume ad events (impressions, clicks, installs), enriches them with metadata, and serves both real-time dashboards and historical analytics queries. The same architecture applies to other high-volume metrics systems, but this walkthrough focuses on ad analytics. With 100M+ events per day, sub-second query latency, and strict data accuracy requirements, this question tests your understanding of stream processing, data enrichment, and OLAP database design.

This walkthrough follows the Interview Framework and focuses on what you'd actually present in a 45-60 minute interview.