Loading…
Tag
#Cassandra
2 posts
April 22, 2026
How Big Tech Checks Username Uniqueness at Billion-User Scale
When you type a username and instantly see 'already taken', there's a multi-layer stack doing the work: a probabilistic filter, an in-memory cache, a distributed index, and a load balancer in front of all of them. This post breaks down each data structure, its trade-offs, and how Google, Meta, and Amazon combine them to answer one simple yes/no question in milliseconds across billions of users.
System DesignBloom FilterRedis
April 5, 2026
Netflix Uses Cassandra. Instagram Uses PostgreSQL. Twitter Uses Redis. They're All Right.
Netflix writes 3M records/sec. Instagram serves a billion users. Twitter handles 300K timeline reads/sec. Each picked a radically different database — not because one is better, but because their access patterns are fundamentally different. This post reverse-engineers all three architectures and gives you a mental framework for making these decisions yourself.
System DesignDatabasesCassandra