Background In Part 1, we established that access patterns & not entities should drive your design. In Part 2, we fixed the database by replacing brittle three-table JOINs with a covering index, reducing P99 on the listing query. The schema was right. The index was right. The listing API itself was fast. And then it …

Background In the first part we established the foundational principle that separates systems which survive scale from systems that collapse under it - design for access patterns, not for entities. In this second part we double click on the database design of the User Profile system and try to understand its impact …

Background Architecture decisions rarely break at design time. They break a year later, under double the load, when an unwritten assumption proves false. I’ve seen this play out in synchronous coupling, storage models, and service splits - while architecting and designing FinTech platforms. That’s why I now run every …

Background This multi part series walks through the real architectural decisions and real mistakes behind designing a globally distributed KYC User Profile system - a system that should be capable of serving billions of users at 10M+ RPD with sub-500 ms P99 latency. It's mainly about weighing trade-offs and making …