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