Neo Kim

Here are some probabilistic data structures you must know as a software engineer (not kidding):

They trade accuracy for space efficiency.

They're often used in:

• Databases

• Cache

• Search engines

• Network infrastructure

• Analytics

What else should make this list?

If you want to reduce latency, learn these 12 rules:

How DNS Works 🔥 #70: Distributed Hierarchical Database for 5.35B Users (2 Minutes)

👋 PS - I wrote a more detailed article about DNS in my newsletter (with visuals):

→ newsletter.systemdesign.one/p/what-is-a-dns-server-and-how-does-it-work

Give me 2 mins and I'll teach you how DNS works:

Meta achieves 99.99999999% cache consistency.

Here’s how they do it (in 2 minutes):

——

👋 PS - I put together a detailed case study with visuals in my newsletter:

→ newsletter.systemdesign.one/p/cache-cons...

Give me 2 mins and I'll teach you how Disney+ Hotstar scaled to 25M concurrent users—no fluff:

How I’d scale a site to 1 million users—step by step:

Hey, it's a pleasant surprise to see you on bsky

HTTP Status Codes Cheatsheet

HTTP status codes you must know as a web developer in 2025:

Status codes are 3-digit numbers returned by a server in response to HTTP requests.

It tells the client about the request status and indicates problems if any.

So understanding status codes will help you find site errors quickly.

This lady:

• Has no tech background
• Couldn't draw well as a kid
• Knew nothing about venture capitalists

Yet she's worth $5.8 Billion - at 37.

I'm Type 3 and You?

How to write clean code.

The KYD-DTC Playbook:

Give me 2 mins and I'll teach you how a database stores passwords securely (not kidding):

Give me 2 mins and I'll teach you how Amazon S3 (actually) works:

How Apple Pay Handles 41 Million Transactions a Day Securely 💸 #68: Break Into Apple Pay Architecture (5 Minutes)

👋 PS - I wrote an article with visuals about this case study in my newsletter:

→ newsletter.systemdesign.one/p/how-does-a...

I spent hours studying how Apple Pay works, so you don't have to.

Here's what I learned distilled into 9 sentences:

• Google Drive → Nextcloud

• Microsoft Outlook → Thunderbird

• LastPass → KeePass

• YouTube → PeerTube

• Adobe Premiere Pro → Kdenlive

• Visual Studio → Vim

• Trello → Taiga

• Evernote → Joplin

Popular apps and open-source alternatives:

What else should make this list?

• Microsoft Office → Libre Office

• WhatsApp → Signal

• Google Chrome → Mozilla Firefox

• Adobe Photoshop → Krita

• Google → DuckDuckGo

• Windows / Mac → GNU Linux