1. Important Dates (Must Remember)YearEvent336 BCAlexander became king of Macedon327 BCInvaded India326 BCBattle with Porus326 BCSoldiers revolted at Beas River325 BCReturned from India323 BCAlexander died at SusaTrick"36 → 27 → 26 → 25 → 23"336 → Became King327 → Entered India326 → Fo

Perfect.This is where everything you’ve learned finally comes together into a REAL banking-grade design.Today we’ll cover:Ledger-based system design — how banks actually store and protect moneyNo fluff. This is core financial system architecture.? LEDGER-BASED SYSTEM DESIGN1️⃣ The Biggest 

Excellent.Day 7 is one of the most practical days — this is where we eliminate an entire class of production bugs by changing how we write SQL.Today’s focus:Avoid Read → Modify → Write bugs using ATOMIC SQL UPDATES? DAY 7 — ATOMIC SQL UPDATES1️⃣ The Core Problem (MOST COMMON BUG)❌ Re

Perfect.Day 5 is one of the MOST important days — this is where many “it works in testing but fails in production” bugs come from.I’ll explain Isolation Levels in a way you can feel what the database is doing.TRANSACTION ISOLATION LEVELSIsolation = how much of other transactions your transac

I was learning about deadlock and found that when multiple threads locks the same row in that situation, it creates deadlock. So I asked chatgpt that what if 500 managers are working on 100 bank accounts simultaneously, will it cause deadlock and how to avoid it? Chatgpt replied:Short answer first

Deadlocks: When Safety Itself Freezes the System“Deadlocks happen not because code is unsafe, but because it is too safe in the wrong order.”Yesterday you learned how to lock correctly.Today you learn what happens when locks fight each other.1️⃣ What Is a Deadlock (Plain English)A deadlock h

✅ 1️⃣ What Day 2 Was AboutDay 2 topic: IdempotencyHow to make sure the same request executed multiple times does NOT corrupt dataThis sits between Day 1 (why systems fail) and Day 3 (race conditions).✅ 2️⃣ What Was Covered in Day 2 (Explicitly)✔ Meaning of “method called twice”User

Excellent question.This shows you’re thinking at the exact point where many engineers level up.Short answer first, then the real answer:NO — you don’t always have to run a direct UPDATE.YES — you must ensure the read–check–write is ATOMIC.There are two correct ways to avoid unsafe “rea