#6 Things Every Backend Engineer Should Know (That AI Won't Tell You)

AI can write code. Honestly, it can write it faster and with fewer syntax errors than most of us. But here's what it can't do: it doesn't know your system's traffic patterns, your database's growth trajectory, your team's ops maturity, or why that one service falls over every Tuesday at 2 AM. Architecture is still yours to own. This post is aimed at backend engineers — especially those in the Java/Spring Boot world — who want to go beyond CRUD and understand what actually makes systems hold up under pressure. 1. 🧵 Thread Pool Sizing — Bigger Is Not Better "more threads = more throughput.? " It doesn't work that way. CPU-bound vs. IO-bound — why it matters Your app's tasks fall into two categories: CPU-bound — number crunching, encoding, compression. The thread needs the CPU the whole time. IO-bound — database calls, HTTP requests, file reads. The thread spends most of its time waiting. If your app is CPU-bound and you run 200 threads on a 6-core machine, each core is constantly switch