Mid-LevelPerformance & Load Testing
How do you establish performance baselines and SLAs?
- baselines
- SLAs
- performance metrics
Answer it first, then compare. Nothing here is saved or scored.
Model answer
Steps: (1) Run baseline tests against the current system under typical load. (2) Measure key metrics: response time (p50, p95, p99), throughput (requests/sec), error rate, resource utilization. (3) Correlate with real user monitoring (RUM) data if available. (4) Define SLAs based on business requirements and user expectations (e.g., page load under 2s, API response under 200ms p95). (5) Store baselines in version control and compare on every release. (6) Set alerting thresholds at 80% of SLA to catch degradation before users notice.
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.