API Design · Senior · Question 17 of 75

What does an API's p99 latency SLO imply for its dependencies?

1Only the average matters
2Dependencies don't affect latency
✓Correct answer: Tail latencies add up across sequential calls; parallelize, set tight timeouts, use hedging or caching for slow dependencies

Explanation

With several downstream calls per request, the slowest one dominates. Fan-out amplifies tail latency.

Further reading

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