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