I had system design round in which I probably did badly.

Question:

Design a system for aggregation of advertisement click events for Facebook Ads.

• Assume events are already in a Distributed message queue.
• Design at facebook scale.
• Query can come for number of click events for particular Ad in last N sec. Design for as much granularity (max 1 min).
• Events can come out of order and there can be outliers who arrive later than expected.
• Requirement to view both real time and archival information.
• How will you store the aggregated results for efficient querying ?

Can you please help as to how this question should be approached. Would appreciate a detailed answer.