Event sourcing append-only store
Design an append-only event store for an event-sourced system: events are immutable facts grouped into per-aggregate streams, writers append to a stream with an expected-version for optimistic concurrency, and readers replay a stream from the beginning to rebuild state or subscribe to a global feed of new events. Expect millions of streams, ~100K appends/sec, and a guarantee that appends to one stream are strictly ordered. How do you store and serve this?
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.