Serve hourly, daily, and weekly active-user metrics that refresh every hour
From InterviewQuery Stripe DE interview page. Design a pipeline that computes and serves hourly active users (HAU), daily active users (DAU), and weekly active users (WAU) with hourly refresh cadence. Involves pre-aggregation strategy: materialized views or periodic rollup tables at different time grains, incremental computation to avoid reprocessing full windows, serving layer with low-latency reads. Trade-offs between storage cost of pre-aggregated tables vs. query-time computation.