6 of the Most Common System Design Interview Questions

By Indeed Editorial Team

Published November 5, 2021

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

System design interviews involve a set of questions aimed at evaluating your knowledge and experience in the field. A system design interview can be your chance to showcase your skills and experience with designing systems like search engines, web crawlers, or shared databases. Preparing for the interview can help to clarify your understanding of your own abilities and to present them confidently to an experienced professional. In the following article, we discuss the six most commonly asked system design interview questions and offer tips and examples to help you prepare for your system design interview.

6 common system design interview questions

Answering system design interview questions is an opportunity for candidates to demonstrate their expertise by providing specific solutions to the company's problems. These interviews typically have open-ended questions that give you the opportunity to show your skills, qualifications, and knowledge. You can ask your own questions to help focus your answers and better understand the needs of the company.

The interviewer may conduct the actual system design interview after you pass the first interview steps. This is a trial intended to test your teamwork skills, your approach to open-ended questions, and your methods for arriving at potential solutions. It's also an opportunity to show the hiring manager and their team that you are a valuable asset to their company. The following are six of the most common system design interview questions that interviewers may ask:

1. How do you design tinyURL systems?

A tinyURL is a service that takes a long, complex URL and turns it into a short, unique URL that is easier to share. The hiring manager may ask this question to assess your design skills. While the focus of the question may be simple, you can also choose to discuss how you might create a unique ID for each URL entered, handle redirects, or delete expired URLs.

Example: "In my previous position, I created a simple system with messages limited to 140 characters in length. This necessitated URLs of around 30 characters. TinyURL is a great example of a hashtag table. The data structure I created associates keys with values, being a simple connections code. By making use of a basic 16-bit hash table, I was able to meet the system's needs."

2. How might you create a search engine?

Companies or organizations typically use search engines to locate files or find important employee information. A hiring manager may want you to show that you understand the company's needs and can customize your design to meet those specific requirements. Other relevant discussion topics that you might wish to discuss include monitoring website front-end performance, testing improvements to the search engine, and integrating prior search data and indexing trends.

Example: "At my last position, I helped create a search engine that worked with keyword searches. I designed and built an indexer—a piece of software that crawls the internet then produces its result in a data structure. The crawler would then group links into sets (in this case, H1s and H2s). I checked the outbound links to avoid any spam and verified that it worked at optimal capacity to give relevant results."

3. How do you design web crawlers?

Crawlers are programs that visit other websites and read through them for information. That information is then used to create an index for a search engine. Crawlers are also referred to as "bots" or "spiders." When crafting your answer, it's important to show that you are familiar with the specific details of web crawling.

Example: "I built a web crawler as part of a previous project to scrap data from a specific sector, such as the cosmetic industry. I also integrated a URL dispatcher, which distributes a seed URL to multiple servers. The crawler would then pass the URL to bots using a designed queue. The spider would extract the data from the page, loading it into my file system. Then, the extract, transform, and load (ETL) would reformat the content for storage in the database."

4. How do you design shared drives?

A hiring manager may ask this question to explore your knowledge of algorithm basics and backgrounds. It's important you discuss whether to design it to register changes in real time, whether to allow locking, and if the shared drive may be naturally convergent. Mentioning these key terms can show that you fully understand the details of shared drive design.

Example: "The system I designed on a prior project works on differential synchronization. If I change one version, the same change occurs in all the others. The three most common approaches to designing shared drives are ownership, event-passing, and three-way merges. I chose event-passing for my system since the client requested for it to allow real-time collaboration."

5. What do garbage collection systems require?

A garbage collection system includes a running Java system, which frees up a programmer from completing that task manually. Garbage collectors make systems highly memory efficient, so it's important to prove that you can design and execute them. A hiring manager may use this question to test whether you are familiar enough with various systems to design yours efficiently.

Example: "The purpose of garbage collection is to give the sense of endless memory. My last client wanted more memory without having to reallocate it frequently, so I designed their system to identify and keep items that are referenced or recursive. The garbage collection system then marks and only sweeps non-referenced items. Making use of a mark and sweep method helped repurpose and open up memory that was no longer being used, giving the client a faster system with fewer maintenance requirements."

6. How might you design a recommendation system?

Recommendation systems help users find information easily and efficiently. These systems suggest alternative choices to customers, allowing the user to choose their favourite from a list of options. Hiring managers often ask questions about recommendation systems to see if you can design a system that is both user-friendly and highly focused.

Example: "A previous client needed to provide options for customers on their website while also having a precise search function. I suggested we use a recommendation system to help improve sales and customer satisfaction. My design used collaborative filtering to organize the information and offer suggestions based on user similarity. The system I created was far more user-friendly than their previous solution and helped increase the client's sales by 15%."

System design interview tips

System design interviewers typically look for demonstrations of technical knowledge with concrete examples from your work history. The following tips can help you succeed in your system design interview:

Use the STAR response technique

Formatting your responses using the STAR (Situation, Task, Action, and Result) technique can help you craft answers using specific work situations to show your knowledge and experience. This method entails choosing an applicable event, identifying the task to complete, outlining the actions to be taken, and revealing the results of your knowledge, skills, and effort to the hiring manager. The STAR technique can be an excellent way to demonstrate your talent and technical skill to hiring managers. Asking questions can help you adjust your answers to meet the company's needs and highlight your soft skills.

Related: How to use the STAR Interview Response Technique

Understand the goals

During your system design interview, it's important to ask any clarifying questions that can help you fully understand what the interviewer is asking. These can include questions about who the users may be, what they might need, or what inputs and outputs the system may require. By asking these basic questions, you can help to focus your responses while showing both your teamwork skills and your product sensibility.

Related: Problem-Solving Interview Questions and How to Answer Them Effectively

Use your background knowledge

Using your specific background knowledge to answer questions can help distinguish you from other applicants. You may have unique skills or expertise that no other applicant has, and demonstrating them to interviewers can prove your value as an employee. Your customized approach may be the best solution to one of the company's problems.

Related: Preparing for a Mock Interview

Practise your answers

Before your interview, it's important to go through the design interview process repeatedly, whether in your head or with a friend or family member. Practising can help you present yourself confidently in interviews and show hiring managers how familiar you are with system design. Familiarity can only come from practice, so it's vital to review possible interview questions before your interview, craft your answers thoughtfully, and be flexible in incorporating new information.

Being adaptable with your answers can help impress your interviewer and show your broad understanding of the field. You can ask clarifying questions and use concrete examples from your earlier work to demonstrate how you would design and implement solutions to the hiring manager's problems.

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