Posts Tagged ‘JordanMiller’
[reClojure2025] Datomic at Nubank: Simplicity Scaled
Lecturer
Jordan Miller is a Staff Software Engineer at Nubank, where she is a core member of the Datomic team, specifically focusing on developer success and the evolution of the database product. Jordan is a prominent figure in the Clojure community, serving as the co-founder of Clojure Camp, a co-author of Clojure Brain Teasers, and the producer/host of the Lost In Lambduhhs podcast. Her professional background is marked by a deep passion for functional programming and a commitment to making complex technical systems accessible to a wider audience.
Abstract
Since its acquisition by Nubank in 2020, Datomic has transitioned from a specialized tool for discerning architects to the foundational storage layer of one of the world’s largest independent banks. This article explores the symbiotic relationship between Nubank’s mission to simplify banking and Datomic’s philosophy of data-driven simplicity. We analyze the technical challenges of scaling Datomic to serve over 114 million customers, focusing on innovations such as “implicit partitions” and the architectural shifts required to maintain a global-scale financial system. Furthermore, we examine how the “Datomic-as-a-Service” model within Nubank empowers thousands of developers to build resilient, high-performance microservices while maintaining the lowest cost-to-serve in the banking industry.
Simplicity as a Mission: The Nubank and Datomic Alignment
The acquisition of Cognitect (the creators of Clojure and Datomic) by Nubank was more than a corporate transaction; it was a meeting of shared values. Nubank was founded with the explicit goal of reducing the extreme complexity and high costs of the Brazilian banking sector. At the time, millions of Brazilians were unbanked, and interest rates for personal loans often exceeded 100% per year. Nubank sought to disrupt this by building a bank that was digital-first, customer-centric, and architecturally simple.
Datomic, with its focus on immutability, “database-as-a-value,” and the separation of reads from writes, provided the perfect technical backbone for this mission. Jordan highlights that the alignment on “simplicity” allowed the partnership to flourish. Today, Nubank serves 114.3 million users with an 83% activity rate, largely fueled by word-of-mouth referrals. The bank’s ability to scale rapidly while maintaining the lowest cost-to-serve globally is a direct consequence of an architecture that prioritizes developer productivity and system reliability through Datomic.
Architectural Innovation: Scaling the Immutable Store
Scaling a database to handle the needs of over 100 million customers requires rethinking traditional storage patterns. Within Nubank, Datomic is not just a database; it is a managed service provided to over 3,000 developers working across 1,000 microservices. This “Datomic-as-a-Service” (DaaS) model ensures that individual product teams do not need to worry about provisioning or maintaining their own database clusters.
A key innovation discussed by Jordan is the concept of implicit partitions. In standard Datomic, partitions are a way to group related data for better locality and performance. However, as the number of services and the volume of data grew at Nubank, manual partition management became a bottleneck. The Datomic team developed implicit partitions to automate this process, allowing the system to handle massive growth without manual intervention. This technical advancement is part of a broader effort to make Datomic “invisible” to the developer, allowing them to focus on business logic rather than storage mechanics.
The Power of “Database-as-a-Value”
The fundamental innovation of Datomic—treating the database as an immutable value—is what enables Nubank’s high-scale operations. In a traditional SQL database, “the” database is a moving target that changes with every update. In Datomic, a process can take a “snapshot” of the database at a specific point in time and perform complex queries against that static value. This eliminates many of the concurrency issues found in traditional systems and makes it trivial to implement features like “time-travel” auditing, which is critical for financial compliance.
Developer Success and the Future of Datomic
Jordan’s role at Nubank emphasizes that the success of a technology is as much about the people using it as it is about the code itself. The Datomic team at Nubank is committed to “Developer Success,” which involves building tools, documentation, and a culture that helps engineers leverage the database effectively. This includes the creation of a “Datomic Workshop” and active engagement with the Clojure community to ensure that Datomic continues to evolve as a world-class product.
The results of this focus are evident in Nubank’s operational efficiency. By providing a unified, simple, and powerful storage abstraction, Nubank has managed to grow by an average of 13 million customers per year since 2015 while keeping its infrastructure costs significantly lower than traditional banks. This demonstrates that functional programming and immutable databases are not just academic curiosities but are viable, high-performance solutions for the world’s most demanding financial environments.