Safe at Any Speed: Building a Performant, Safe, Maintainable Packet Processor

Jane Street engineers optimized their OCaml-based market data distribution system to handle NASDAQ's peak load of 4 million messages per second while maintaining zero-allocation on critical paths to avoid garbage collection delays. By leveraging PPX preprocessors, immediate integer options, and a domain-specific language for protocol generation, the team reduced per-message processing latency from five microseconds to under 750 nanoseconds. This approach demonstrates that strict single-core, low-latency performance targets can be achieved with high-level functional languages through aggressive inlining and careful memory management rather than resorting to lower-level systems code.