Test Types
Can you differentiate between load, stress, soak (endurance), spike, volume, and scalability testing, and explain when you would use each type?
Explain scalability testing and why it is important.
Explain spike testing and when you would use it.
What is a breakpoint or capacity test, and how do you conduct one to find a system's limit?
What is a smoke or shakeout test in performance testing, and how does it differ from a full load test?
What is configuration performance testing and when is it useful?
What is failover or recovery performance testing, and why would you run it?
What is the difference between backend and frontend performance testing?
What is the difference between scalability testing and load testing?
What is volume testing and when would you use it?
When a system is stressed beyond its capacity, what does 'graceful degradation' mean and why does it matter in a stress test?
Why is a soak/endurance test particularly effective at exposing memory leaks and resource exhaustion?
Workload Modeling
Differentiate between open and closed workload models (arrival-rate vs. fixed VUs) and explain when to use each.
How do you avoid cache skew and unrealistic cache hit rates when designing test data?
How do you create a realistic workload model for a load test, including identifying key user journeys and traffic mix?
How do you derive workload statistics such as target throughput and user behavior patterns from production data like logs and analytics?
How would you leverage load testing and stress testing to ensure a website and app function optimally?
What is the peak-to-average ratio and how does it influence your workload target?
What is the purpose of think time and pacing in a load test script?
What is the role of parameterized tests, and how do you handle unique test data and dynamic values (e.g., session tokens, CSRF) during a load test?
What is workload modeling, and why is it a critical step in performance testing?
When would you run a single-scenario test versus a multi-scenario mixed-workload test?
Bottleneck Analysis & Tuning
Explain Little's Law and how it can be applied in performance testing analysis.
Explain the USE method (Utilization, Saturation, Errors) for monitoring system performance during a load test.
How do connection-pool and thread-pool saturation show up in load test metrics?
How do you correlate client-side metrics with server-side metrics to find a bottleneck?
How do you handle performance bottlenecks once they have been identified?
How do you identify performance bottlenecks from load test results, and what common classes of bottlenecks do you look for?
How would you approach debugging a microservice timing out under heavy load due to database calls?
What are a correlate graph and an overlay graph used for in performance analysis?
What do you mean by profiling in the context of performance testing?
What does the Universal Scalability Law (or Amdahl's law) tell us about how systems scale, at a conceptual level?
What is performance tuning and what are its types (hardware vs software)?
Metrics & Measurement
Explain the concepts of throughput and latency, and why they matter in performance engineering.
Explain the role of response time in performance testing.
How do you define and measure response time and transaction time in load testing?
What do the terms TPS, RPS, and requests-per-second mean, and how are they measured?
What is the purpose of monitoring system resources (CPU, memory, disk I/O, network I/O) during load testing?
What is the significance of analyzing error rates in load testing?
What key client-side and server-side performance metrics do you typically define for load testing, and why are they important?
Load Generation Architecture
Explain the controller/worker (master-slave) model used in distributed load generation.
How do you distinguish between a true system limit and a load-generator limit?
What are the conceptual components of a load testing tool?
What are the pros and cons of running containerized load generators?
What are the trade-offs between protocol-level and browser-level (real-browser) load testing?
What is distributed load generation and why is it necessary?
When scaling load generation, how do you determine the optimal number of virtual users or nodes, and how do you ensure the load generator itself is not the bottleneck?
Why and when would you run load generators from multiple geographic regions?
Why has manual load testing been discontinued?
Lifecycle & Ci Cd Integration
Explain the process of performance regression triage.
Explain the role of performance testing in CI/CD pipelines.
Explain the typical process or lifecycle for conducting performance/load testing.
How do you approach performance testing for a new application or service?
How do you perform regression testing in load testing to prevent performance degradations?
What are the advantages of automated performance testing?
What is continuous performance testing (performance-as-code), and what does it involve as a practice?
When and where in the SDLC should performance testing be integrated, and what is shift-left performance testing and its benefits?
Test Environment & Data
Explain the role of test data management in performance testing.
How do warm-up effects such as JIT compilation, cold caches, and connection-pool warm-up affect load test results?
How do you extrapolate results from a scaled-down test environment to production, and what are the risks?
How do you handle authentication and session management in load testing scripts?
How do you handle performance testing for applications that involve third-party integrations or APIs, and what considerations should you keep in mind?
How do you simulate different network conditions (e.g., high latency, packet loss) in a load test?
What are the risks and careful considerations of running load tests in production?
What is the observer effect in performance testing, and how do you minimize it?
Why should a load test environment mirror production, and what are the caveats if it's scaled down?
Percentiles & Latency Analysis
How are percentiles typically calculated in performance testing reports?
How do you interpret tail latencies like p99.9, and why can they be more important than p95?
How do you read a response-time distribution to understand system behavior under load?
How would you correct or account for coordinated omission when reporting latency?
What is 'coordinated omission' in load testing, and why is it important to understand?
What is the 'knee' or saturation point on a throughput-vs-load curve, and how do you identify it?
What is the relationship between latency and throughput as load increases?
When might percentile-based analysis not apply or be insufficient for evaluating performance?
Why do percentiles matter more than average response time in performance testing, and what do they represent in terms of user experience?
Capacity Planning & Scaling
How can load tests be used to validate autoscaling behavior and rate limits?
How do load testing results inform capacity planning?
How do you plan capacity and de-risk a new product launch with uncertain demand using load testing?
What are the trade-offs between cost and performance in the context of load testing and infrastructure?
What does 'headroom' mean in capacity planning, and how do you decide how much to provision?
Virtual Users & Test Criteria
How do you define performance acceptance criteria or thresholds for a load test?
What are Non-Functional Requirements (NFRs) and how do they guide your load test design?
What are the four golden signals, and how do they apply when analyzing a load test?
What are virtual users in performance testing?
What do the terms 'virtual user' and 'concurrent users' mean, and how can you estimate the required number of virtual users for a test?
What is concurrent user load in performance testing?
What is the difference between a check/assertion and a threshold in a load test, and how do thresholds gate a build?
What is the purpose of ramp-up, ramp-down, and steady-state phases in a load test?
Best Practices & Reproducibility
How do you ensure reproducibility in performance testing?
How do you report and communicate load test results to non-technical stakeholders?
What are the common challenges encountered in load testing?
What are the key best practices you follow to get trustworthy load test results?
What is a baseline run, and why is establishing a baseline important before further testing?
Why is it important to change only one variable at a time between load test runs?
Fundamentals & Purpose
How does performance testing impact user experience?
How is performance testing different from functional testing?
What are the potential consequences or costs of not performing load testing before a release?
What do you understand about performance testing and load testing, and how do they differ?
What is performance testing and why is it important in software development?
What is the difference between functional and non-functional testing?
Why is load testing important in software development, and what are its key goals?
Why is software testing required?
Tooling & Cloud
What are the benefits and drawbacks of SaaS/cloud load-testing services versus self-hosted tools?
What are the benefits of cloud-based performance testing?
What are the trade-offs between GUI-based, scripting-based, and code-as-tests load testing tools?
What factors do you consider when choosing a load-testing tool for a project?