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