Reducing our monorepo size to improve developer velocity

Summary

Dropbox reduced its core server monorepo size from 87GB to 20GB after approaching GitHub's 100GB limit and suffering from hour-long clone times. The excessive bloat was traced to Git's delta compression heuristics interacting poorly with internationalization directory paths, generating inefficient diffs across different languages. By collaborating with GitHub to run an aggressive server-side repack with tuned window and depth settings, Dropbox cut clone times to under 15 minutes.

Takeaways

• Git's delta compression heuristic matches files based on the last 16 characters of their paths, which can generate bloated deltas if distinguishing path elements (like language codes) appear earlier.
• Client-side Git repacks do not improve remote clone and fetch performance because GitHub builds transfer packs dynamically using server-side configurations.
• Tuning Git repack parameters with higher window and depth values reduced repository size by 77% without requiring unsupported experimental flags.

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