How PayPal Was Able to Support a Billion Transactions per Day With Only 8 Virtual Machines

PayPal scaled to a billion daily transactions with only 8 virtual machines. Initially a security software team for handheld devices that pivoted to create PayPal, they struggled with scalability using traditional hardware. Transitioning to the actor model based on the Akka framework in Java allowed them to handle extreme scale efficiently. The actor model is a conceptual concurrency model where lightweight actors process messages, isolated from one another, improving performance and fault tolerance. PayPal's adaptation of the actor model optimized resource usage, simplified scalability, and enhanced error handling. The approach provides an overview of how PayPal overcame scalability challenges through innovative system design.