6 Common System Design Interview Questions (With Example Answers)
An interview for a system designer position is an opportunity to discuss your experience and abilities and to showcase your skills at creating complex systems. You can prepare for your job interview by studying basic design principles and preparing answers to possible questions about them. In this article, we review common questions and answers for a system design interview to help you prepare.
What is a system design interview?
A system design interview is conducted to allow candidates—like programmers, designers, developers and software engineers—sufficient opportunity to prove expertise in the field through the tangible application of knowledge to solve a real problem that a company might be facing.
The system design interview is typically conducted later in the interview process. It is a trial intended to see how well you work on a team and your approach to problem solving using open-ended questions to arrive at the best possible solutions. A system design interview analyzes your process in solving problems and creating designing systems to help clients. It is an opportunity for you to show the hiring manager and potential team that you are a valuable asset and display your skills and expertise in a concrete way.
System design interview questions and answers
System design questions are typically ambiguous to allow you the opportunity to demonstrate your qualifications. You can ask questions before you respond to help you narrow the scope, give you direction and clarify any expectations.
Here are six common questions you may be asked during your system design interview:
1. How would you design a tinyURL system?
A tinyURL is an URL service that allows users to enter a long URL, and then it returns a shorter, unique URL. A hiring manager might ask this to allow you the opportunity to show your solid foundation in design. You can focus on other basics not listed in the example response, like how you create a unique ID for each URL, how you handle redirects and how you delete expired URLs.
Example: "When I was working for a public instant messaging site, I was charged with creating a simple system where every message was limited to 140 characters. It also necessitated shortened URLs of about 30 characters. This tinyURL system is also useful when entering hyperlinks in e-mails or on a smartphone, where there is room for error. TinyURL is a perfect example of the hashtag table. This data structure associates keys with values and is a simple connections code. By using this basic 16-bit hash table, I was able to optimize usability and meet the needs of the system."
2. How would you design a search engine?
Sometimes search engines are needed within a specific department of a company to systematically locate an item or important employee information. Hiring managers want to see that you can tailor designs to the needs of the company. You can detail some of the overall architecture and explain it, using the foundation below. You can also consider discussing any other relevant issues such as website front-end performance, testing search engine improvements and integrating previous search data and trends in indexing.
Example: "Before I relocated here, I was working on a project similar to this one. The search engine I had been enlisted to create needed to work with keyword searches. I began by building an indexer, which is a piece of software that crawls and produces results in a data structure. The crawler would put web page links together and group them or dump them into sets. Then the indexer ran as part of a reduce job to single things out. For each website, the number of links was calculated and analyzed for presentation. I had the crawl set for H1 and H2, rather than H3s. Then I checked outbound links to avoid spammers. Lastly, I checked the serving results to verify that the design was working at optimal capacity and relevancy."
3. How do you design a web crawler, and when should it be used?
A crawler is a program designed to visit other sites and read them for information. This information is then used to create entries for a search engine index. It is typically called a 'bot" or "spider." Be certain to show within your explanation that you know the intricacies of web crawling.
Example: "Although crawling the web is a challenging task, I have managed to build one for a previous project. The crawler scrapes data from a specific sector, in this case, the fashion industry. I needed to integrate a URL dispatcher, which is a server whose responsibility is to distribute seed URL to a multitude of servers. Next, the crawl supervisor passed the URL to bots using the designed messaging queue. The spider, the basis for any crawler, extracted the data from the web page and loaded it into my file system. Next, the extract, transform and load (ETL) cleaned up the content and reformatted it to store it into the database. In such a way, I was able to crawl the web looking for and organizing the information needed."
4. How do you design a shared drive?
Hiring managers ask this to explore algorithm basics and backgrounds. Before you begin, make sure you understand the purpose of the task. Knowing if the changes will be registered in real time, if locking will be necessary and if it needs to be naturally convergent will help you give a complete answer.
Example: "This system works on differential synchronization. It is keeping two or more copies of the same document synchronized with each other in real time, so if a change is made on one version, the same alteration happens on all the others. It is a complex challenge, but differential synchronization is scalable and fault tolerant. The three common approaches are ownership, event passing and three way merges. I last had to do this to support in-house document sharing for one of our clients. They wanted real-time collaboration, so three-way merging was not a good option since changes are lost and cannot take effect, as major collisions are common. I used event-passing to allow for real-time collaboration as the locking or ownership approach would only allow the first one opening the document to make any adjustment. This served our client well, as its employees were able to work collaboratively even when out of office or on different schedules."
5. What is required to design a garbage collection system?
Garbage collection ensures a Java system is running appropriately and frees a programmer from having to do it manually. Hiring managers look to see if you know how to truly design the ins and outs of various systems. A GC makes systems memory efficient.
Example: "One of my recent clients needed a way to have more memory, but there was an issue with always having to go in and deal with memory deallocation. The nature behind garbage collection is to make a system appear as if it has a seemingly endless amount of memory. What is really happening is that the system is re-purposing the memory. When a system is running slowly, a garbage collector goes in and collects what is no longer being used. I set up their system so that if an object is referenced or recursive in nature, it remains. Next, it goes through methodically and marks whatever has not been referenced and sweeps only that. Using the mark and sweep method with the void command helps to repurpose and open up memory no longer being used. With this in place, my client had a faster system with less maintenance required."
6. How do you design a recommendation system?
Recommendation systems help users find what they want more efficiently. They help clients and customers by offering alternatives and allowing for choice. Hiring managers inquire about this to see if you are able to create systems that are user-friendly and focused.
Example: "One of my first and most loyal clients had a problem where their customers were struggling to find options on their website. Their search had to be exact in order to find the product. I suggested we implement a recommendation system to help with customer satisfaction and possibly sales. Using the most prominent approach of collaborative filtering, I designed the system to weave a sort of information tapestry to give our client's customers suggestions based on user similarity. The system became more user-friendly and produced a 10% increase in sales for my client."
System design interview tips
As you consider your own responses to the standard system design interview questions above, try using the following tips to help you feel more confident and prepared for your interview:
Use the STAR response technique
Formatting your responses using the STAR interview response technique is a strategy to help you craft answers that illustrate your knowledge and qualifications through specific experiences. STAR is an acronym for Situation, Task, Action and Result. Using the STAR method, discuss an applicable situation, identify the task you needed to complete, outline the actions you took and reveal the results of your efforts to demonstrate your skills to the interviewer.
Understand the goals
Ask clarifying questions to help you understand who the users will be, what they need and what the inputs and outputs of the system will be. Inquiring about these basics will help your focus and show your product sensibility and teamwork.
Use your background as an advantage
You bring a unique set of values and knowledge that no one else can. Rather than trying to cater to what you think is wanted, exhibit your own expertise and show you are valuable and irreplaceable because of your skills and ability.
Practice is essential
The opportunity to go through the design interview process over and over again while applying these tips will help you project confidence, and the familiarity you have with the topic will reveal your qualifications. Spend time practicing interview question answers with a friend, family member or in front of a mirror.
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