Git 2.55 adds incremental MIDX writing, history fixup, Linux fsmonitor support

Git 2.55 has been released with a major update to repository management through incremental multi-pack index writing. Enabled with git repack --write-midx=incremental, the feature lets Git append new index layers for newly created packs instead of rewriting the entire MIDX file. When combined with geometric repacking, Git can use metadata-only compaction to keep MIDX chains efficient, compacting layers based on repack.midxSplitFactor and keeping growth logarithmic relative to repository size.

The experimental git history command also gains a new fixup subcommand, allowing users to fold staged changes into an earlier commit and replay later commits on top. This makes it easier to amend older commits without manually creating fixup commits and running an autosquash rebase. The command remains conservative, requiring a working tree and aborting when conflicts would occur.

Git 2.55 also improves workflow and performance across several areas. Config-based hooks can now run in parallel when enabled, while hooks that depend on shared state continue to run serially. Reachability bitmap generation is faster, with one large repository benchmark dropping from about 612 seconds to 294 seconds, and Linux now gains support for Git’s built-in filesystem monitor through inotify, helping speed up commands like git status when system watch limits are sufficient.