Tail latency in sharded search
Design tail-latency control for a sharded search system where a single query fans out to 200 shards and the response can only return once every shard replies — so the slowest shard (the straggler) sets the user-visible latency, and at 200 shards p99-per-shard becomes near-certain on every query. The product needs a hard p99 < 150ms even when a few shards are slow (GC pause, hot partition, a degraded node). How do you stop one slow shard from dictating every query's latency, while keeping results good enough?
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 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.