Scatter-Gather Aggregator - Senior¶
Fan-out amplifies tail latency, retries, connections, and failures.
| Control | Benefit | Cost |
|---|---|---|
| global deadline | bounded latency | partial answers |
| hedged request | lower tail | extra backend load |
| concurrency cap | protects dependencies | queueing |
quorum k-of-n | tolerates failures | weaker completeness |
| per-shard circuit breaker | isolates bad shard | stale or missing data |
Monitor branch p99, aggregate p99, completion ratio, canceled work, hedge rate, and connection use. Test correlated slowness; independent-failure math is misleading when shards share a network or storage tier.
Test yourself¶
- When does hedging make an outage worse?
- What contract describes partial results?
- Why are correlated failures important?
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