Incremental extraction with deletes
Design an incremental extraction system that syncs ~200 large source Postgres/MySQL tables into a warehouse hourly, where full re-extracts are too slow/expensive. The naive approach polls 'rows where updated_at > last_watermark', but it misses hard deletes (rows that vanish), misses rows updated within the same second as the watermark, and double-counts when clocks skew. Design an incremental extract that captures inserts, updates, AND deletes correctly and is safe to re-run after a failure.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.