This presentation explores how Nubank, the world's largest independent digital bank, achieves unprecedented scale and efficiency by leveraging Datomic and Closure. Beginning with the 2020 acquisition of Cognitech and Daytomic, the speaker highlights the foundational alignment between Nubank's mission to simplify banking and Daytomic's philosophy of simplicity. The talk details Nubank's rapid growth, serving over 114 million users with an exceptionally low cost-to-serve, largely driven by word-of-mouth referrals due to its impact on financial inclusion in Brazil. Technically, Nubank manages petabytes of data across thousands of Datomic databases and microservices, processing billions of daily events. The core of "scaling simplicity" is broken down into architectural, performance, and people-process scalability. Architectural scalability is exemplified by Datomic's peer model, which distributes read loads horizontally. Performance enhancements are demonstrated through new Datomic features like "transactor hints" and "implicit partitions," which reduce I/O and improve data locality. The presentation concludes by reinforcing the synergy between Nubank's values and Daytomic's design, enabling safe development by thousands of engineers and empowering millions financially.
Scaling Simplicity: How Nubank Achieves Massive Scale with Datomic and Closure
0:17 Nubank's Strategic Acquisition of Daytomic: In 2020, Nubank acquired Cognitech and Daytomic, finding a deep alignment between Nubank's mission to simplify banking for Brazilians and Daytomic's philosophy of simplicity and software. This partnership has since led to significant growth in the Daytomic team.
1:06 Personal Experience of Nubank's Impact: The speaker recounts a challenging public transport experience in SΓ£o Paulo where only Nubank's purple cards consistently worked at kiosks, illustrating the bank's profound and widespread impact on real people.
2:12 Unprecedented Growth and Efficiency: As of April 2025, Nubank serves 114.3 million users, an increase of over 20 million from 2023, sustaining an 83% activity rate. It boasts the lowest cost to serve globally among independent banks, adding nearly 13 million customers annually since 2015, with 80% of growth from word-of-mouth referrals.
3:24 Addressing Financial Exclusion: Nubank emerged in a Brazilian market characterized by high retail lending interest rates (often over 100% annually) and significant financial exclusion (45 million unbanked in 2017). For millions, Nubank provided their first credit card, savings account, or loan.
4:13 Massive Technical Scale: Nubank handles petabytes of data, operates over 3,000 Datomic databases (some with over 100 billion "datoms"), runs 4,000 microservices on Kubernetes, processes 72 billion daily Kafka events, and routinely manages millions of requests per second, all while adhering to strict banking compliance.
5:07 Nubank as a Tech Company: Recognized as more of a tech company than a bank, Nubank employs over 8,700 people, including 3,000+ engineers, across six countries.
6:27 Defining Scaling vs. Growth: The presentation differentiates between "growth" (increasing revenue by proportionally increasing resources) and "scaling" (increasing output while proportionally reducing resources), aligning with Nubank's value of "pursuing smart efficiency." Nubank's efficiency ratio is 29.9%, half the industry average.
8:00 Three Types of Scalability: Nubank focuses on:
Architectural Scalability: Systems grow without redesign, staying performant under load.
Performance Scalability: Increasing throughput without increasing latency or cost.
People Process Scalability: Human problems don't hinder system development or deployment.
9:09 Datomic's Peer Model for Architectural Scalability: Unlike traditional databases that cluster/shard, Datomic employs a "peer model" where read operations are distributed among capable peer nodes. This allows for arbitrary horizontal scaling of reads and aggressive caching while maintaining consistency, reducing the load on a central monolithic server.
11:17 Performance Scalability with New Datomic Features:
Transaction Stats and IO Stats: Built-in observability tools to measure and tune real-world performance.
15:36 Transactor Hints (First Implemented Oct 2024): This feature allows peers to speculatively determine and send necessary read requests to the transactor while transactions are queued, significantly reducing I/O on main threads and shortening latency (like curbside pickup for groceries).
17:15 Implicit Partitions (Released April 2023): Improves data locality by allowing applications to group entities, meaning queries can efficiently retrieve relevant data by reading fewer segments, leading to faster database performance (like a well-organized salad bar).
20:25 Conclusion: The Power of "Scaling Simplicity": Nubank's success, running on Closure and Datomic, is attributed to the alignment of its values (simplicity, smart efficiency, fanatical customer focus) with the underlying technology. This synergy enables thousands of engineers to ship safely, empowering millions with financial tools they previously lacked, with 74% of users reporting improved financial health.
23:40 Daytomic's Broader Impact and Resources: Daytomic operates as a product outside Nubank, serving other major clients like Netflix and HSBC. Resources for learning Datomic, including a YouTube playlist, free access, support, and monthly meetups, are highlighted.