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66 lines
2.9 KiB
66 lines
2.9 KiB
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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