# A streaming aggregation tumbles in 5-minute event-time windows with bounded out-of-orderness waterma Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem A streaming aggregation tumbles in 5-minute event-time windows with bounded out-of-orderness watermark using 60-second lag. The product team needs to catch slightly-late events (mobile retries up to an hour) but cannot hold engine state forever. The section's worked configuration is allowed lateness of 60 minutes plus a dead-letter destination for events past the budget; events on time fire once, slightly late events fire again with updated totals, very late events route to the dead-letter sink for the next-day reconciliation pass. Walk the timeline by adding two pieces to the canvas: an annotation on the aggregation transform stating the allowed-lateness budget, and a dead-letter storage destination wired from the aggregation for events past the budget. ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/a-streaming-aggregation-tumbles-in-5-minute-event-time-windo-94806a5a) - [System Design Interview Questions](https://datadriven.io/data-engineering-system-design) - [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep) - [Daily Challenge](https://datadriven.io/daily) --- Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.