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  • 🍔🧠 How Reddit Sends 10M+ Notifications/Month (Deep Dive)

🍔🧠 How Reddit Sends 10M+ Notifications/Month (Deep Dive)

PLUS: Claude AI Best Practices 📋, LLD Interview Blueprint 📘, CDN Explained 🌍

Author

Alex Zajac
August 25th, 2025 • Time-to-digest: 10 minutes

Happy Monday! ☀️

Welcome to the 175 new hungry minds who have joined us since last Monday!

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📚 Software Engineering Articles

🗞️ Tech and AI Trends

👨🏻‍💻 Coding Tip

  • Use awk with custom field separators to extract data from logs

Time-to-digest: 5 minutes

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Reddit built a sophisticated notification system that processes millions of posts daily to deliver personalized push notifications at scale. The system combines causal modeling, real-time retrieval, and deep learning to ensure users receive relevant content without notification fatigue.

The challenge: Balance user engagement with notification fatigue while processing millions of posts in real-time and maintaining high personalization accuracy.

Implementation highlights:

  1. Smart budgeting: Uses causal modeling to determine optimal daily notification limits per user

  2. Two-tower retrieval: Implements fast candidate selection using embedding-based similarity matching

  3. Multi-task learning: Employs deep neural networks to predict multiple engagement signals simultaneously

  4. Dynamic reranking: Applies product-driven adjustments to maintain content diversity and freshness

  5. Queue-based architecture: Ensures reliable delivery through asynchronous processing pipeline

Results and learnings:

  • Achieved real-time processing of millions of daily posts

  • Maintained high user engagement while minimizing notification fatigue

  • Successfully scaled to tens of millions of users with personalized delivery

Reddit's approach shows that building effective notification systems requires more than just technical prowess - it needs deep understanding of user behavior and engagement patterns. Their multi-stage pipeline demonstrates how to balance ML sophistication with practical product needs.

The 7 Must Know Patterns for System Design Interviews

When people prepare for coding interviews, it’s universally understood that patterns provide leverage.

7 Principles of Solution Architecture Design You Should Know

(5 Minutes) | Design principles that keep systems alive when reality hits

Developers, Reinvented – Thomas Dohmke

What started as fear of AI replacing developers is switching to pragmatically embracing the ambitious reality of AI and viewing it as a growth opportunity.

I Created the most Comprehensive LLD Interview Resource

I’m excited to launch my premium Low-Level Design interview resource, which I’ve been working on for the past 4 months.

5 Tiny Phrases Every Engineer Should Use With AI

How to prevent "AI Slop"

LLMs: Common terms explained, simply

What LLMs are, how they are trained, and how they can be used, visually explained!

Why I switched from Cursor to Claude Code

The future of coding isn’t autocomplete of AI. It’s collaboration with AI.

5 Things in Data Engineering That Still Hold True After 10 Years

Why core challenges in data engineering resist the test of time

ESSENTIAL (http-drama-queen)
HTTP is not simple

ARTICLE (retro-magic)
How to Run Great Retrospectives

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Brief: AWS CEO Matt Garman calls replacing junior employees with AI "the dumbest thing," arguing they’re cost-effective and key to future skill development, while advocating for AI as a tool for learning, not replacement.

Brief: AWS CEO Matt Garman slams the idea of replacing junior employees with AI, arguing they’re cost-effective and critical for long-term skill development, while advocating for AI as a training tool instead.

Brief: AGENTS.md is emerging as the standardized Markdown file for AI coding agents, providing project-specific instructions to complement traditional READMEs and streamline collaboration between developers and AI helpers.

Brief: Meta halts AI hiring after market turmoil and concerns over overinvestment, reversing its aggressive talent acquisition strategy that included $1B offers to top researchers.

Brief: Waymo secures critical permits to launch commercial autonomous rides in New York City, marking Alphabet's first robotaxi expansion to a dense urban environment.

This week’s coding challenge:

Build Your Own DNS Server

Real-world proficiency projects designed for experienced engineers. Develop software craftsmanship by recreating popular devtools from scratch.

This week’s tip:

Use awk pattern matching with custom field separators to extract structured data from messy logs using Extended Regular Expressions (ERE). The -F flag sets field separators, while pattern blocks like /pattern/{action} filter lines before processing.

Wen?

  • Legacy system analysis: Parse inconsistent log formats without writing custom parsers.

  • Quick data extraction: Pull specific fields from JSON-like logs without full parsing overhead.

  • Real-time monitoring: Filter and transform log streams on-the-fly in monitoring pipelines.

“We cannot change anything unless we accept it.”
Carl Jung

That’s it for today! ☀️

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See you in a week — Alex.

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