Input features are the building blocks for machine learning models. You cannot have a great model without great features. By building on top of Apache Pulsar's infinite retention of events, we built infrastructure to serve features in production and to generate training datasets. It allowed our machine learning teams to change, test, and deploy personalization features at an extraordinary rate to 10s of millions of end-users. This talk will discuss: - What event-sourcing is and why it's so powerful for machine learning infrastructure. - How we built the StreamSQL feature store on top of Pulsar, Flink, and Cassandra. - How a feature store accelerates ML development.