[{"data":1,"prerenderedAt":787},["ShallowReactive",2],{"/en-us/blog/whats-new-in-git-2-49-0":3,"navigation-en-us":37,"banner-en-us":436,"footer-en-us":446,"blog-post-authors-en-us-Toon Claes":688,"blog-related-posts-en-us-whats-new-in-git-2-49-0":702,"assessment-promotions-en-us":737,"next-steps-en-us":777},{"id":4,"title":5,"authorSlugs":6,"body":8,"categorySlug":9,"config":10,"content":14,"description":8,"extension":26,"isFeatured":12,"meta":27,"navigation":12,"path":28,"publishedDate":20,"seo":29,"stem":34,"tagSlugs":35,"__hash__":36},"blogPosts/en-us/blog/whats-new-in-git-2-49-0.yml","Whats New In Git 2 49 0",[7],"toon-claes",null,"open-source",{"slug":11,"featured":12,"template":13},"whats-new-in-git-2-49-0",true,"BlogPost",{"title":15,"description":16,"authors":17,"heroImage":19,"date":20,"body":21,"category":9,"tags":22},"What's new in Git 2.49.0?","Learn about the latest version of Git, including improved performance thanks to zlib-ng, a new name-hashing algorithm, and git-backfill(1).",[18],"Toon Claes","https://res.cloudinary.com/about-gitlab-com/image/upload/v1749663087/Blog/Hero%20Images/git3-cover.png","2025-03-14","The Git project recently released [Git 2.49.0](https://lore.kernel.org/git/xmqqfrjfilc8.fsf@gitster.g/). Let's look at a few notable highlights from this release, which includes contributions from GitLab's Git team and the wider Git community.\n\nWhat's covered:\n- [git-backfill(1) and the new path-walk API](#git-backfill(1)-and-the-new-path-walk-api)\n- [Introduction of zlib-ng](#introduction-of-zlib-ng)\n- [Continued iteration on Meson](#continued-iteration-on-meson)\n- [Deprecation of .git/branches/ and .git/remotes/](#deprecation-of-.gitbranches%2F-and-.git%2Fremotes%2F)\n- [Rust bindings for libgit](#rust-bindings-for-libgit)\n- [New name-hashing algorithm](#new-name-hashing-algorithm)\n- [Promisor remote capability](#promisor-remote-capability)\n- [Thin clone using `--revision`](#thin-clone-using---revision)\n\n## git-backfill(1) and the new path-walk API\n\nWhen you [`git-clone(1)`](https://git-scm.com/docs/git-clone) a Git repository,\nyou can pass it the\n[`--filter`](https://git-scm.com/docs/git-clone#Documentation/git-clone.txt-code--filterltfilter-specgtcode)\noption. Using this option allows you to create a _partial clone_. In a partial\nclone the server only sends a subset of reachable objects according to the given\nobject filter. For example, creating a clone with `--filter=blob:none` will not\nfetch any blobs (file contents) from the server and create a _blobless clone_.\n\nBlobless clones have all the reachable commits and trees, but no blobs. When you\nperform an operation like\n[`git-checkout(1)`](https://git-scm.com/docs/git-checkout), Git will download\nthe missing blobs to complete that operation. For some operations, like\n[`git-blame(1)`](https://git-scm.com/docs/git-blame), this might result in\ndownloading objects one by one, which will slow down the command drastically.\nThis performance degradation occurs because `git-blame(1)` must traverse the\ncommit history to identify which specific blobs it needs, then request each\nmissing blob from the server separately.\n\nIn Git 2.49, a new subcommand `git-backfill(1)` is introduced, which can be\nused to download missing blobs in a blobless partial clone.\n\nUnder the hood, the `git-backfill(1)` command leverages the new path-walk API, which is different from how Git generally iterates over commits. Rather than iterating over the commits one at a time and recursively visiting the trees and blobs associated with each commit, the path-walk API does traversal by path. For each path, it adds a list of associated tree objects to a stack. This stack is then processed in a depth-first order. So, instead of processing every object in commit `1` before moving to commit `2`, it will process all versions of file `A` across all commits before moving to file `B`. This approach greatly improves performance in scenarios where grouping by path is essential.\n\nLet me demonstrate its use by making a blobless clone of [`gitlab-org/git`](https://gitlab.com/gitlab-org/git):\n\n```shell\n$ git clone --filter=blob:none --bare --no-tags git@gitlab.com:gitlab-org/git.git\nCloning into bare repository 'git.git'...\nremote: Enumerating objects: 245904, done.\nremote: Counting objects: 100% (1736/1736), done.\nremote: Compressing objects: 100% (276/276), done.\nremote: Total 245904 (delta 1591), reused 1547 (delta 1459), pack-reused 244168 (from 1)\nReceiving objects: 100% (245904/245904), 59.35 MiB | 15.96 MiB/s, done.\nResolving deltas: 100% (161482/161482), done.\n```\n\nAbove, we use `--bare` to ensure Git doesn't need to download any blobs to check\nout an initial branch. We can verify this clone does not contain any blobs:\n\n```sh\n$ git cat-file --batch-all-objects --batch-check='%(objecttype)' | sort | uniq -c\n  83977 commit\n 161927 tree\n```\n\nIf you want to see the contents of a file in the repository, Git has to download it:\n\n```sh\n$ git cat-file -p HEAD:README.md\nremote: Enumerating objects: 1, done.\nremote: Total 1 (delta 0), reused 0 (delta 0), pack-reused 1 (from 1)\nReceiving objects: 100% (1/1), 1.64 KiB | 1.64 MiB/s, done.\n\n[![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)\n\nGit - fast, scalable, distributed revision control system\n=========================================================\n\nGit is a fast, scalable, distributed revision control system with an\nunusually rich command set that provides both high-level operations\nand full access to internals.\n\n[snip]\n```\n\nAs you can see above, Git first talks to the remote repository to download the blob before\nit can display it.\n\nWhen you would like to `git-blame(1)` that file, it needs to download a lot\nmore:\n\n```sh\n$ git blame HEAD README.md\nremote: Enumerating objects: 1, done.\nremote: Counting objects: 100% (1/1), done.\nremote: Total 1 (delta 0), reused 0 (delta 0), pack-reused 0 (from 0)\nReceiving objects: 100% (1/1), 1.64 KiB | 1.64 MiB/s, done.\nremote: Enumerating objects: 1, done.\nremote: Counting objects: 100% (1/1), done.\nremote: Total 1 (delta 0), reused 0 (delta 0), pack-reused 0 (from 0)\nReceiving objects: 100% (1/1), 1.64 KiB | 1.64 MiB/s, done.\nremote: Enumerating objects: 1, done.\nremote: Counting objects: 100% (1/1), done.\nremote: Total 1 (delta 0), reused 0 (delta 0), pack-reused 0 (from 0)\nReceiving objects: 100% (1/1), 1.64 KiB | 1.64 MiB/s, done.\nremote: Enumerating objects: 1, done.\n\n[snip]\n\ndf7375d772 README.md (Ævar Arnfjörð Bjarmason 2021-11-23 17:29:09 +0100  1) [![Build status](https://github.com/git/git/workflows/CI/badge.svg)](https://github.com/git/git/actions?query=branch%3Amaster+event%3Apush)\n5f7864663b README.md (Johannes Schindelin \t2019-01-29 06:19:32 -0800  2)\n28513c4f56 README.md (Matthieu Moy        \t2016-02-25 09:37:29 +0100  3) Git - fast, scalable, distributed revision control system\n28513c4f56 README.md (Matthieu Moy        \t2016-02-25 09:37:29 +0100  4) =========================================================\n556b6600b2 README\t(Nicolas Pitre       \t2007-01-17 13:04:39 -0500  5)\n556b6600b2 README\t(Nicolas Pitre       \t2007-01-17 13:04:39 -0500  6) Git is a fast, scalable, distributed revision control system with an\n556b6600b2 README\t(Nicolas Pitre       \t2007-01-17 13:04:39 -0500  7) unusually rich command set that provides both high-level operations\n556b6600b2 README\t(Nicolas Pitre       \t2007-01-17 13:04:39 -0500  8) and full access to internals.\n556b6600b2 README\t(Nicolas Pitre       \t2007-01-17 13:04:39 -0500  9)\n\n[snip]\n```\n\nWe've truncated the output, but as you can see, Git goes to the server for each\nrevision of that file separately. That's really inefficient. With\n`git-backfill(1)` we can ask Git to download all blobs:\n\n```shell\n$ git backfill\nremote: Enumerating objects: 50711, done.\nremote: Counting objects: 100% (15438/15438), done.\nremote: Compressing objects: 100% (708/708), done.\nremote: Total 50711 (delta 15154), reused 14730 (delta 14730), pack-reused 35273 (from 1)\nReceiving objects: 100% (50711/50711), 11.62 MiB | 12.28 MiB/s, done.\nResolving deltas: 100% (49154/49154), done.\nremote: Enumerating objects: 50017, done.\nremote: Counting objects: 100% (10826/10826), done.\nremote: Compressing objects: 100% (634/634), done.\nremote: Total 50017 (delta 10580), reused 10192 (delta 10192), pack-reused 39191 (from 1)\nReceiving objects: 100% (50017/50017), 12.17 MiB | 12.33 MiB/s, done.\nResolving deltas: 100% (48301/48301), done.\nremote: Enumerating objects: 47303, done.\nremote: Counting objects: 100% (7311/7311), done.\nremote: Compressing objects: 100% (618/618), done.\nremote: Total 47303 (delta 7021), reused 6693 (delta 6693), pack-reused 39992 (from 1)\nReceiving objects: 100% (47303/47303), 40.84 MiB | 15.26 MiB/s, done.\nResolving deltas: 100% (43788/43788), done.\n```\n\nThis backfills all blobs, turning the blobless clone into a full clone:\n\n```shell\n$ git cat-file --batch-all-objects --batch-check='%(objecttype)' | sort | uniq -c\n 148031 blob\n  83977 commit\n 161927 tree\n```\n\nThis [project](https://lore.kernel.org/git/pull.1820.v3.git.1738602667.gitgitgadget@gmail.com/)\nwas led by [Derrick Stolee](https://stolee.dev/) and was merged with\n[e565f37553](https://gitlab.com/gitlab-org/git/-/commit/e565f3755342caf1d21e22359eaf09ec11d8c0ae).\n\n## Introduction of zlib-ng\n\nAll objects in the `.git/` folder are compressed by Git using [`zlib`](https://zlib.net/). `zlib` is the reference implementation for the [RFC\n1950](https://datatracker.ietf.org/doc/html/rfc1950): ZLIB Compressed Data\nFormat. Created in 1995, `zlib` has a long history and is incredibly\nportable, even supporting many systems that predate the Internet. Because of its\nwide support of architectures and compilers, it has limitations in what it is\ncapable of.\n\nThe fork [`zlib-ng`](https://github.com/zlib-ng/zlib-ng) was created to\naccommodate the limitations. `zlib-ng` aims to be optimized for modern\nsystems. This fork drops support for legacy systems and instead brings in\npatches for Intel optimizations, some Cloudflare optimizations, and a couple\nother smaller patches.\n\nThe `zlib-ng` library itself provides a compatibility layer for `zlib`. The\ncompatibility later allows `zlib-ng` to be a drop-in replacement for `zlib`, but\nthat layer is not available on all Linux distributions. In Git 2.49:\n\n- A compatibility layer was added to the Git project.\n- Build options were added to both to the [`Makefile`](https://gitlab.com/gitlab-org/git/-/blob/b9d6f64393275b505937a8621a6cc4875adde8e0/Makefile#L186-187)\n  and [Meson Build file](https://gitlab.com/gitlab-org/git/-/blob/b9d6f64393275b505937a8621a6cc4875adde8e0/meson.build#L795-811).\n\nThese additions make it easier to benefit from the performance improvements of\n`zlib-ng`.\n\nIn local benchmarks, we've seen a ~25% speedup when using `zlib-ng` instead of `zlib`. And we're in the process of rolling out these changes to\nGitLab.com, too.\n\nIf you want to benefit from the gains of `zlib-ng`, first verify if Git\non your machine is already using `zlib-ng` by running\n`git version --build-options`:\n\n```shell\n$ git version --build-options\ngit version 2.47.1\ncpu: x86_64\nno commit associated with this build\nsizeof-long: 8\nsizeof-size_t: 8\nshell-path: /bin/sh\nlibcurl: 8.6.0\nOpenSSL: OpenSSL 3.2.2 4 Jun 2024\nzlib: 1.3.1.zlib-ng\n```\n\nIf the last line includes `zlib-ng` then your Git is already built\nusing the faster `zlib` variant. If not, you can either:\n\n- Ask the maintainer of the Git package you are using to include `zlib-ng` support.\n- Build Git yourself from source.\n\nThese [changes](https://gitlab.com/gitlab-org/git/-/commit/9d0e81e2ae3bd7f6d8a655be53c2396d7af3d2b0)\nwere [introduced](https://lore.kernel.org/git/20250128-b4-pks-compat-drop-uncompress2-v4-0-129bc36ae8f5@pks.im/)\nby [Patrick Steinhardt](https://gitlab.com/pks-gitlab).\n\n## Continued iteration on Meson\n\nIn our article about the Git 2.48 release,\nwe touched on [the introduction of the Meson build system](https://about.gitlab.com/blog/whats-new-in-git-2-48-0/#meson-build-system). [Meson](https://en.wikipedia.org/wiki/Meson_(software)) is\na build automation tool used by the Git project that at some point might replace [Autoconf](https://en.wikipedia.org/wiki/Autoconf),\n[CMake](https://en.wikipedia.org/wiki/CMake), and maybe even\n[Make](https://en.wikipedia.org/wiki/Make_(software)).\n\nDuring this release cycle, work continued on using Meson, adding various missing\nfeatures and stabilization fixes:\n\n  - [Improved test coverage for\n\tCI](https://lore.kernel.org/git/20250122-b4-pks-meson-additions-v3-0-5a51eb5d3dcd@pks.im/)\n\twas merged in\n\t[72f1ddfbc9](https://gitlab.com/gitlab-org/git/-/commit/72f1ddfbc95b47c6011bb423e6947418d1d72709).\n  - [Bits and pieces to use Meson in `contrib/`](https://lore.kernel.org/git/20250219-b4-pks-meson-contrib-v2-0-1ba5d7fde0b9@pks.im/)\n\twere merged in\n\t[2a1530a953](https://gitlab.com/gitlab-org/git/-/commit/2a1530a953cc4d2ae62416db86c545c7ccb73ace).\n  - [Assorted fixes and improvements to the build procedure based on\n\tmeson](https://lore.kernel.org/git/20250226-b4-pks-meson-improvements-v3-0-60c77cf673ae@pks.im/)\n\twere merged in\n\t[ab09eddf60](https://gitlab.com/gitlab-org/git/-/commit/ab09eddf601501290b5c719574fbe6c02314631f).\n  - [Making Meson aware of building\n\t`git-subtree(1)`](https://lore.kernel.org/git/20250117-b4-pks-build-subtree-v1-0-03c2ed6cc42e@pks.im/)\n\twas merged in\n\t[3ddeb7f337](https://gitlab.com/gitlab-org/git/-/commit/3ddeb7f3373ae0e309d9df62ada24375afa456c7).\n  - [Learn Meson to generate HTML documentation\n\tpages](https://lore.kernel.org/git/20241227-b4-pks-meson-docs-v2-0-f61e63edbfa1@pks.im/)\n\twas merged in\n\t[1b4e9a5f8b](https://gitlab.com/gitlab-org/git/-/commit/1b4e9a5f8b5f048972c21fe8acafe0404096f694).\n\nAll these efforts were carried out by [Patrick Steinhardt](https://gitlab.com/pks-gitlab).\n\n## Deprecation of .git/branches/ and .git/remotes/\n\nYou are probably aware of the existence of the `.git` directory, and what is\ninside. But have you ever heard about the sub-directories `.git/branches/` and\n`.git/remotes/`? As you might know, reference to branches are stored in\n`.git/refs/heads/`, so that's not what `.git/branches/` is for, and what about\n`.git/remotes/`?\n\nWay back in 2005, [`.git/branches/`](https://git-scm.com/docs/git-fetch#_named_file_in_git_dirbranches)\nwas introduced to store a shorthand name for a remote, and a few months later they were\nmoved to [`.git/remotes/`](https://git-scm.com/docs/git-fetch#_named_file_in_git_dirremotes).\nIn [2006](https://lore.kernel.org/git/Pine.LNX.4.63.0604301520460.2646@wbgn013.biozentrum.uni-wuerzburg.de/),\n[`git-config(1)`](https://git-scm.com/docs/git-config) learned to store\n[remotes](https://git-scm.com/docs/git-config#Documentation/git-config.txt-remoteltnamegturl).\nThis has become the standard way to configure remotes and, in 2011, the\ndirectories `.git/branches/` and `.git/remotes/` were\n[documented](https://gitlab.com/git-scm/git/-/commit/3d3d282146e13f2d7f055ad056956fd8e5d7ed29#e615263aaf131d42be8b0d0888ebd3fec954c6c9_132_124)\nas being \"legacy\" and no longer used in modern repositories.\n\nIn 2024, the document [BreakingChanges](https://git-scm.com/docs/BreakingChanges)\nwas started to outline breaking changes for the next major version of Git\n(v3.0). While this release is not planned to happen any time soon, this document\nkeeps track of changes that are expected to be part of that release.\nIn [8ccc75c245](https://gitlab.com/git-scm/git/-/commit/8ccc75c2452b5814d2445d60d54266293ca48674),\nthe use of the directories `.git/branches/` and `.git/remotes/` was added to\nthis document and that officially marks as them deprecated and to be removed in\nGit 3.0.\n\nThanks to [Patrick Steinhardt](https://gitlab.com/pks-gitlab) for\n[formalizing this deprecation](https://lore.kernel.org/git/20250122-pks-remote-branches-deprecation-v4-5-5cbf5b28afd5@pks.im/).\n\n## Rust bindings for libgit\n\nWhen compiling Git, an internal library `libgit.a` is made. This library\ncontains some of the core functionality of Git.\n\nWhile this library (and most of Git) is written in C, in Git 2.49 bindings were\nadded to make some of these functions available in Rust. To achieve this, two\nnew Cargo packages were created: `libgit-sys` and `libgit-rs`. These packages\nlive in the [`contrib/`](https://gitlab.com/gitlab-org/git/-/tree/master/contrib) subdirectory in the Git source tree.\n\nIt's pretty\n[common](https://doc.rust-lang.org/cargo/reference/build-scripts.html#-sys-packages)\nto split out a library into two packages when a [Foreign Function\nInterface](https://en.wikipedia.org/wiki/Foreign_function_interface) is used.\nThe `libgit-sys` package provides the pure interface to C functions and links to\nthe native `libgit.a` library. The package `libgit-rs` provides a high-level\ninterface to the functions in `libgit-sys` with a feel that is more idiomatic to\nRust.\n\nSo far, the functionality in these Rust packages is very limited. It only\nprovides an interface to interact with the `git-config(1)`.\n\nThis initiative was led by [Josh Steadmon](https://lore.kernel.org/git/8793ff64a7f6c4c04dd03b71162a85849feda944.1738187176.git.steadmon@google.com/) and was merged with [a4af0b6288](https://gitlab.com/gitlab-org/git/-/commit/a4af0b6288e25eb327ae9018cee09def9e43f1cd).\n\n## New name-hashing algorithm\n\nThe Git object database in `.git/` stores most of its data in packfiles. And\npackfiles are also used to submit objects between Git server and client over the\nwire.\n\nYou can read all about the format at\n[`gitformat-pack(5)`](https://git-scm.com/docs/gitformat-pack). One important\naspect of the packfiles is delta-compression. With delta-compression not every\nobject is stored as-is, but some objects are saved as a _delta_ of another\n_base_. So instead of saving the full contents of the objects, changes compared\nto another object are stored.\n\nWithout going into the details how these deltas are calculated or stored, you\ncan imagine that it is important group files together that are very similar. In\nv2.48 and earlier, Git looked at the last 16 characters of the path name to\ndetermine whether blobs might be similar. This algorithm is named version `1`.\n\nIn Git 2.49, version `2` is available. This is an iteration on version `1`, but\nmodified so the effect of the parent directory is reduced. You can specify the\nname-hash algorithm version you want to use with option `--name-hash-version` of\n[`git-repack(1)`](https://git-scm.com/docs/git-repack).\n\n[Derrick Stolee](https://stolee.dev/), who drove this project, did some\ncomparison in resulting packfile size after running `git repack -adf\n--name-hash-version=\u003Cn>`:\n\n| Repo                                          \t| Version 1 size   | Version 2 size |\n|---------------------------------------------------|-----------|---------|\n| [fluentui](https://github.com/microsoft/fluentui) | 440 MB \t| 161 MB   |\n| Repo B                                        \t| 6,248 MB   | 856 MB   |\n| Repo C                                        \t| 37,278 MB  | 6,921 MB |\n| Repo D                                        \t| 131,204 MB | 7,463 MB |\n\nYou can read more of the details in the [patch\nset](https://lore.kernel.org/git/pull.1823.v4.git.1738004554.gitgitgadget@gmail.com/),\nwhich is merged in\n[aae91a86fb](https://gitlab.com/gitlab-org/git/-/commit/aae91a86fb2a71ff89a71b63ccec3a947b26ca51).\n\n## Promisor remote capability\n\nIt's known that Git isn't great in dealing with large files. There are some\nsolutions to this problem, like [Git LFS](https://git-lfs.com/), but there are\nstill some shortcomings. To give a few:\n\n- With Git LFS the user has to configure which files to put in LFS. The server has\n  no control about that and has to serve all files.\n- Whenever a file is committed to the repository, there is no way to get it out\n  again without rewriting history. This is annoying, especially for large files,\n  because they are stuck for eternity.\n- Users cannot change their mind on which files to put into Git LFS.\n- A tool like Git LFS requires significant effort to set up, learn, and use\n  correctly.\n\nFor some time, Git has had the concept of promisor remotes. This feature can be used to deal with large files, and in Git 2.49 this feature took a step forward.\n\nThe idea for the new “promisor-remote” capability is relatively simple: Instead of sending all\nobjects itself, a Git server can tell to the Git client \"Hey, go download these\nobjects from _XYZ_\". _XYZ_ would be a promisor remote.\n\nGit 2.49 enables the server to advertise the information of the promisor remote\nto the client. This change is an extension to\n[`gitprotocol-v2`](https://git-scm.com/docs/gitprotocol-v2). While the server\nand the client are transmitting data to each other, the server can send  names and URLs of the promisor remotes it knows\nabout.\n\nSo far, the client is not using the promisor remote info it gets from the server during clone, so all\nobjects are still transmitted from the remote the clone initiated from. We are planning to continue work on this feature, making it use promisor remote info from the server, and making it easier to use.\n\nThis [patch\nset](https://lore.kernel.org/git/20250218113204.2847463-1-christian.couder@gmail.com/)\nwas submitted by [Christian Couder](https://gitlab.com/chriscool) and merged\nwith\n[2c6fd30198](https://gitlab.com/gitlab-org/git/-/commit/2c6fd30198187c928cbf927802556908c381799c).\n\n## Thin clone using `--revision`\n\nA new `--revision` option was added to\n[`git-clone(1)`](https://git-scm.com/docs/git-clone). This enables you to create\na thin clone of a repository that only contains the history of the given\nrevision. The option is similar to `--branch`, but accepts a ref name (like\n`refs/heads/main`, `refs/tags/v1.0`, and `refs/merge-requests/123`) or a\nhexadecimal commit object ID. The difference to `--branch` is that it does not\ncreate a tracking branch and detaches `HEAD`. This means it's not suited if you\nwant to contribute back to that branch.\n\nYou can use `--revision` in combination with `--depth` to create a very minimal\nclone. A suggested use-case is for automated testing. When you have a CI system\nthat needs to check out a branch (or any reference) to perform autonomous\ntesting on the source code, having a minimal clone is all you need.\n\nThis\n[change](https://gitlab.com/gitlab-org/git/-/commit/5785d9143bcb3ef19452a83bc2e870ff3d5ed95a)\nwas\n[driven](https://lore.kernel.org/git/20250206-toon-clone-refs-v7-0-4622b7392202@iotcl.com/)\nby [Toon Claes](https://gitlab.com/toon).\n\n# Read more\n- [What’s new in Git 2.48.0?](https://about.gitlab.com/blog/whats-new-in-git-2-48-0/)\n- [What’s new in Git 2.47.0?](https://about.gitlab.com/blog/whats-new-in-git-2-47-0/)\n- [What’s new in Git 2.46.0?](https://about.gitlab.com/blog/whats-new-in-git-2-46-0/)",[23,24,25],"community","open 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Let's look at a few notable highlights from this release, which includes\ncontributions from the Git team at GitLab.\n\n## Geometric repacking support with promisor remotes\n\nNewly written objects in a Git repository are often stored as individual loose files. To ensure good performance and optimal use of disk space, these loose objects are regularly compressed into so-called packfiles. The number of packfiles in a repository grows over time as a result of the user’s activities, like writing new commits or fetching from a remote. As the number of packfiles in a repository increases, Git has to do more work to look up individual objects. Therefore, to preserve optimal repository performance, packfiles are periodically repacked via git-repack(1) to consolidate the objects into fewer packfiles. When repacking there are two strategies: “all-into-one” and “geometric”.\n\nThe all-into-one strategy is fairly straightforward and the current default. As its name implies, all objects in the repository are packed into a single packfile. From a performance perspective this is great for the repository as Git only has to scan through a single packfile when looking up objects. The main downside of such a repacking strategy is that computing a single packfile for a repository can take a significant amount of time for large repositories.\n\nThe geometric strategy helps mitigate this concern by maintaining a geometric progression of packfiles based on their size instead of always repacking into a single packfile. To explain more plainly, when repacking Git maintains a set of packfiles ordered by size where each packfile in the sequence is expected to be at least twice the size of the preceding packfile. If a packfile in the sequence violates this property, packfiles are combined as needed until the progression is restored. This strategy has the advantage of still minimizing the number of packfiles in a repository while also minimizing the amount of work that must be done for most repacking operations.\n\nOne problem with the geometric repacking strategy was that it was not compatible with partial clones. Partial clones allow the user to clone only parts of a repository by, for example, skipping all blobs larger than 1 megabyte. This can significantly reduce the size of a repository, and Git knows how to backfill missing objects that it needs to access at a later point in time.\n\nThe result is a repository that is missing some objects, and any object that may not be fully connected is stored in a “promisor” packfile.  When repacking, this promisor property needs to be retained going forward for packfiles containing a promisor object so it is known whether a missing object is expected and can be backfilled from the promisor remote. With an all-into-one repack, Git knows how to handle promisor objects properly and stores them in a separate promisor packfile. Unfortunately, the geometric repacking strategy did not know to give special treatment to promisor packfiles and instead would merge them with normal packfiles without considering whether they reference promisor objects. Luckily, due to a bug the underlying git-pack-objects(1) dies when using geometric repacking in a partial clone repository. So this means repositories in this configuration were not able to be repacked anyways which isn’t great, but better than repository corruption.\n\nWith the release of Git 2.53, geometric repacking now works with partial clone repositories. When performing a geometric repack, promisor packfiles are handled separately in order to preserve the promisor marker and repacked following a separate geometric progression. With this fix, the geometric strategy moves closer towards becoming the default repacking strategy. For more information check out the corresponding [mailing list thread](https://lore.kernel.org/git/20260105-pks-geometric-repack-with-promisors-v1-0-c4660573437e@pks.im/).\n\nThis project was led by [Patrick Steinhardt](https://gitlab.com/pks-gitlab).\n\n## git-fast-import(1) learned to preserve only valid signatures\n\nIn our [Git 2.52 release article](https://about.gitlab.com/blog/whats-new-in-git-2-52-0/), we covered signature related improvements to git-fast-import(1) and git-fast-export(1). Be sure to check out that post for a more detailed explanation of these commands, how they are used, and the changes being made with regards to signatures.\n\nTo quickly recap, git-fast-import(1) provides a backend to efficiently import data into a repository and is used by tools such as [git-filter-repo(1)](https://github.com/newren/git-filter-repo) to help rewrite the history of a repository in bulk. In the Git 2.52 release, git-fast-import(1) learned the `--signed-commits=\u003Cmode>` option similar to the same option in git-fast-export(1). With this option, it became possible to unconditionally retain or strip signatures from commits/tags.\n\nIn situations where only part of the repository history has been rewritten, any signature for rewritten commits/tags becomes invalid. This means git-fast-import(1) is limited to either stripping all signatures or keeping all signatures even if they have become invalid. But retaining invalid signatures doesn’t make much sense, so rewriting history with git-repo-filter(1) results in all signatures being stripped, even if the underlying commit/tag is not rewritten. This is unfortunate because if the commit/tag is unchanged, its signature is still valid and thus there is no real reason to strip it. What is really needed is a means to preserve signatures for unchanged objects, but strip invalid ones.\n\nWith the release of Git 2.53, the git-fast-import(1) `--signed-commits=\u003Cmode>` option has learned a new `strip-if-invalid` mode which, when specified, only strips signatures from commits that become invalid due to being rewritten. Thus, with this option it becomes possible to preserve some commit signatures when using git-fast-import(1). This is a critical step towards providing the foundation for tools like git-repo-filter(1) to preserve valid signatures and eventually re-sign invalid signatures.\n\nThis project was led by [Christian Couder](https://gitlab.com/chriscool).\n\n## More data collected in git-repo-structure\n\nIn the Git 2.52 release, the “structure” subcommand was introduced to git-repo(1). The intent of this command was to collect information about the repository and eventually become a native replacement for tools such as [git-sizer(1)](https://github.com/github/git-sizer). At GitLab, we host some extremely large repositories, and having insight into the general structure of a repository is critical to understand its performance characteristics. In this release, the command now also collects total size information for reachable objects in a repository to help understand the overall size of the repository. In the output below, you can see the command now collects both the total inflated and disk sizes of reachable objects by object type.\n\n```shell\n$ git repo structure\n\n| Repository structure | Value      |\n| -------------------- | ---------- |\n| * References         |            |\n|   * Count            |   1.78 k   |\n|     * Branches       |      5     |\n|     * Tags           |   1.03 k   |\n|     * Remotes        |    749     |\n|     * Others         |      0     |\n|                      |            |\n| * Reachable objects  |            |\n|   * Count            | 421.37 k   |\n|     * Commits        |  88.03 k   |\n|     * Trees          | 169.95 k   |\n|     * Blobs          | 162.40 k   |\n|     * Tags           |    994     |\n|   * Inflated size    |   7.61 GiB |\n|     * Commits        |  60.95 MiB |\n|     * Trees          |   2.44 GiB |\n|     * Blobs          |   5.11 GiB |\n|     * Tags           | 731.73 KiB |\n|   * Disk size        | 301.50 MiB |\n|     * Commits        |  33.57 MiB |\n|     * Trees          |  77.92 MiB |\n|     * Blobs          | 189.44 MiB |\n|     * Tags           | 578.13 KiB |\n```\n\nThe keen-eyed among you may have also noticed that the size values in the table output are also now listed in a more human-friendly manner with units appended. In subsequent releases we hope to further expand this command's output to provide additional data points such as the largest individual objects in the repository.\n\nThis project was led by [Justin Tobler](https://gitlab.com/justintobler).\n\n## Read more\n\nThis article highlighted just a few of the contributions made by GitLab and\nthe wider Git community for this latest release. You can learn about these from\nthe [official release announcement](https://lore.kernel.org/git/xmqq4inz13e3.fsf@gitster.g/T/#u) of the Git project. Also, check\nout our [previous Git release blog posts](https://about.gitlab.com/blog/tags/git/)\nto see other past highlights of contributions from GitLab team members.",[24,25,23],{"featured":12,"template":13,"slug":713},"whats-new-in-git-2-53-0",{"content":715,"config":724},{"title":716,"description":717,"authors":718,"heroImage":19,"date":721,"body":722,"category":9,"tags":723},"What’s new in Git 2.52.0?","Learn about release contributions, including the new git-last-modified(1) command, improvements to history-rewriting tools, and a new maintenance strategy.",[719,18,720],"Christian Couder","Patrick Steinhardt","2025-11-17","The Git project recently released [Git 2.52](https://lore.kernel.org/git/xmqqh5usmvsd.fsf@gitster.g/). After a relatively short 8-week [release cycle for 2.51](https://about.gitlab.com/blog/what-s-new-in-git-2-51-0/), due to summer in the Northern Hemisphere, this release is back to the usual 12-week cycle. Let’s look at some notable changes, including contributions from the GitLab Git team and the wider Git community.\n\n## New git-last-modified(1) command\n\nMany Git forges like GitLab display files in a tree view like this:\n\n\n| Name        | Last commit                                             | Last update  |\n| ------------- | --------------------------------------------------------- | -------------- |\n| README.md   | README: *.txt -> *.adoc fixes                           | 4 months ago |\n| RelNotes    | Start 2.51 cycle, the first batch                       | 4 weeks ago  |\n| SECURITY.md | SECURITY: describe how to report vulnerabilities        | 4 years      |\n| abspath.c   | abspath: move related functions to abspath              | 2 years      |\n| abspath.h   | abspath: move related functions to abspath              | 2 years      |\n| aclocal.m4  | configure: use AC_LANG_PROGRAM consistently             | 15 years ago |\n| add-patch.c | pager: stop using `the_repository`                      | 7 months ago |\n| advice.c    | advice: allow disabling default branch name advice      | 4 months ago |\n| advice.h    | advice: allow disabling default branch name advice      | 4 months ago |\n| alias.h     | rebase -m: fix serialization of strategy options        | 2 years      |\n| alloc.h     | git-compat-util: move alloc macros to git-compat-util.h | 2 years ago  |\n| apply.c     | apply: only write intents to add for new files          | 8 days ago   |\n| archive.c   | Merge branch 'ps/parse-options-integers'                | 3 months ago |\n| archive.h   | archive.h: remove unnecessary include                   | 1 year       |\n| attr.h      | fuzz: port fuzz-parse-attr-line from OSS-Fuzz           | 9 months ago |\n| banned.h    | banned.h: mark `strtok()` and `strtok_r()` as banned    | 2 years      |\n\n\n\u003Cbr>\u003C/br>\n\nNext to the files themselves, we also display which commit last modified each respective file. This information is easy to extract from Git by executing the following command:\n\n\n```shell\n\n$ git log --max-count=1 HEAD -- \u003Cfilename>\n\n```\n\nWhile nice and simple, this has a significant catch: Git does not have a way to extract this information for each of these files in a single command. So to get the last commit for all the files in the tree, we'd need to run this command for each file separately. This results in a command pipeline similar to the following:\n\n```shell\n\n$ git ls-tree HEAD --name-only | xargs --max-args=1 git log --max-count=1 HEAD --\n\n```\n\nNaturally, this isn't very efficient:\n\n\n* We need to spin up a fresh Git command for each file.\n\n\n* Git has to step through history for each file separately.\n\n\n\nAs a consequence, this whole operation is quite costly and generates significant load for GitLab.\n\n\n\nTo overcome these issues, a new Git subcommand `git-last-modified(1)` has been introduced. This command returns the commit for each file of a given commit:\n\n\n\n```shell\n\n$ git last-modified HEAD\n\n\ne56f6dcd7b4c90192018e848d0810f091d092913        add-patch.c\n373ad8917beb99dc643b6e7f5c117a294384a57e        advice.h\ne9330ae4b820147c98e723399e9438c8bee60a80        advice.c\n5e2feb5ca692c5c4d39b11e1ffa056911dd7dfd3        alloc.h\n954d33a9757fcfab723a824116902f1eb16e05f7        RelNotes\n4ce0caa7cc27d50ee1bedf1dff03f13be4c54c1f        apply.c\n5d215a7b3eb0a9a69c0cb9aa43dcae956a0aa03e        archive.c\nc50fbb2dd225e7e82abba4380423ae105089f4d7        README.md\n72686d4e5e9a7236b9716368d86fae5bf1ae6156        attr.h\nc2c4138c07ca4d5ffc41ace0bfda0f189d3e262e        archive.h\n5d1344b4973c8ea4904005f3bb51a47334ebb370        abspath.c\n5d1344b4973c8ea4904005f3bb51a47334ebb370        abspath.h\n60ff56f50372c1498718938ef504e744fe011ffb        banned.h\n4960e5c7bdd399e791353bc6c551f09298746f61        alias.h\n2e99b1e383d2da56c81d7ab7dd849e9dab5b7bf0        SECURITY.md\n1e58dba142c673c59fbb9d10aeecf62217d4fc9c        aclocal.m4\n```\n\n\n\nThe benefit of this is obviously that we only have to execute a single Git process now to derive all of that information. But even more importantly, it only requires us to walk the history once for all files together instead of having to walk it multiple times. This is achieved by:\n\n\n1. Start walking the history from the specified commit.\n\n\n2. For each commit:\n   1. If it doesn't modify any of the paths we're interested in we continue to the next commit.\n   2. If it does, we print the commit ID together with the path. Furthermore, we remove the path from the set of interesting paths.\n3. When the list of interesting paths becomes empty we stop.\n\n\n\nGitaly has already been adjusted to use the new command, but the logic is still guarded by a feature flag. Preliminary testing has shown that `git-last-modified(1)` is in most situations at least twice as fast compared to using `git log --max-count=1`.\n\n\n\n*These changes were [originally written](https://github.com/ttaylorr/git/tree/tb/blame-tree) by multiple developers from GitHub and were [upstreamed](https://lore.kernel.org/git/20250805093358.1791633-1-toon@iotcl.com/) into Git by [Toon Claes](https://gitlab.com/toon).*\n\n\n\n## git-fast-export(1) and git-fast-import(1) signature-related improvements\n\n\n\nThe `git-fast-export(1)` and `git-fast-import(1)` commands are designed to be mostly used by interoperability or history rewriting tools. The goal of interoperability tools is to make Git interact nicely with other software, usually a different version control system, that stores data in a different format than Git. For example [hg-fast-export.sh](https://github.com/frej/fast-export) is a “Mercurial to Git converter using git-fast-import.\"\n\n\n\nAlternately, history-rewriting tools let users — usually admins — make changes to the history of their repositories that are not possible or not allowed by the version control system. For example, [reposurgeon](http://www.catb.org/esr/reposurgeon/) says in its [introduction](https://gitlab.com/esr/reposurgeon/-/blob/master/repository-editing.adoc?ref_type=heads#introduction) that its purpose is “to enable risky operations that version-control systems don't want to let you do, such as (a) editing past comments and metadata, (b) excising commits, (c) coalescing and splitting commits, (d) removing files and subtrees from repo history, (e) merging or grafting two or more repos, and (f) cutting a repo in two by cutting a parent-child link, preserving the branch structure of both child repos.\"\n\n\n\nWithin GitLab, we use [git-filter-repo](https://github.com/newren/git-filter-repo) to let admins perform some risky operations on their Git repositories. Unfortunately, until Git 2.50 (released last June), both `git-fast-export(1)` and `git-fast-import(1)` didn't handle cryptographic commit signatures at all. So, although `git-fast-export(1)` had a `--signed-tags=\u003Cmode>` option that allows users to change how cryptographic tag signatures are handled, commit signatures were simply ignored.\n\n\n\nCryptographic signatures are very fragile because they are based on the exact commit or tag data that was signed. When the signed data or any of its preceding history changes, the cryptographic signature becomes invalid. This is a fragile but necessary requirement to make these signatures useful.\n\n\n\nBut in the context of rewriting history this is a problem:\n\n\n\n* We may want to keep cryptographic signatures for both commits and tags that are still valid after the rewrite (e.g. because the history leading up to them did not change).\n\n\n* We may want to create new cryptographic signatures for commits and tags where the previous signature has become invalid.\n\n\n\nNeither `git-fast-import(1)` nor `git-fast-export(1)` allow for these use cases though, which limits what tools like [git-filter-repo](https://github.com/newren/git-filter-repo) or [reposurgeon](http://www.catb.org/esr/reposurgeon/) can achieve.\n\n\n\nWe have made some significant progress:\n\n\n\n* In Git 2.50 we added a `--signed-commits=\u003Cmode>` option to `git-fast-export(1)` for exporting commit signatures, and support in `git-fast-import(1)` for importing them.\n\n\n* In Git 2.51 we improved the format used for exporting and importing commit signatures, and we made it possible for `git-fast-import(1)` to import both a signature made on the SHA-1 object ID of the commit and one made on its SHA-256 object ID.\n\n\n* In Git 2.52 we added the `--signed-commits=\u003Cmode>` and `--signed-tags=\u003Cmode>` options to `git-fast-import(1)`, so the user has control over how to handle signed data at import time.\n\n\n\nThere is still more to be done. We need to add the ability to:\n\n\n\n* Retain only those commit signatures that are still valid to `git-fast-import(1)`.\n\n\n* Re-sign data where the signature became invalid.\n\n\n\nWe have already started to work on these next steps and expect this to land in Git 2.53. Once done, tools like `git-filter-repo(1)` will finally start to handle cryptographic signatures more gracefully. We will keep you posted in our next Git release blog post.\n\n\n\n*This project was led by [Christian Couder](https://gitlab.com/chriscool).*\n\n\n\n## New and improved git-maintenance(1) strategies\n\n\n\nGit repositories require regular maintenance to ensure that they perform well. This maintenance performs a bunch of different tasks: references get optimized, objects get compressed, and stale data gets pruned.\n\n\n\nUntil Git 2.28, these maintenance tasks were performed by `git-gc(1)`. The problem with this command is that it wasn't built with customizability in mind: While certain parameters can be configured, it is not possible to control which parts of a repository should be optimized. This means that it may not be a good fit for all use cases. Even more importantly, it made it very hard to iterate on how exactly Git performs repository maintenance.\n\n\n\nTo fix this issue and allow us to iterate again, [Derrick Stolee](https://github.com/derrickstolee) introduced `git-maintenance(1)`. In contrast to `git-gc(1),` it is built with customizability in mind and allows the user to configure which tasks specifically should be running in a certain repository. This new tool was made the default for Git’s automated maintenance in Git 2.29, but, by default, it still uses `git-gc(1)` to perform the maintenance.\n\n\n\nWhile this default maintenance strategy works well in small or even medium-sized repositories, it is problematic in the context of large monorepos. The biggest limiting factor is how `git-gc(1)` repacks objects: Whenever there are more than 50 packfiles, the tool will merge all of them together into a single packfile. This operation is quite CPU-intensive and causes a lot of I/O operations, so for large monorepos this operation can easily take many minutes or even hours to complete.\n\n\n\nGit already knows how to minimize these repacks via “geometric repacking.” The idea is simple: The packfiles that exist in the repository must follow a geometric progression where every packfile must contain at least twice as many objects as the next smaller one. This allows Git to amortize the number of repacks required while still ensuring that there is only a relatively small number of packfiles overall. This mode was introduced by [Taylor Blau](https://github.com/ttaylorr) in Git 2.32, but it was not wired up as part of the automated maintenance.\n\n\n\nAll the parts exist to make repository maintenance way more scalable for large monorepos: We have the flexible `git-maintenance(1)` tool that can be extended to have a new maintenance strategy, and we have a better way to repack objects. All that needs to be done is to combine these two.\n\n\n\nAnd that's exactly what we did with Git 2.52! We have introduced a new “geometric” maintenance strategy that you can configure in your Git repositories. This strategy is intended as a full replacement for the old strategy based on `git-gc(1)`. Here is the config code you need:\n\n\n\n```shell\n\n$ git config set maintenance.strategy geometric\n\n```\n\n\n\nFrom hereon, Git will use geometric repacking to optimize your objects. This should lead to less churn while ensuring that your objects are in a better-optimized state, especially in large monorepos.\n\n\n\nIn Git 2.53, we aim to make this the default strategy. So stay tuned!\n\n\n\n*This project was led by [Patrick Steinhardt](https://gitlab.com/pks-gitlab).*\n\n\n\n## New subcommand for git-repo(1) to display repository metrics\n\n\n\nPerformance of Git operations in a repository are often dependent on certain characteristics of its underlying structure. At GitLab, we host some extremely large repositories and having insight into the general structure of a repository is critical to understand performance. While it is possible to compose various Git commands and other tools together to surface certain repository metrics, Git lacks a means to surface info about a repository's shape/structure via a single command. This has led to the development of other external tools, such as [git-sizer(1)](https://github.com/github/git-sizer), to fill this gap.\n\n\n\nWith the release of Git 2.52, a new “structure” subcommand has been added to git-repo(1) with the aim to surface information about a repository's structure. Currently, it displays info about the number of references and objects in the repository in the following form:\n\n\n\n```shell\n\n$ git repo structure\n\n\n| Repository structure | Value  |\n| -------------------- | ------ |\n| * References         |        |\n|   * Count            |   1772 |\n|     * Branches       |      3 |\n|     * Tags           |   1025 |\n|     * Remotes        |    744 |\n|     * Others         |      0 |\n|                      |        |\n| * Reachable objects  |        |\n|   * Count            | 418958 |\n|     * Commits        |  87468 |\n|     * Trees          | 168866 |\n|     * Blobs          | 161632 |\n|     * Tags           |    992 |\n\n```\n\n\n\nIn subsequent releases we hope to expand on this and provide other interesting data points like the largest objects in the repository.\n\n\n\n*This project was led by [Justin Tobler](https://gitlab.com/justintobler).*\n\n\n\n## Improvements related to the Google Summer of Code 2025\n\n\n\nWe had three successful projects with the Google Summer of Code.\n\n\n\n### Refactoring in order to reduce Git's global state\n\n\n\nGit contains several global variables used throughout the codebase. This increases the complexity of the code and reduces the maintainability. As part of this project, [Ayush Chandekar](https://ayu-ch.github.io/) worked on reducing the usage of the `the_repository` global variable via a series of patches.\n\n\n\n*The project was mentored by [Christian Couder](https://gitlab.com/chriscool) and [Ghanshyam Thakkar](https://in.linkedin.com/in/ghanshyam-thakkar).*\n\n\n\n### Machine-readable Repository Information Query Tool\n\n\n\nGit lacks a centralized way to retrieve repository information, requiring users to piece it together from various commands. While `git-rev-parse(1)` has become the de-facto tool for accessing much of this information, doing so falls outside its primary purpose.\n\n\n\nAs part of this project, [Lucas Oshiro](https://lucasoshiro.github.io/en/) introduced a new command, `git-repo(1),` which will house all repository-level information. Users can now use `git repo info` to obtain repository information:\n\n\n\n```shell\n\n$ git repo info layout.bare layout.shallow object.format references.format\n\nlayout.bare=false\nlayout.shallow=false\nobject.format=sha1\nreferences.format=reftable\n\n```\n\n\n\n*The project was mentored by [Patrick Steinhardt](https://gitlab.com/pks-gitlab) and [Karthik Nayak](https://gitlab.com/knayakgl).*\n\n\n\n### Consolidate ref-related functionality into git-refs\n\n\n\nGit offers multiple commands for managing references, namely `git-for-each-ref(1)`, `git show-ref(1)`, `git-update-ref(1)`, and `git-pack-refs(1)`. This makes them harder to discover and creates overlapping functionality. To address this, we introduced the `git-refs(1)` command to consolidate these operations under a single interface. As part of this this project, [Meet Soni](https://inosmeet.github.io/) extended the command by adding the following subcommands:\n\n\n\n* `git refs optimize` to optimize the reference backend\n\n\n* `git refs list` to list all references\n\n\n* `git refs exists` to verify the existence of a reference\n\n\n\n*The project was mentored by [Patrick Steinhardt](https://gitlab.com/pks-gitlab) and [shejialuo](https://luolibrary.com/).*\n\n\n\n## What's next?\n\n\n\nReady to experience these improvements? Update to Git 2.52.0 and start using `git last-modified`.\n\n\n\nAt GitLab, we will of course ensure that all of these improvements will eventually land in a GitLab instance near you!\n\n\n\nLearn more in the [official Git 2.52.0 release notes](https://lore.kernel.org/git/xmqqh5usmvsd.fsf@gitster.g/) and explore our [complete archive of Git development coverage](https://about.gitlab.com/blog/tags/git/).\n",[24,25,23],{"featured":12,"template":13,"slug":725},"whats-new-in-git-2-52-0",{"content":727,"config":735},{"title":728,"description":729,"authors":730,"heroImage":19,"date":732,"body":733,"category":9,"tags":734},"What’s new in Git 2.51.0?","Learn about the latest contributions from GitLab's Git team and the Git community, including performance optimizations for git-push(1) and git-fetch(1).",[731],"Karthik Nayak","2025-08-18","The Git project recently released [Git 2.51](https://lore.kernel.org/git/xmqqikikk1hr.fsf@gitster.g/T/#u). Due to summer in the Northern Hemisphere and slower progress, this release cycle was on the shorter side of 8 weeks (typically a release cycle lasts about 12 weeks). Let’s look at some notable changes in this release, including contributions from the Git team at GitLab and also the wider Git community.\n\n## Performance optimizations for `git-push(1)` and `git-fetch(1)`\n\nThe `git-push(1)` and `git-fetch(1)` commands allow users to synchronize local and remote repositories. Part of the operation involves updating references in the repository. In repositories with many references, this can take significant time, especially for users who work with large development environments, monorepos, or repositories with extensive CI/CD pipelines.\nGit reference transactions can include multiple reference updates, but they follow an all-or-nothing approach. If any single update within the transaction fails, the entire transaction fails and none of the reference updates are applied. But reference updates as part of `git-push(1)` and `git-fetch(1)` are allowed to fail, which allows repositories to synchronize a subset of references even in the case where a different subset has diverged. To facilitate this behavior, Git creates a separate transaction for each reference update, allowing some transactions to fail while the rest succeed. \nCreating a separate transaction per update incurs significant overhead, as each transaction includes an initiation and teardown phase and also checks for whether there are conflicting reference names. The “reftable” backend also performs auto-compaction at the end of a transaction, so multiple transactions would trigger multiple auto-compactions, which would drastically increase the latency of the command. \nIn Git 2.51.0, these commands now use batched updates instead of separate transactions. Batched updates allow updating multiple references under a single transaction, while still allowing some updates to fail. This removes the overhead and scales better with the number of references to be updated, since only a single transaction is used. This significantly improves the performance of the “reftable” backend, which now outperforms the “files” backend. Users can reap these performance improvements without needing to make any changes.\nFor `git-fetch(1)` we see a *22x performance improvement for the “reftable” backend* and *1.25x improvement for the “files” backend* when used in a repository with 10,000 references.\n\n```text\nBenchmark 1: fetch: many refs (refformat = reftable, refcount = 10000, revision = master)\n  Time (mean ± σ):      3.403 s ±  0.775 s    [User: 1.875 s, System: 1.417 s]\n  Range (min … max):    2.454 s …  4.529 s    10 runs\n\nBenchmark 2: fetch: many refs (refformat = reftable, refcount = 10000, revision = HEAD)\n  Time (mean ± σ):     154.3 ms ±  17.6 ms    [User: 102.5 ms, System: 56.1 ms]\n  Range (min … max):   145.2 ms … 220.5 ms    18 runs\n\nSummary\n  fetch: many refs (refformat = reftable, refcount = 10000, revision = HEAD) ran\n   22.06 ± 5.62 times faster than fetch: many refs (refformat = reftable, refcount = 10000, revision = master)\n\nBenchmark 1: fetch: many refs (refformat = files, refcount = 10000, revision = master)\n  Time (mean ± σ):     605.5 ms ±   9.4 ms    [User: 117.8 ms, System: 483.3 ms]\n  Range (min … max):   595.6 ms … 621.5 ms    10 runs\n\nBenchmark 2: fetch: many refs (refformat = files, refcount = 10000, revision = HEAD)\n  Time (mean ± σ):     485.8 ms ±   4.3 ms    [User: 91.1 ms, System: 396.7 ms]\n  Range (min … max):   477.6 ms … 494.3 ms    10 runs\n\nSummary\n  fetch: many refs (refformat = files, refcount = 10000, revision = HEAD) ran\n    1.25 ± 0.02 times faster than fetch: many refs (refformat = files, refcount = 10000, revision = master)\n\n```\n\nFor `git-push(1)` we see a *18x performance improvement for the reftable backend* and *1.21x improvement for the “files” backend* when used in a repository with 10,000 references.\n\n```text\nBenchmark 1: push: many refs (refformat = reftable, refcount = 10000, revision = master)\n  Time (mean ± σ):      4.276 s ±  0.078 s    [User: 0.796 s, System: 3.318 s]\n  Range (min … max):    4.185 s …  4.430 s    10 runs\n\nBenchmark 2: push: many refs (refformat = reftable, refcount = 10000, revision = HEAD)\n  Time (mean ± σ):     235.4 ms ±   6.9 ms    [User: 75.4 ms, System: 157.3 ms]\n  Range (min … max):   228.5 ms … 254.2 ms    11 runs\n\nSummary\n  push: many refs (refformat = reftable, refcount = 10000, revision = HEAD) ran\n   18.16 ± 0.63 times faster than push: many refs (refformat = reftable, refcount = 10000, revision = master)\n\nBenchmark 1: push: many refs (refformat = files, refcount = 10000, revision = master)\n  Time (mean ± σ):      1.121 s ±  0.021 s    [User: 0.128 s, System: 0.975 s]\n  Range (min … max):    1.097 s …  1.156 s    10 runs\n\nBenchmark 2: push: many refs (refformat = files, refcount = 10000, revision = HEAD)\n  Time (mean ± σ):     927.9 ms ±  22.6 ms    [User: 99.0 ms, System: 815.2 ms]\n  Range (min … max):   903.1 ms … 978.0 ms    10 runs\n\nSummary\n  push: many refs (refformat = files, refcount = 10000, revision = HEAD) ran\n    1.21 ± 0.04 times faster than push: many refs (refformat = files, refcount = 10000, revision = master)\n\n```\n\nThis [project](https://lore.kernel.org/git/20250514-501-update-git-fetch-1-to-use-partial-transactions-v1-0-7c65f46493d4@gmail.com/) was led by [Karthik Nayak](https://gitlab.com/knayakgl).\n\n## Planning towards Git 3.0\n\n11 years ago, Git 2.0 was released, which was the last major version release of Git. While we don’t have a specific timeline for the next major Git release, this release includes decisions made towards Git 3.0.\n\nThe Git 3.0 release planning allows us to plan for and implement breaking changes and communicate them to the extended Git community. Next to documentation, Git can also be compiled with these breaking changes for those who want to experiment with these changes. More information can be found in the [BreakingChanges document](https://gitlab.com/gitlab-org/git/-/blob/master/Documentation/BreakingChanges.adoc). \n\nThe Git 2.51.0 release makes some significant changes towards Git 3.0. \n\n### Reftable as the default reference backend\n\nIn the [Git 2.45.0](https://gitlab.com/gitlab-org/git/-/blob/master/Documentation/RelNotes/2.45.0.adoc?ref_type=heads) release, the “reftable” format was introduced as a new backend for storing references like branches or tags in Git, which fixes many of the issues with the existing \"files\" backend. Please read our [beginner's guide to how reftables work](https://about.gitlab.com/blog/a-beginners-guide-to-the-git-reftable-format/) for more insight into the “reftable” backend.\n\nThe Git 2.51.0 release marks the switch to using the \"reftable\" format as default in Git 3.0 for newly created repositories and also wires up the change behind a feature flag. The “reftable” format provides the following improvements over the traditional “files” backend:\n\n* It is impossible to store two references that only differ in casing on case-insensitive filesystems with the \"files\" format. This issue is common on Windows and macOS platforms. As the \"reftable\" backend does not use filesystem paths to encode reference names this problem goes away.\n* Similarly, macOS normalizes path names that contain unicode characters, which has the consequence that you cannot store two names with unicode characters that are encoded differently with the \"files\" backend. Again, this is not an issue with the \"reftable\" backend.\n* Deleting references with the \"files\" backend requires Git to rewrite the complete \"packed-refs\" file. In large repositories with many references this file can easily be dozens of megabytes in size; in extreme cases it may be gigabytes. The \"reftable\" backend uses tombstone markers for deleted references and thus does not have to rewrite all of its data.\n* Repository housekeeping with the \"files\" backend typically performs all-into-one repacks of references. This can be quite expensive, and consequently housekeeping is a tradeoff between the number of loose references that accumulate and slow down operations that read references, and compressing those loose references into the \"packed-refs\" file. The \"reftable\" backend uses geometric compaction after every write, which amortizes costs and ensures that the backend is always in a well-maintained state.\n* Operations that write multiple references at once are not atomic with the \"files\" backend. Consequently, Git may see in-between states when it reads references while a reference transaction is in the process of being committed to disk.\n* Writing many references at once is slow with the \"files\" backend because every reference is created as a separate file. The \"reftable\" backend significantly outperforms the \"files\" backend by multiple orders of magnitude.\n* The “reftable” backend uses a binary format with prefix compression for reference names. As a result, the format uses less space compared to the \"packed-refs\" file.\n\nThis project was led by [Patrick Steinhardt](https://gitlab.com/pks-gitlab).\n\n### SHA-256 as the default hash function\n\nThe Git version control system stores objects in a content-addressable filesystem. This means it uses the hash of an object to address content such as files, directories, and revisions, unlike traditional filesystems, which use sequential numbers. Using a hash function has the following advantages: \n\n* Easy integrity checks as a single bit flip would change the hash output completely.\n* Fast object lookup as objects can be indexed by their hash.\n* Object names can be signed and third parties can trust the hash to address the signed object and all objects it references.\n* Communication using Git protocol and out of band communication methods have a short reliable string that can be used to reliably address stored content.\n\nSince its inception, Git has used the SHA-1 hashing algorithm. However, security researchers have discovered some flaws in SHA-1, specifically the [SHAttered attack](https://shattered.io), which shows a practical SHA-1 hash collision. We moved to using a hardened SHA-1 implementation by default since Git 2.13.0. However, SHA-1 is still a weak hashing algorithm and it is only a matter of time before additional attacks will further reduce its security.\n\nSHA-256 was identified as the successor to SHA-1 in late 2018. Git 2.51.0 marks it as the default hash algorithm to be used in Git 3.0.\n\nThis project was led by [brian m. carlson](https://github.com/bk2204).\n\n### Removal of `git-whatchanged(1)`\n\nThe `git-whatchanged(1)` command shows logs with differences each commit introduces. While this is now succeeded by `git log --raw`, the command was kept around for historical reasons. \n\nGit 2.51.0 requires users of the command to explicitly use the `--i-still-use-this` flag to capture any users who still use the deprecated command, and also marks the command for removal in Git 3.0. \n\nThis project was led by [Junio C Hamano](https://simple.wikipedia.org/wiki/Junio_Hamano).\n\n## `git switch` and `git restore` are no longer experimental\n\nThe `git-checkout(1)` command can be used for multiple different use cases. It can be used for switching references:\n\n```shell\n$ git status On branch master Your branch is up to date with 'origin/master'.\nnothing to commit, working tree clean\n$ git checkout next Switched to branch 'next' Your branch is up to date with 'origin/next'.\n```\n\nOr for restoring files:\n\n```shell\n$ echo \"additional line\" >> git.c\n$ git status On branch master Your branch is up to date with 'origin/master’.\nChanges not staged for commit:\n  (use \"git add \u003Cfile>...\" to update what will be committed)\n  (use \"git restore \u003Cfile>...\" to discard changes in working directory)\n    modified:   git.c\n\nno changes added to commit (use \"git add\" and/or \"git commit -a\")\n$ git checkout git.c Updated 1 path from the index\n$ git status On branch master Your branch is up to date with 'origin/master’.\nnothing to commit, working tree clean\n```\n\nFor new users of Git, this can cause a lot of confusion. So in Git 2.33.0, these were split into two new commands, `git-switch(1)` and `git-restore(1)`.\nThe `git-switch(1)` command allows users to switch to a specific branch: \n\n```shell\n$ git status On branch master Your branch is up to date with 'origin/master'.\nnothing to commit, working tree clean\n$ git switch next Switched to branch 'next' Your branch is up to date with 'origin/next'.\n```\n\nAnd the `git-restore(1)` command allows users to restore working tree files: \n\n```shell\n$ echo \"additional line\" >> git.c\n$ git status On branch master Your branch is up to date with 'origin/master’.\nChanges not staged for commit:\n  (use \"git add \u003Cfile>...\" to update what will be committed)\n  (use \"git restore \u003Cfile>...\" to discard changes in working directory)\n    modified:   git.c\n\nno changes added to commit (use \"git add\" and/or \"git commit -a\")\n$ git restore git.c\n$ git status On branch master Your branch is up to date with 'origin/master’.\nnothing to commit, working tree clean\n```\n\nWhile the two commands have existed since 2019, they were marked as experimental. The effect is that the Git project doesn’t guarantee backwards compatibility for those commands: the behavior may change at any point in time. While the intent originally was to stabilize those commands after a couple of releases, this hasn’t happened up to this point.\nThis has led to several discussions on the Git mailing list where users are unsure whether they can start using these new commands, or whether they might eventually go away again. But given that no significant changes have ever been proposed, and that some users are already using these commands, we have decided to no longer declare them as experimental in Git 2.51.\nThis project was led by [Justin Tobler](https://gitlab.com/justintobler).\n\n## `git for-each-ref(1)` receives pagination support\n\nThe `git for-each-ref` command is used to list all references present in the repository. As it is part of the plumbing layer of Git, this command is frequently used for example by hosting forges to list references that exist in the repository in their UI. But as repositories grow, it becomes less realistic to list all references at once – after all, the largest repositories may contain millions of them! So instead, forges tend to paginate the references.\n\nThis surfaces an important gap: `git-for-each-ref` does not know to skip references from previous pages that have already been shown. Consequently, it may have to list a large number of uninteresting references before it finally starts to yield the references required for the current page. This is inefficient and leads to higher-than-necessary latency or even timeouts.\n\nGit 2.51.0 supports a new `--start-after` flag for `git for-each-ref`, which allows paginating the output. This can also be combined with the `--count` flag to iterate over a batch of references. \n\n```shell\n$ git for-each-ref --count=10 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-001 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-002 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-003 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-004 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-005 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-006 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-007 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-008 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-009 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-010\n$ git for-each-ref --count=10 --start-after=refs/heads/branch-010 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-011 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-012 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-013 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-014 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-015 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-016 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-017 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-018 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-019 9751243fba48b34d29aabfc9784803617a806e81 commit    refs/heads/branch-020\n```\n\nThis project was led by [Karthik Nayak](https://gitlab.com/knayakgl).\n\n## What's next?\n\nReady to experience these improvements? Update to Git 2.51.0 and start using `git switch` and `git restore` in your daily workflow. \n\nFor GitLab users, these performance enhancements will automatically improve your development experience once your Git version is updated.\n\nLearn more in the [official Git 2.51.0 release notes](https://lore.kernel.org/git/xmqqikikk1hr.fsf@gitster.g/T/#u) and explore our [complete archive of Git development coverage](https://about.gitlab.com/blog/tags/git/).\n",[25,24,23],{"featured":30,"template":13,"slug":736},"what-s-new-in-git-2-51-0",{"promotions":738},[739,753,765],{"id":740,"categories":741,"header":743,"text":744,"button":745,"image":750},"ai-modernization",[742],"ai-ml","Is AI achieving its promise at scale?","Quiz will take 5 minutes or less",{"text":746,"config":747},"Get your AI maturity score",{"href":748,"dataGaName":749,"dataGaLocation":241},"/assessments/ai-modernization-assessment/","modernization assessment",{"config":751},{"src":752},"https://res.cloudinary.com/about-gitlab-com/image/upload/v1772138786/qix0m7kwnd8x2fh1zq49.png",{"id":754,"categories":755,"header":757,"text":744,"button":758,"image":762},"devops-modernization",[756,556],"product","Are you just managing tools or shipping innovation?",{"text":759,"config":760},"Get your DevOps maturity score",{"href":761,"dataGaName":749,"dataGaLocation":241},"/assessments/devops-modernization-assessment/",{"config":763},{"src":764},"https://res.cloudinary.com/about-gitlab-com/image/upload/v1772138785/eg818fmakweyuznttgid.png",{"id":766,"categories":767,"header":769,"text":744,"button":770,"image":774},"security-modernization",[768],"security","Are you trading speed for security?",{"text":771,"config":772},"Get your security maturity score",{"href":773,"dataGaName":749,"dataGaLocation":241},"/assessments/security-modernization-assessment/",{"config":775},{"src":776},"https://res.cloudinary.com/about-gitlab-com/image/upload/v1772138786/p4pbqd9nnjejg5ds6mdk.png",{"header":778,"blurb":779,"button":780,"secondaryButton":785},"Start building faster today","See what your team can do with the intelligent orchestration platform for DevSecOps.\n",{"text":781,"config":782},"Get your free trial",{"href":783,"dataGaName":48,"dataGaLocation":784},"https://gitlab.com/-/trial_registrations/new?glm_content=default-saas-trial&glm_source=about.gitlab.com/","feature",{"text":492,"config":786},{"href":52,"dataGaName":53,"dataGaLocation":784},1772652087511]