<title>Fossil Versus Git</title>
<h2>1.0 Don't Stress!</h2>
If you start out using one DVCS and later decide you like the other better,
you can easily [./inout.wiki | move your content].¹
Fossil and [http://git-scm.com | Git] are very similar in many respects,
but they also have important differences.
See the table below for
a high-level summary and the text that follows for more details.
Keep in mind that you are reading this on a Fossil website, and though
we try to be fair, the information here
might be biased in favor of Fossil. Ask around for second opinions from
people who have used <em>both</em> Fossil and Git.
¹<small><i>Git does not include a
wiki, a ticket tracker, a forum, or a tech-note feature, so those elements will not transfer when
exporting from Fossil to Git. GitHub adds some of these to stock Git,
but because they're not part of Git proper, [./mirrortogithub.md|exporting a Fossil
repository to GitHub] will still not include them; Fossil tickets do not
become GitHub issues, for example.</i></small>
<h2>2.0 Differences Between Fossil And Git</h2>
Differences between Fossil and Git are summarized by the following table,
with further description in the text that follows.
<blockquote><table border=1 cellpadding=5 align=center>
<tr><th width="50%">GIT</th><th width="50%">FOSSIL</th></tr>
<tr><td>File versioning only</td>
<td>Versioning, Tickets, Wiki, Technotes, Forum</td></tr>
<tr><td>Ad-hoc pile-of-files key/value database</td>
<td>Relational SQL database</td></tr>
<tr><td>Bazaar-style development</td><td>Cathedral-style development</td></tr>
<tr><td>Designed for Linux kernel development</td>
<td>Designed for SQLite development</td></tr>
<tr><td>Focus on individual branches</td>
<td>Focus on the entire tree of changes</td></tr>
<tr><td>Lots of little tools</td><td>Stand-alone executable</td></tr>
<tr><td>One check-out per repository</td>
<td>Many check-outs per repository</td></tr>
<tr><td>Remembers what you should have done</td>
<td>Remembers what you actually did</td></tr>
<tr><td>GPL</td><td>BSD</td></tr>
</table></blockquote>
<h3>2.1 Feature Set</h3>
Git provides file versioning services only, whereas Fossil adds
integrated [./wikitheory.wiki | wiki],
[./bugtheory.wiki | ticketing & bug tracking],
[./embeddeddoc.wiki | embedded documentation],
[./event.wiki | technical notes], and a [./forum.wiki | forum].
These additional capabilities are available for Git as 3rd-party
add-ons, but with Fossil they are integrated into
the design. One way to describe Fossil is that it is
"[https://github.com/ | GitHub]-in-a-box."
If you clone [https://github.com/git/git|Git's self-hosting repository],
you get just Git's source code.
If you clone Fossil's self-hosting repository, you get the entire
Fossil website — source code, documentation, ticket history, and so forth.
That means you get a copy of this very article and all of its historical
versions, plus the same for all of the other public content on this site.
For developers who choose to self-host projects (rather than using a
3rd-party service such as GitHub) Fossil is much easier to set up, since
the stand-alone Fossil executable together with a [./server.wiki#cgi|2-line CGI script]
suffice to instantiate a full-featured developer website. To accomplish
the same using Git requires locating, installing, configuring, integrating,
and managing a wide assortment of separate tools. Standing up a developer
website using Fossil can be done in minutes, whereas doing the same using
Git requires hours or days.
<h3>2.2 Database</h3>
The baseline data structures for Fossil and Git are the same, modulo
formatting details. Both systems store check-ins as immutable
objects referencing their immediate ancestors and named by a
cryptographic hash of the check-in content.
The difference is that Git stores its objects as individual files
in the ".git" folder or compressed into
bespoke "pack-files," whereas Fossil stores its objects in a
relational ([https://www.sqlite.org/|SQLite]) database file. To put it
another way, Git uses an ad-hoc pile-of-files key/value database whereas
Fossil uses a proven, general-purpose SQL database. This
difference is more than an implementation detail. It
has important consequences.
With Git, one can easily locate the ancestors of a particular check-in
by following the pointers embedded in the check-in object, but it is
difficult to go the other direction and locate the descendants of a
check-in. It is so difficult, in fact, that neither native Git nor
GitHub provide this capability. With Git, if you are looking at some
historical check-in then you cannot ask
"What came next?" or "What are the children of this check-in?"
Fossil, on the other hand, parses essential information about check-ins
(parents, children, committers, comments, files changed, etc.)
into a relational database that can be easily
queried using concise SQL statements to find both ancestors and
descendents of a check-in.
Leaf check-ins in Git that lack a "ref" become "detached," making them
difficult to locate and subject to garbage collection. This
"detached head" problem has caused untold grief for countless
Git users. With Fossil, all check-ins are easily located using
a variety of attributes (parents, children, committer, date, full-text
search of the check-in comment) and so detached heads are simply not possible.
The ease with which check-ins can be located and queried in Fossil
has resulted in a huge variety of reports and status screens
([./webpage-ex.md|examples]) that show project state
in ways that help developers
maintain enhanced awareness and comprehension
and avoid errors.
<h3>2.3 Cathedral vs. Bazaar</h3>
Fossil and Git promote different development styles. Git promotes a
"[https://en.wikipedia.org/wiki/The_Cathedral_and_the_Bazaar|bazaar]"
development style in which numerous anonymous developers make
small and sometimes haphazard contributions. Fossil
promotes a "cathedral" development model in which the project is
closely supervised by an highly engaged architect and implemented by
a clique of developers.
Nota Bene: This is not to say that Git cannot be used for cathedral-style
development or that Fossil cannot be used for bazaar-style development.
They can be. But those modes are not their design intent nor their
low-friction path.
Git encourages a style in which individual developers work in relative
isolation, maintaining their
own branches and occasionally rebasing and pushing selected changes up
to the main repository. Developers using Git often have their own
private branches that nobody else ever sees. Work becomes siloed.
This is exactly what one wants when doing bazaar-style development.
Fossil, in contrast, strives to keep all changes from all contributors
mirrored in the main repository (in separate branches) at all times.
Work in progress from one developer is readily visible to all other
developers and to the project leader, well before the code is ready
to integrate. Fossil places a lot of emphasis on reporting the state
of the project, and the changes underway by all developers, so that
all developers and especially the project leader can maintain a better
mental picture of what is happening, and better situational awareness.
<h3>2.4 Linux vs. SQLite</h3>
Git was specifically designed to support the development of the Linux kernel.
Fossil was specifically designed to support the development of SQLite.
SQLite is much more widely deployed than the Linux kernel, but for
Linux-based systems, the kernel is the more fundamental component.
Although both projects must rank high on any objective list of "most
important [https://en.wikipedia.org/wiki/Free_and_open-source_software|FOSS]
projects," the two projects are almost entirely unlike
one another, and this shows up in the design choices of the tools
created to support them.
The Linux kernel uses a bazaar-style development model. There are thousands and
thousands of contributors, most of whom do not know each others names.
These thousands are responsible for producing roughly 89⨉ more code than
is in SQLite. (10.7
[https://en.wikipedia.org/wiki/Source_lines_of_code|MLOC] vs 0.12 MLOC
according to [https://dwheeler.com/sloccount/|SLOCCount].) Git is
designed for this scenario.
SQLite uses cathedral-style development. 95% of the code in SQLite
comes from just four programmers, and 64% of it is from the lead developer alone.
The SQLite developers know each other well and interact daily.
Fossil is designed for this development model.
We think you should ask yourself whether you have
[https://en.wikipedia.org/wiki/Linus_Torvalds|Linus Torvalds] scale
software configuration management problems or
[https://en.wikipedia.org/wiki/D._Richard_Hipp|D. Richard Hipp] scale
problems when choosing your DVCS. An
[https://en.wikipedia.org/wiki/Impact_wrench|impact wrench]
is not the best tool for hanging a picture on the living room wall.
<h3>2.5 Individual Branches vs. The Entire Change History</h3>
Both Fossil and Git store history as a directed acyclic graph (DAG)
of changes, but Git tends to focus more on individual branches of
the DAG, whereas Fossil puts more emphasis on the entire DAG.
For example, the default "sync" behavior in Git is to only sync
a single branch, whereas with Fossil the only sync option it to
sync the entire DAG. Git commands,
GitHub, and GitLab tend to show only a single branch at
a time, whereas Fossil usually shows all parallel branches at
once. Git has commands like "rebase" that help keep all relevant
changes on a single branch, whereas Fossil encourages a style of
many concurrent branches constantly springing into existance,
undergoing active development in parallel for a few days or weeks, then
merging back into the main line and disappearing.
This difference in emphasis arises from the different purposes of
the two systems. Git focuses on individual branches, because that
is exactly what you want for a highly-distributed bazaar-style project
such as Linux. Linus Torvalds does not want to see every check-in
by every contributor to Linux, as such extreme visibility does not scale
well. But Fossil was written for the cathedral-style SQLite project
with just a handful of active committers. Seeing all
changes on all branches all at once helps keep the whole team
up-to-date with what everybody else is doing, resulting in a more
tightly focused and cohesive implementation.
<h3>2.6 Lots of little tools vs. Self-contained system</h3>
Git consists of many small tools, each doing one small part of the job,
which can be recombined (by experts) to perform powerful operations.
Git has a lot of complexity and many dependencies and requires an "installer"
script or program to get it running.
Fossil is a single self-contained stand-alone executable with hardly
any dependencies. Fossil can be (and often is) run inside a
minimally configured chroot jail. To install Fossil,
one merely puts the executable somewhere in the $PATH.
The designer of Git says that the Unix philosophy is to have lots of
small tools that collaborate to get the job done. The designer of
Fossil says that the Unix philosophy is "It just works." Both
individuals have written their DVCSes to reflect their own view
of the "Unix philosophy."
<h3>2.7 One vs. Many Check-outs per Repository</h3>
A "repository" in Git is a pile-of-files in the ".git" subdirectory
of a single check-out. The check-out and the repository are located
together in the filesystem.
With Fossil, a "repository" is a single SQLite database file
that can be stored anywhere. There
can be multiple active check-outs from the same repository, perhaps
open on different branches or on different snapshots of the same branch.
Long-running tests or builds can be running in one check-out while
changes are being committed in another.
Git version 2.5 adds a feature to emulate Fossil's decoupling of the
repository from the check-out tree, which it calls
"[https://git-scm.com/docs/git-worktree|git-worktree]." This command
sets up a series of links in the filesystem to
allow a single repository to host multiple check-outs. However,
the interface is sufficiently difficult to use that most people
find it easier to create a separate clone for each check-out.
There are also practical consequences of the way it's implemented
that make worktrees not quite equivalent to the main Git repo + checkout
tree.
With Fossil, the complete decoupling of repository and check-out tree
means every working check-out tree is treated equally. It's common in
Fossil to have a check-out tree for each major working branch so that
you can switch branches with a "cd" command rather than replace the
current working file set with a different file set by updating in place,
as Git prefers.
<h3>2.8 What you should have done vs. What you actually did</h3>
Git puts a lot of emphasis on maintaining
a "clean" check-in history. Extraneous and experimental branches by
individual developers often never make it into the main repository. And
branches are often rebased before being pushed, to make
it appear as if development had been linear. Git strives to record what
the development of a project should have looked like had there been no
mistakes.
Fossil, in contrast, puts more emphasis on recording exactly what happened,
including all of the messy errors, dead-ends, experimental branches, and
so forth. One might argue that this
makes the history of a Fossil project "messy." But another point of view
is that this makes the history "accurate." In actual practice, the
superior reporting tools available in Fossil mean that the added "mess"
is not a factor.
One commentator has mused that Git records history according to
the victors, whereas Fossil records history as it actually happened.
<h3>2.9 GPL vs. BSD</h3>
Git is covered by the GPL license, whereas Fossil is covered by
[https://fossil-scm.org/fossil/file/COPYRIGHT-BSD2.txt|a two-clause BSD
style license]. It is not our purpose here to try to persuade you to make
the same choice of license that we did. Neither license affects the
managed repository contents. However, we do believe the choice of
license affected the design and implementation of these two DVCSes,
which may affect your choice when deciding which one you'd rather use.
The GPL allows a project to do without a
[https://en.wikipedia.org/wiki/Contributor_License_Agreement|constributor
license agreement] (CLA) because by the very act of distributing
binaries, you are bound to also distribute the source under a compatible
license. There are GPL-based projects that do require a CLA, but this is
usually done to further commercial interests rather than to maintain
the legal integrity of the
[https://en.wikipedia.org/wiki/Free_and_open-source_software|FOSS]
project itself.
Contrast a BSD-style project, where contributions are not automatically
relicensed merely by being distributed with the preexisting BSD code.
Such projects often require a CLA even when there are no corporate
interests, to ensure
that all contributions are compatibly licensed with the existing body of
code. It's a way to add a "no takebacks" clause to the basic BSD
license.
A CLA makes signing up new contributors harder. It's an extra
gatekeeping step, so it discourages low-engagement contributors. A CLA
also drives off those unable to accept the CLA's restrictions on their
rights, which are otherwise quite minimal under a BSD-style license. The
GPL requires much the same sort of relinquishment of rights without this
up-front gatekeeping.
We think this additional friction is not an entirely bad thing. We think
it improves contributor community cohesion, because everyone who
pushed past that legal friction made an affirmative, active step to get
into the community.
These differences in world-view show up in the design and implementation
of these two DVCSes.
Git encourages anonymous contributions
and siloed development, which are hallmarks of the GPL/bazaar approach to
software, whereas Fossil encourages a more tightly collaborative
cathedral-style approach more typical of BSD-licensed projects.
<h2>3.0 Missing Features</h2>
Most of the capabilities found in Git are also available in Fossil and
the other way around. For example, both systems have local check-outs,
remote repositories, push/pull/sync, bisect capabilities, and a "stash."
Both systems store project history as a directed acyclic graph (DAG)
of immutable check-in objects.
But there are a few capabilities in one system that are missing from the
other.
<h3>3.1 Features found in Fossil but missing from Git</h3>
* <b>The ability to show descendents of a check-in.</b>
Both Git and Fossil can easily find the ancestors of a check-in. But
only Fossil shows the descendents. (It is possible to find the
descendents of a check-in in Git using the log, but that is sufficiently
difficult that nobody ever actually does it.)
* <b>Wiki, Embedded documentation, Trouble-tickets, Tech-Notes, and Forum</b>
Git only provides versioning of source code. Fossil strives to provide
other related project management services as well.
* <b>Named branches</b>
Branches in Fossil have persistent names that are propagated
to collaborators via [/help?cmd=push|push] and [/help?cmd=pull|pull].
All developers see the same name on the same branch. Git, in contrast,
uses only local branch names, so developers working on the
same project can (and frequently do) use a different name for the
same branch.
* <b>The [/help?cmd=all|fossil all] command</b>
Fossil keeps track of all repositories and check-outs and allows
operations over all of them with a single command. For example, in
Fossil is possible to request a pull of all repositories on a laptop
from their respective servers, prior to taking the laptop off network.
Or it is possible to do "fossil all changes" to see if there are any
uncommitted changes that were overlooked prior to the end of the workday.
* <b>The [/help?cmd=ui|fossil ui] command</b>
Fossil supports an integrated web interface. Some of the same features
are available using third-party add-ons for Git, but they do not provide
nearly as many features and they are not nearly as convenient to use.
<h3>3.2 Features found in Git but missing from Fossil</h3>
* <b>Rebase</b>
Because of its emphasis on recording history exactly as it happened,
rather than as we would have liked it to happen, Fossil deliberately
does not provide a "rebase" command. One can rebase manually in Fossil,
with sufficient perserverence, but it is not something that can be done with
a single command.
* <b>Push or pull a single branch</b>
The [/help?cmd=push|fossil push], [/help?cmd=pull|fossil pull], and
[/help?cmd=sync|fossil sync] commands do not provide the capability to
push or pull individual branches. Pushing and pulling in Fossil is
all or nothing. This is in keeping with Fossil's emphasis on maintaining
a complete record and on sharing everything between all developers.