Improving storage efficiency in Magic Pocket, our immutable blob store

Dropbox's server monorepo grew to 87GB, slowing down engineering velocity due to long clone times and approaching the 100GB GitHub limit. The team discovered that Git's delta compression was inefficiently storing internationalization files, causing rapid repository growth. A locally tested fix using an experimental flag reduced the repository size to 20GB, but further investigation showed that this solution was incompatible with GitHub's server-side optimizations.

Dropbox's engineering team optimized Dash's relevance judge using DSPy, a framework for systematically optimizing prompts against a measurable objective. To adapt their existing judge for a lower-cost model, they defined a clear objective (minimizing disagreement with human relevance judgments while ensuring usable outputs) and used DSPy's GEPA optimizer to generate structured feedback for each example where the model disagreed with humans. This prompted a repeatable optimization loop, resulting in a more reliable and cheaper judge for production use.