Mid-LevelPerformance & Load Testing
How do you set performance testing thresholds and SLAs?
- SLAs
- thresholds
- performance budgets
Answer it first, then compare. Nothing here is saved or scored.
Model answer
Base thresholds on: (1) Business requirements, "checkout must complete in under 3 seconds." (2) Current baseline - measure existing performance, set thresholds to detect regressions (e.g., p95 must not exceed 1.2x baseline). (3) Industry standards - Google recommends <200ms for API calls, <3s for page loads. (4) User expectations - correlated with bounce rates. Express as: p95 response time < X ms, error rate < Y%, throughput > Z rps. Fail the build in CI if thresholds are breached.
What interviewers listen for
- Workload modellingYou design the load shape from product traffic, not from tool defaults.
- Percentile literacyYou read p50/p95/p99 separately and explain why each matters.
- Bottleneck triageYou correlate metrics across application, database, and infrastructure layers.
- Capacity instinctsYou can translate a soak test into a sizing or scaling recommendation.