4 Scalar is a repository management tool that optimizes Git for use in large
5 repositories. It accomplishes this by helping users to take advantage of
6 advanced performance features in Git. Unlike most other Git built-in commands,
7 Scalar is not executed as a subcommand of 'git'; rather, it is built as a
8 separate executable containing its own series of subcommands.
13 Scalar was originally designed as an add-on to Git and implemented as a .NET
14 Core application. It was created based on the learnings from the VFS for Git
15 project (another application aimed at improving the experience of working with
16 large repositories). As part of its initial implementation, Scalar relied on
17 custom features in the Microsoft fork of Git that have since been integrated
23 * sparse checkout (cone mode),
24 * scheduled background maintenance,
27 With the requisite Git functionality in place and a desire to bring the benefits
28 of Scalar to the larger Git community, the Scalar application itself was ported
29 from C# to C and integrated upstream.
34 Scalar is comprised of two major pieces of functionality: automatically
35 configuring built-in Git performance features and managing repository
38 The Git performance features configured by Scalar (see "Background" for
39 examples) confer substantial performance benefits to large repositories, but are
40 either too experimental to enable for all of Git yet, or only benefit large
41 repositories. As new features are introduced, Scalar should be updated
42 accordingly to incorporate them. This will prevent the tool from becoming stale
43 while also providing a path for more easily bringing features to the appropriate
46 Enlistments are how Scalar knows which repositories on a user's system should
47 utilize Scalar-configured features. This allows it to update performance
48 settings when new ones are added to the tool, as well as centrally manage
49 repository maintenance. The enlistment structure - a root directory with a
50 `src/` subdirectory containing the cloned repository itself - is designed to
51 encourage users to route build outputs outside of the repository to avoid the
52 performance-limiting overhead of ignoring those files in Git.
57 Scalar is implemented in C and interacts with Git via a mix of child process
58 invocations of Git and direct usage of `libgit.a`. Internally, it is structured
59 much like other built-ins with subcommands (e.g., `git stash`), containing a
60 `cmd_<subcommand>()` function for each subcommand, routed through a `cmd_main()`
61 function. Most options are unique to each subcommand, with `scalar` respecting
62 some "global" `git` options (e.g., `-c` and `-C`).
64 Because `scalar` is not invoked as a Git subcommand (like `git scalar`), it is
65 built and installed as its own executable in the `bin/` directory, alongside
66 `git`, `git-gui`, etc.