System Design Posts | >hacksubset

How Gmail Knows Your Username Is Taken Before You Finish Typing

I got curious about how Gmail checks email availability across billions of accounts in real time. Turns out the answer involves a data structure I'd only ever seen in textbooks.

Anindra

• Sep 7, 2026

System Design

Splitwise Low Level Design in Java: Complete LLD Guide

A full Splitwise LLD walkthrough for system design interviews, entity modeling, design patterns, the balance simplification algorithm, and a complete Java implementation you can run.

Anindra

• Apr 06, 2026

Tag: System Design

How Gmail Knows Your Username Is Taken Before You Finish Typing

Splitwise Low Level Design in Java: Complete LLD Guide