Top 8 Software Performance Engineering Interview Questions

Top 8 Performance Testing Interview Questions and Answers

Haven’t we all experienced the rising pressure of interviews and the unpredictable questions that are brought up for which we lack the right answers, specifically in the domain of performance testing and the nuances within? But with a handy go-to guide for certain interview questions on performance testing and software performance engineering as a whole, be ready for anything that may come your way.

Herein, we have the top 8 most crucial questions that may be posed during an interview on performance testing services as a whole and detailed answers to those, to further enable you prepare for such interviews, because as much as your hands on work is important, how you articulate what you know is equally important too. 

Q1. What is Performance Testing?

Performance testing is a core software testing service which involves testing an application for any performance bottlenecks.

It becomes a QA effort as well, for checking an application’s performance under varied user-loads. As a non-functional testing effort, performance testing tackles the pain points faced in real time by end users, such as crashing of applications or websites, load time of an application, etc.

There are several other complex facets too to performance testing, but this is a good starting point.

Q2. What are the most commonly used tools for Performance Testing? Name some factors based on which Performance Tools are selected?

Some of the common and popular tools used for performance testing are:

  1. Apache JMeter– As an open-source performance testing tool and a Java application, Apache JMeter helps in load testing of an application by simulating a specific user-load across servers and protocols
  2. LoadRunner– It is a commercial and paid tool for measuring the performance across an array of technologies and protocols, thus an efficient choice for saving time and costs due to flexible scaling-up and down options
  3. WebLOAD– For web and mobile applications, this tool provides support that ranges from test planning, design, execution to analysis for increasing an organization’s scalability 
  4. Silk Performer– As a performance testing tool, Silk Performer helps in conducting load and stress testing as well. With its customized load testing scripts, it produces effective and reliable results by simulating real time user-load
  5. Gatling– As an open-source load testing tool, it helps resolve bottlenecks for web applications early-on via an effective DevOps and CI pipeline

There are an array of performance testing tools which have been trending for a while now. The factors that play a crucial role in choosing certain tools over others can be numerous- to name a few:

  • Performance testing environment;
  • Support extended for protocols;
  • Organizational budget to bear the license cost;
  • Features of the tool vis-à-vis the requirements;
  • Customer support from the vendor; etc.
Q3. What is the need for Performance Testing?

Performance testing is a crucial testing and QA effort for eliminating any performance bottlenecks in an application or a website. Before a product gets released, and even post-release, performance testing helps evaluate users’ pain points- through user monitoring, analysis and effective Application Performance Management as a whole. An application’s robustness is enhanced with the help of effective performance testing to avoid losing out on users’ trust.

Q4. What does Performance Testing comprise of?

Performance testing is an umbrella for certain types of testing with an end goal of designing the right kind of workload. Some of these different testing types are defined as follows:

  • Load testing- It is essentially conducted to check an application’s performance under a particular user-load. There might be times, such as during festive seasons, when the user-load would have an anticipated increase. Load testing thus, helps identify performance fallacies under such anticipated user-load
  • Endurance testing- This type of testing is conducted over an extended period of time to check an application’s sustained performance under a particular user-load
  • Stress testing- Stress testing involves putting excessive load on an application till the breaking point of the system to check its performance under high user-load
  • Spike testing- This is conducted to check an application’s performance for a spiked user-load
  • Scalability testing- This is another type of performance testing for measuring the application’s performance for scaling-up to handle a spiked user-load
  • Volume testing- This is essentially done to monitor the performance of an application when there is an increase in the data
  • Failover testing- This testing type is an important facet for verifying a system’s ability to handle extra load amidst a system failure
Q5. What are the common performance bottlenecks? Giving a realistic example, explain how have you overcome and tuned it?

Performance bottlenecks are essentially those pain points that hamper an application’s performance. Some of the common performance bottlenecks include-

  • Memory Utilization- This bottleneck often arises when the system runs out of memory or has insufficient memory in its RAM, among other causes, leading to slower performance of the system as a whole. The CPU does not receive adequate information as there exists truncated memory and space, resulting in dilapidating speed of functions
  • CPU Utilization- A most common performance bottleneck is that of CPU Utilization. This occurs when the CPU might be strained due to overwhelming data inputs. As aforementioned, due to less memory as well, the processing power of the CPU might get dwindled
  • Network Constraints- More often than not, one faces this bottleneck when there is insufficient network bandwidth for effective communication. This again, can occur due to slow processing power or outdated network hardware

Other performance bottlenecks also include any limitations within the software itself or its disk usage. 

A realistic example of how a memory bottleneck can be tuned is by effectively monitoring the leaks and optimizing cache memory to enhance an application’s performance.

Q6. How do you differentiate between Performance Engineering and Performance Testing?

Performance testing essentially is a testing effort to identify all possible performance bottlenecks in a software product which may or may not have conclusive solutions but is a technique to help eliminate those bottlenecks. It is conducted to measure an application or website for stability, speed, scalability, etc.

Within performance testing, different types of testing can be conducted such as load testing, endurance testing, stress testing, etc. With effective performance testing services, bottlenecks can be easily eliminated.

On the other hand, performance engineering is an effort conducted from the very beginning of a product’s lifecycle to ensure that the product will be capable of sustaining an extra load in the end. From the planning stage to its execution and release, performance engineering helps attain a consistent check on bottlenecks throughout.

Be it the UI/UX of an application or the practices to stay at par with the latest in industry, performance engineering helps enhance and optimize performance standards of the product. Performance engineering also helps in “shifting left” in the cycle, i.e., to identify and eliminate any bottlenecks early-on to reduce remediation efforts post-release.

Q7. How do you design your workload model?

A workload model defines the strategy of dispersed user-load across an application at a specific point of time. It is essentially designed to understand and examine the different types of load and activities that users perform in the same application or website.

To design an effective workload model, the requisite starts from analyzing the production data and usage. This signifies the rate at which users are coming in. For example, with Google Analytics, historical data usage can be examined, wherein one can pick the transactions that users have utilized more or the nuances involved during peak duration, etc. 

Q8. What is Little’s Law?

Developed by John Little in 1954, Little’s Law revolves around the queuing system- when applied to the domain of performance testing, the equation for the same is-


This is essentially used to calculate the number of users by multiplying the transactions per second with the sum of execution time, think time within a script and pacing time between iterations. A workload model can be effectively defined using Little’s Law.

Thus, with these questions, prepare well for even the most challenging performance testing interviews so you can articulate your experience in the most effective manner. For more inputs, read our blogs on performance testing and our exquisite hands-on experience and offerings on performance testing services. Good luck!

About the Author

QA InfoTech

QA InfoTech

Established in 2003, with less than five testing experts, QA InfoTech has grown leaps and bounds with three QA Centers of Excellence globally; two of which are located in the hub of IT activity in India, Noida, and the other, our affiliate QA InfoTech Inc Michigan USA. In 2010 and 2011, QA InfoTech has been ranked in the top 100 places to work for in India.

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