scalar: add a README with a roadmap
The Scalar command will be contributed incrementally, over a bunch of patch series. Let's document what Scalar is about, and then describe the patch series that are planned. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Johannes Schindelin committed
Dec 3, 2021 at 13:34 UTC
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+# Scalar - an opinionated repository management tool
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+
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+Scalar is an add-on to Git that helps users take advantage of advanced
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+performance features in Git. Originally implemented in C# using .NET Core,
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+based on the learnings from the VFS for Git project, most of the techniques
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+developed by the Scalar project have been integrated into core Git already:
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+
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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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+
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+This directory contains the remaining parts of Scalar that are not (yet) in
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+core Git.
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+
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+## Roadmap
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+
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+The idea is to populate this directory via incremental patch series and
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+eventually move to a top-level directory next to `gitk-git/` and to `git-gui/`. The
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+current plan involves the following patch series:
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+
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+- `scalar-the-beginning`: The initial patch series which sets up
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+ `contrib/scalar/` and populates it with a minimal `scalar` command that
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+ demonstrates the fundamental ideas.
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+
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+- `scalar-c-and-C`: The `scalar` command learns about two options that can be
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+ specified before the command, `-c <key>=<value>` and `-C <directory>`.
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+
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+- `scalar-diagnose`: The `scalar` command is taught the `diagnose` subcommand.
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+
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+- `scalar-and-builtin-fsmonitor`: The built-in FSMonitor is enabled in `scalar
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+ register` and in `scalar clone`, for an enormous performance boost when
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+ working in large worktrees. This patch series necessarily depends on Jeff
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+ Hostetler's FSMonitor patch series to be integrated into Git.
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+
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+- `scalar-gentler-config-locking`: Scalar enlistments are registered in the
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+ user's Git config. This usually does not represent any problem because it is
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+ rare for a user to register an enlistment. However, in Scalar's functional
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+ tests, Scalar enlistments are created galore, and in parallel, which can lead
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+ to lock contention. This patch series works around that problem by re-trying
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+ to lock the config file in a gentle fashion.
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+
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+- `scalar-extra-docs`: Add some extensive documentation that has been written
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+ in the original Scalar project (all subject to discussion, of course).
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+
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+- `optionally-install-scalar`: Now that Scalar is feature (and documentation)
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+ complete and is verified in CI builds, let's offer to install it.
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+
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+- `move-scalar-to-toplevel`: Now that Scalar is complete, let's move it next to
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+ `gitk-git/` and to `git-gui/`, making it a top-level command.
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+
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+The following two patch series exist in Microsoft's fork of Git and are
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+publicly available. There is no current plan to upstream them, not because I
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+want to withhold these patches, but because I don't think the Git community is
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+interested in these patches.
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+
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+There are some interesting ideas there, but the implementation is too specific
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+to Azure Repos and/or VFS for Git to be of much help in general (and also: my
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+colleagues tried to upstream some patches already and the enthusiasm for
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+integrating things related to Azure Repos and VFS for Git can be summarized in
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+very, very few words).
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+
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+These still exist mainly because the GVFS protocol is what Azure Repos has
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+instead of partial clone, while Git is focused on improving partial clone:
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+
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+- `scalar-with-gvfs`: The primary purpose of this patch series is to support
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+ existing Scalar users whose repositories are hosted in Azure Repos (which
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+ does not support Git's partial clones, but supports its predecessor, the GVFS
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+ protocol, which is used by Scalar to emulate the partial clone).
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+
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+ Since the GVFS protocol will never be supported by core Git, this patch
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+ series will remain in Microsoft's fork of Git.
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+
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+- `run-scalar-functional-tests`: The Scalar project developed a quite
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+ comprehensive set of integration tests (or, "Functional Tests"). They are the
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+ sole remaining part of the original C#-based Scalar project, and this patch
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+ adds a GitHub workflow that runs them all.
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+
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+ Since the tests partially depend on features that are only provided in the
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+ `scalar-with-gvfs` patch series, this patch cannot be upstreamed.