Fast ACS - Low-Latency File-Based Ordered Message Delivery at Scale

Learn about Fast ACS, a file-based ordered message delivery system designed for low-latency communication at massive scale in this 16-minute conference presentation from USENIX ATC '25. Discover how Google engineers developed a robust messaging system that transmits data across clusters and efficiently delivers it to thousands of consumers while maintaining ordering guarantees and at-least-once delivery. Explore the innovative design that combines two-sided inter-cluster communication using Remote Procedure Calls with one-sided intra-cluster communication via Remote Memory Access to achieve optimal performance. Understand how this production-deployed system scales to accommodate several thousand consumers per cluster, handling Tbps-scale intra-cluster traffic while delivering messages globally within seconds or sub-seconds at p99 latency. Examine the technical architecture that enables real-time systems to handle data distribution across metropolitan and continental boundaries without overloading consumers, allowing them to process messages at their own pace while maintaining low resource costs.