Chat Stability and Scalability

This post details the engineering challenges and solutions for scaling Facebook Chat to millions of users. It discusses the use of Erlang for its concurrency and distribution features, optimizations for memory footprint (e.g., using character arrays instead of linked lists, forced garbage collection before sleeping), and debugging C++ chatloggers that suffered from heap fragmentation due to excessive allocations from lexical_cast. It also covers the presence servers' bandwidth challenges, leading to zlib compression, and operational issues with load balancers causing connection resets and outages. The post highlights the addition of more load balancers as a solution and the implementation of monitoring tools like Scribe and fb303 for system health.