Explore the journey of improving Mercurial's performance through Rust implementation in this 46-minute conference talk from linux.conf.au 2021. Dive into the challenges and solutions encountered during the rewrite of core components, particularly the 'hg status' command, which achieved a 25x speed improvement. Learn about Rust and Python interoperability, efficient data structures, directory traversal optimization, version control internals, and platform-specific issues. Gain insights into append-only binary formats, mtime caching, safe memory mapping in concurrent contexts, and multithreading techniques. Discover how this rewrite effort significantly enhanced Mercurial's scalability and performance for large repositories.