Pgrust was built: four attempts to rewrite Postgres in Rust with AI (malisper.me)

After four intensive attempts costing approximately $100,000, developers successfully created "pgrust," a Rust-based version of the PostgreSQL database, aided significantly by AI tools like OpenAI’s Codex. The significance of this endeavor lies in demonstrating that AI can effectively facilitate the rewriting of complex legacy systems to improve performance and maintainability. The final version of pgrust features 1.8 million lines of idiomatic Rust code and shows promising results, being faster than traditional Postgres for transactional tasks and competitive with Clickhouse for analytical queries. The process involved multiple strategies, starting with direct feature porting which proved unsustainable due to fundamental issues in architecture. The team transitioned to using c2rust for a line-by-line transpilation from C to Rust, achieving ABI compatibility with the existing Postgres ecosystem. However, the challenge remained when attempting to refactor the resulting unsafe Rust code into idiomatic Rust, leading to an incremental rewriting approach that focused on gradual rehabilitation of components. The development journey of pgrust serves as a valuable case study for the AI/ML community, showcasing the complexities and potential of rewriting legacy software with AI assistance.