In this technical write-up, Taylor Blau guides readers through the most significant improvements and new features in Git 2.51, highlighting technical details and practical implications for developers and DevOps practitioners.

Key Updates in Git 2.51: Cruft-Free MIDX, Stash Interchange, and More

Taylor Blau covers the latest changes in Git 2.51, emphasizing impactful technical features and enhancements that developers and DevOps engineers can leverage in their workflows.

Cruft-Free Multi-Pack Indexes

Git 2.51 revises how unreachable objects (“cruft packs”) are managed in relation to the multi-pack index (MIDX). Previously, unreachable objects were stored separately, but if an object became reachable and only existed in the cruft pack, it couldn’t participate in reachability bitmaps. The new release ensures that non-cruft packs are “closed under reachability” by duplicating relevant objects as necessary, improving reliability and enabling smaller, faster MIDX files. Performance benefits observed at GitHub include MIDXs shrinking by ~38% and faster repository reads.

How to Use

Enable with the repack.MIDXMustContainCruft config option.
See upstream documentation.

Smaller Packs with Path Walk

Introducing “path walk” for pack generation, where objects are grouped by their path, replacing earlier hash heuristics.
Results in more effective delta compression and smaller pack sizes in some scenarios, without sacrificing performance.
Try with the --path-walk CLI option during repack.

Stash Interchange Format

Stash entries can now span multiple commits with a fourth parent linking to previous entries.
Enables exporting stashes to a reference for syncing between machines (git stash export --to-ref, git stash import).
Practical for multi-environment or collaborative use cases.

Additional Updates

git cat-file Improvements: Now correctly reports submodule objects, enhancing scripting capabilities.
Bloom Filter Enhancements: Commit-graph Bloom filters now support multiple pathspecs in git log, increasing query efficiency.
Stable Commands: git switch and git restore transition from experimental status, guaranteeing CLI stability.
Deprecation Notices: git whatchanged is deprecated; use git log --raw or the --i-still-use-this flag in the meantime.
Preparations for Git 3.0: Default hash for new repos will be SHA-256; reftable backend to become standard.
C99 Feature Adoption: The project now uses C99 features such as the bool keyword more broadly, continuing incremental adoption for consistency and code modernization.
Patch Submission Guidelines: Contributors can now submit under names other than their legal name, aligning with broader open source practices.