Scalability In System Design
Scalability refers to the ability of the System to cope up with the increasing load. While designing the system you should keep in mind the load experienced by it. Its said that if you have to design a system for load X then you should plan to design it for 10X and Test it for 100X. There can be a situation where your system can experience an increasing load. Suppose you are designing an E-commerce application then you can expect a spike in the load during a Flash Sale or when a new Product is Launched for sale. In that case, your system should be smart enough to handle the increasing load efficiently and that makes it Scalable.
In order to ensure scalability you should be able to compute the load that your system will experience. There are various factors that describe the Load on the System:
Go Over Specific Components And Details
At this stage you have a working design. Now let’s look at some of the specific components in detail.
Video Upload
Video content is the lifeblood of YouTube, and it doesn’t exist without it. This means that making it quick and easy for users to upload videos is probably the most important feature.
Imagine uploading a multi-gigabyte video to YouTube and then seeing the upload fail after 30 minutes when it’s 95% done. To prevent this you’ll want to support the ability for resuming uploads if the client’s connection is lost temporarily. The uploaded video can then be stored with a distributed file system like HDFS.
Once the upload is complete there’s still a lot more to do before the video is ready for users to access. The video needs to be encoded into multiple different quality formats, you need to generate thumbnails, and push copies of the video to the global CDN.
Again, at any stage one of these processes could fail. To prevent this you’ll have a task queue to manage this process and retry the processing attempt if it fails at any stage.
Database Scaling
The database is often the bottleneck of an application. You will probably be tested on whether you understand some of the fundamental concepts around database scaling. This could include caching to handle read requests, sharding, and replication.
Facebook System Design Interview Questions
Here are some commonly asked system design interview questions at :
Other frequently asked system design interview questions include topics on concurrency , caching, database partitioning, replication, sharding, CAP theorem, networking , real-world performance , availability and reliability , data storage and data aggregation, QPS capacity or machine estimation , and byte size estimation.
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What Companies Use System Design Interviews
Below, we’ve compiled a list of our interview guides for every company and role that we’ve covered, where system design interviews are used. This is not a comprehensive list of all companies in the industry that use system design interviews, but it does cover some of the biggest companies in the industry.
If you’d like to learn more about a specific company’s system design interviews, or their overall interview process, then we’d encourage you to check out our guide for that company below :
Caching At The Database Query Level
Whenever you query the database, hash the query as a key and store the result to the cache. This approach suffers from expiration issues:
- Hard to delete a cached result with complex queries
- If one piece of data changes such as a table cell, you need to delete all cached queries that might include the changed cell
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Amazon System Design Interview Questions
To get you started, here are a few Amazon system design interview questions.
Latency Numbers Every Programmer Should Know
Latency Comparison Numbers--------------------------L1 cache reference 0.5 nsBranch mispredict 5 nsL2 cache reference 7 ns 14x L1 cacheMutex lock/unlock 25 nsMain memory reference 100 ns 20x L2 cache, 200x L1 cacheCompress 1K bytes with Zippy 10,000 ns 10 usSend 1 KB bytes over 1 Gbps network 10,000 ns 10 usRead 4 KB randomly from SSD* 150,000 ns 150 us ~1GB/sec SSDRead 1 MB sequentially from memory 250,000 ns 250 usRound trip within same datacenter 500,000 ns 500 usRead 1 MB sequentially from SSD* 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memoryHDD seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtripRead 1 MB sequentially from 1 Gbps 10,000,000 ns 10,000 us 10 ms 40x memory, 10X SSDRead 1 MB sequentially from HDD 30,000,000 ns 30,000 us 30 ms 120x memory, 30X SSDSend packet CA-> Netherlands-> CA 150,000,000 ns 150,000 us 150 msNotes-----1 ns = 10^-9 seconds1 us = 10^-6 seconds = 1,000 ns1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns
Handy metrics based on numbers above:
Latency numbers visualized
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A Framework For The Systems Design Interview
System design interviews can feel intimidating, and having a framework on how to navigate them can help you feel more in control. The book recommends a 4-step process that I also agree with:
What Are Evaluated In A System Design Interview
We all know that a coding interview is focused on those basic knowledge of a candidate, so his general technical skills, analysis ability is tested.
However, few people can tell clearly the purpose of conducting system design interviews. So before jumping into tips, its better to understand system design interview from interviewers perspective.
In a system design interview, the candidate is often asked to design a new system in order to solve an open-ended problem like designing the URL shortening service. Sometimes the problem can be quite general like how do you design the recommended system for Youtube.
During this process, discussion is the core. The candidate is more likely to lead the conversation and discussion high-level components, details, pros and cons, and everything with the interviewer.
Compared to coding interview, system design interview is much more similar to software engineers daily work.
During the interview session, your communication and problem-solving ability are mainly evaluated. Given an open-ended problem, how do you analyze the issue, how do you solve it step by step, how do you explain your idea and discuss with others, how to you evaluate your system and optimize it are what interviewers mostly care.
So lets see what you can do to prepare for it.
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Bring It All Together
Before the end of your interview, you should take a few minutes to summarize your solution and highlight important bottlenecks or improvement opportunities.
A good way of going about this is to recap the goals and requirements you captured at the beginning of the interview, and then to highlight how your solution meets those objectives. At the same time, you should also highlight significant gaps or trade-offs in your design.
You can also briefly summarize how the system you’ve designed will work from end-to-end, to bring all of the elements of your design discussion together.
Taking these steps is a great way to refresh your interviewer’s memory, to demonstrate strong communication skills, and to show that you’ve kept a clear vision for the system’s goals throughout the entire interview.
Example Project From My Resume:
Built a timetable management system in Flask. The students and faculty can visualize their timetable, check for clashing courses as well as add their timetable to Google Calendar. Used pytest for unit testing. Travis builds and tests each commit to the GitHub repository. If the tests pass, it pushes the docker image to dockerhub and deploys the application to Heroku. Also setup ELK stack for monitoring and logging.
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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.”
Top 25 System Design Interview Questions And Answers
Following are frequently asked questions in interviews for freshers as well as experienced system designers.
1) What is System Design?
System design is a process of defining the elements of a system such as the architecture, components, modules, and various interfaces.
2) What are the three most essential skills of system designer?
Important skills for system designer are:
- User interaction
- Offline processes
3) How to design traffic control software?
To design a system for the traffic control system, as a software engineer, you need to make sure you know how to transition from one state to another. For example, Red to Green and from Green to Orange to Red, etc.
4) What is the benefit of a designing system like Pastebin?
Pastebin helps you design a system to paste code or text. You can share a link to that code anywhere you want. Its not an online code editor, yet you can use this, a tool to store any text.
5) As a system designer, how you can design a universal file sharing and storage apps like Google Drive or Dropbox?
The above mention apps are used to store and share files, photos, and other media. We can design things like allowing users to upload/search/view files or photos. It checks permissions for file sharing and enables multiple users to make changes in the same document.
6) How can you design an ATM system?
An ATM helps a user to deposit and withdraw money. It also allows users to see their account balance. You need to make a design plan to create this system.
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Round Robin And Weighted Round Robin
Another method that can be intuitively understood is called “round robin”. This is the way many humans process lists that loop. You start at the first item in the list, move down in sequence, and when you’re done with the last item you loop back up to the top and start working down the list again.
The load balancer can do this too, by just looping through available servers in a fixed sequence. This way the load is pretty evenly distributed across your servers in a simple-to-understand and predictable pattern.
You can get a little more “fancy” with the round robin by “weighting” some services over others. In the normal, standard round robin, each server is given equal weight . But when you differently weight servers, then you can have some servers with a lower weighting , and others can be higher like 0.7 or 0.9 or even 1.
Then the total traffic will be split up in proportion to those weights and allocated accordingly to the servers that have power proportionate to the volume of requests.
Section : Load Balancing
If you think about the two words, load and balance, you will start to get an intuition as to what this does in the world of computing. When a server simultaneously receives a lot of requests, it can slow down . After a point it may even fail .
You can give the server more muscle power or you can add more servers . But now you got to work out how the income requests get distributed to the various servers – which requests get routed to which servers and how to ensure they don’t get overloaded too? In other words, how do you balance and allocate the request load?
Enter load balancers. Since this article is an introduction to principles and concepts, they are, of necessity, very simplified explanations. A load balancer’s job is to sit between the client and server and work out how to distribute incoming request loads across multiple servers, so that the end user experience is consistently fast, smooth and reliable.
So load balancers are like traffic managers who direct traffic. And they do this to maintain availability and throughput.
When understanding where a load balancer is inserted in the system’s architecture, you can see that load balancers can be thought of as reverse proxies. But a load balancer can be inserted in other places too – between other exchanges – for example, between your server and your database.
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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.”
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Who Is This Post For
Apple is a large company and, therefore, hires to fill many different types of positions. Apple has a complete list of teams posted on Apples teams page.
This post will center on how to prepare for the software-focused roles, namely the Software and Services team.
The Software and Services team is split into a number of subcategories as well. A complete list of categories is provided on Apples Software and Services page.
Each subteam is specialized, and covering the subtopics in each goes well beyond the scope of this post.
For instance, if youre interested in working in the machine-learning division of the Software and Services team, expect specialized questions pertaining to artificial intelligence, algorithms specific to machine learning, and the like.
The common point among most, if not all, of these subservices is that they will require some flavor of technical interview. That is, you will be expected to have a deep understanding of the fundamentals of what is typically taught in an undergraduate degree program in computer science.
This includes a thorough understanding of data structures, algorithms, etc. For more information on what to expect for this style of interview in general, you can consult the list of blog posts provided by Byte by Byte.
This post is going to center on the specific aspects of the Apple Interview. We are going to investigate what makes Apple unique in their interview process and give you an overview of what to expect going in.
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How To Approach A System Design Interview Question
How to tackle a system design interview question.
The system design interview is an open-ended conversation. You are expected to lead it.
You can use the following steps to guide the discussion. To help solidify this process, work through the System design interview questions with solutions section using the following steps.
