Furgit#

Furgit is a fast Git library in pure Go (and a little bit of optional Go Assembly).

Project status#

• Initial development
• Poor code quality
• Frequent breaking changes
• Do not use in production
• Will likely use Semantic Versioning 2.0.0 later

Current features#

• SHA-256 and SHA-1
  (runtime supports both; tests are SHA-256 by default, but the sha1 build tag makes it test SHA-1)
• Reading loose objects
• Writing loose objects
• Reading packfiles
  • Delta resolution
• Writing packfiles
  • Delta compression
  • Thin packs
• Reading commit-graph's
• General support for blobs, trees, commits, and tags

Future features#

• Compression algorithm agility
• Multi pack indexes
• Repack
• Better delta base selection strategy
• Delta reuse; delta islands
• Reading reachability bitmaps
• Writing reachability bitmaps when writing packfiles
• commit-graph (in progress)
• Network protocols
• Reftables
• Large object promisors?
• Large binary database format or something
• And much more

General goals#

Furgit intends to be a general-purpose Git library.

For now, Furgit primarily prioritize APIs and optimizations that are likely to be used by software development forges and other server-side usages; in particular, Furgit follows the needs of Villosa and to some extent tangled.

Performance optimizations#

• Aggressive pooling of byte buffers
• Aggressive pooling of custom zlib readers
• Minor SIMD optimizations for Adler-32
• Memory-mapping packfiles and their indexes

Performance#

See gitbench for details on methods.

All tests below were run on linux.git with HEAD at 6da43bbeb6918164 on a Intel(R) Core(TM) i5-10210U CPU @ 1.60GHz.

Note: go-git is expected to perform much better after storage: filesystem/mmap, Add PackScanner to handle large repos.

Architectural considerations#

Furgit heavily relies on memory mappings of packfiles, and assume relatively predictable fault handling behavior. In distributed systems, we advise not using Furgit on top of distributed network filesystems such as CephFS or NFS; consider solutions where redundancy and distributions belong above the Git layer, e.g., using an RPC protocol over a set of Git nodes each running Furgit on local repositories.

Dependencies#

• The standard library
• Some things from golang.org/x
• github.com/cespare/xxhash/v2 (may move in-tree at some point)

Some external code is also introduced and maintained in-tree.

Environment requirements#

A standard UNIX-like filesystem with syscall.Mmap is expected.

Repos and mirrors#

• Codeberg (with the canonical issue tracker)
• SourceHut mirror
• tangled mirror
• GitHub mirror

Community#

• #lindenii on irc.runxiyu.org
• #lindenii on Libera.Chat

History and lineage#

• I wrote Lindenii Forge
• I wrote hare-git
• I wanted a faster Git library for Lindenii Villosa the next generation of Lindenii Forge
• I translated hare-git and put it into internal/common/git in Villosa
• I extracted it out into a general-purpose library, which is what we have now
• I was thinking of names and I accidentally typed "git" as "fur" (i.e., left shifted one key on my QWERTY keyboard), so, "Furgit"

License#

This project is licensed under the GNU Affero General Public License, Version 3.0 only.

Pursuant to Section 14 of the GNU Affero General Public License, Version 3.0, Runxi Yu is hereby designated as the proxy who is authorized to issue a public statement accepting any future version of the GNU Affero General Public License for use with this Program.

Therefore, notwithstanding the specification that this Program is licensed under the GNU Affero General Public License, Version 3.0 only, a public acceptance by the Designated Proxy of any subsequent version of the GNU Affero General Public License shall permanently authorize the use of that accepted version for this Program.

For the purposes of the Developer Certificate of Origin, the "open source license" refers to the GNU Affero General Public License, Version 3.0, with the above proxy designation pursuant to Section 14.

All contributors are required to "sign-off" their commits (using git commit -s) to indicate that they have agreed to the Developer Certificate of Origin, reproduced below.

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.