Forem: Arthur Rio

Leetcode - Weekly Contest #395

Arthur Rio — Sat, 27 Apr 2024 12:11:44 +0000

Hey folks, how are you doing?

For those who already know, this is just a reminder. For those who don't, every week Leetcode has a special contest where a lot of developers try to solve 4 code challenges in a row in 1 hour 30 min.

It's 2 easy questions, 1 medium question, and 1 hard question.

Try it, even if you can't finish all the questions, because sometimes you can find these questions in your interviews. This has already happened to me before.

Leetcode also has a ranking if you plan to get a better position and challenge yourself!

Biweekly Contest at 02:3pm(14:30) UTC

Weekly Contest at 02:30am(02:30) UTC

Have a great weekend, and good luck!

Interview Question: Best Size for a Thread Pool?

Arthur Rio — Mon, 08 Apr 2024 16:01:36 +0000

Introduction

This week I did an interview process where I needed to answer the question: Determine a threadpool size to handle 5000 requests where each request takes 10 milliseconds. This is a common problem in a production environment; every day we need to think about how I can scale a microservice or how many microservice instances I should use. If just increasing the number of threads would be the best solution, I will not talk about concurrency and parallelism. Today I'll focus on how to solve this in case someday I need to come back here 👍🏻

Solution

It's hard to determine the right size for a threadpool. What I could do is estimate the closest size that answers the question, but creating a scenario that does not exist, where I have a server with UNLIMITED resources, and my goal is just to reach 5000 requests per second (RPS) where the response time is 10ms, so I should use this formula:

Creating a formula based in requests per second

If each request took one second, to handle 5000 requests in one second, our server would need to create 5000 threads. (Remember, this is just a fictional scenario to make it easy to understand)

$\frac{\text{Threadpool size}}{\text{response time in seconds}}$

$\frac{5000}{1} = \text{5000 requests(threads)/s}$

Therefore, each response only takes 10 milliseconds, and we need to achieve a performance of 5000 requests per second. If 1 second = 1000 milliseconds, then 10 milliseconds = 0.01s = 1/100s

$\text{10 milliseconds} = 0.01s =\frac{1}{100}\text{seconds}$

So we just adjust the formula:

$\frac{\text{Threadpool size}}{\text{response time in seconds}}$

$\text{Threadpool size} = \text{Performance (RPS)} * \text{(response time)}$

$\text{Threadpool size} = 5000 * \frac{1}{100} = 50$

Conclusion

Remember, to answer this question should clarify that we can't easily determine the right threadpool size based on response time and the throughput an app wants to achieve. When we think about achieving better throughput, first, we should identify all bottlenecks, which could be a database, an API, or even an algorithm. Pay attention to the server's limits like CPU-bound, Memory RAM-bound, and I/O bound, as all these limits will determine how many threads your system can handle. We should consider whether our server is shared with other apps/systems. Increasing the number of threads without taking all these factors into consideration may not meet expectations or even create a point of failure in the system. And we are not talking about concurrency and parallelism, which is an awesome topic related to this one.

This is just a short answer. In another post, I could bring more details about it and take all the factors mentioned above into consideration, along with other examples.

I hope that you enjoyed it, and all comments are welcome, if possible with a reference to a book or post to enrich the post that is open to editing and improvements!

I will leave some references below.

Resources

Java Concurrency in Pratice - Chap. 8

Latency Numbers Programmer Should Know: Crash Course System Design #1 - YouTube

Weekly system design newsletter: https://bit.ly/3tfAlYDCheckout our bestselling System Design Interview books: Volume 1: https://amzn.to/3Ou7gkdVolume 2: htt...

youtube.com

From Brazil to NYC: Tech Career & Life as a Software Engineer

Arthur Rio — Mon, 08 Apr 2024 15:39:58 +0000

Welcome, everyone! I've launched this platform to offer insights into my daily life. I'm Arthur, a Brazilian Software Engineer now based in New York City for over a year. Through my posts, I'll tell you about my journey, delving a into the immigrant experience, differences in job interviews between Brazil and the U.S., and sharing valuable insights into software engineering, including system design, architecture, and best practices.

Lately, my focus has been on honing my skills in algorithms and data structures while navigating job interviews in the U.S. This journey has taught me valuable lessons in time management and productivity.

Additionally, I'd like to recommend some websites I frequently use for practice:

Neetcode - Offers a comprehensive roadmap.
Leetcode - The LeetCode Explorer course serves as an excellent guide for choosing relevant courses.
BigOcheatsheet - Provides insights into time complexity.
tryhackme - An excellent resource for learning about information security.
ByteByteGo - A valuable system design reference.
Refactoring.guru - Insights into design patterns.

Stay tuned for more updates!