Rewriting the heart of our sync engine

This post details the rationale and challenges behind rewriting Dropbox's core sync engine (Nucleus). It highlights issues with the legacy engine's data model, lack of testability, and difficulties in scaling. Key improvements in Nucleus include a cleaner data model, a single-threaded concurrency model with offloaded I/O for deterministic testing, and strategies to address durability and specification challenges in distributed file synchronization.