Step 1 of 11 · Intro

Design ad click aggregation

Count billions of clicks per window, exactly once, even when events arrive late.

How it works

• ›Ingest: accept a click quickly and acknowledge it.
• ›Count: group clicks into time windows per campaign.
• ›Query: advertisers read counts over time, mostly recent ones.

What you'll build

1. The API and the data model
2. A stream-and-workers pipeline into a time-series store
3. A dedup guard in front of the stream
4. A fleet that survives a lost worker or broker
5. Reasoning about late events, exact vs approximate counts and hot keys