<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 there are also 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,
so the information here
might be biased in favor of Fossil. Ask around with people who have
used both Fossil and Git for other opinions.
¹<small><i>Git does not support
wiki, tickets, or tech-notes, so those elements will not transfer when
exporting from Fossil to Git.</i></small>
<h2>2.0 Executive Summary:</h2>
<blockquote><center><table border=1 cellpadding=5>
<tr><th width="50%">GIT</th><th width="50%">FOSSIL</th></tr>
<tr><td>File versioning only</td>
<td>Versioning, Tickets, Wiki, and Technotes</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 development</td>
<td>Designed for SQLite development</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></center></blockquote>
<h2>3.0 Discussion</h2>
<h3>3.1 Feature Set</h3>
Git provides file versioning services only, whereas Fossil adds an
integrated [./wikitheory.wiki | wiki],
[./bugtheory.wiki | ticketing & bug tracking],
[./embeddeddoc.wiki | embedded documentation], and
[./event.wiki | Technical notes].
These additional capabilities are available for Git as 3rd-party and/or
user-installed 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 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.
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 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>3.2 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 their SHA1 hash.
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 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>3.3 Cathedral vs. Bazaar</h3>
Fossil and Git promote different development styles. Git promotes a
"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 the their
low-friction path.
Git encourages a style in which individual developers work in relative
isolation, maintaining their
own branches and the 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>3.4 Linux vs. SQLite</h3>
Git was specifically designed to support the development of Linux.
Fossil was specifically designed to support the development of SQLite.
Both SQLite and Linux are important pieces of software.
SQLite is found on far more systems than Linux. (Almost every Linux
system uses SQLite, but there are many non-Linux systems such as
iPhones, PlayStations, and Windows PC that use SQLite.) On the other
hand, for those systems that do use Linux, Linux is a far more important
component.
Linux uses a bazaar-style development model. There are thousands and
thousands of contributors, most of whom do not know each others names.
Git is designed for this scenario.
SQLite uses cathedral-style development. 95% of the code in SQLite
comes from just three programmers, 64% from just the lead developer.
And all SQLite developers know each other well and interact daily.
Fossil is designed for this development model.
<h3>3.5 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 on $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>3.6 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 inseperable.
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.
<h3>3.7 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>3.8 GPL vs. BSD</h3>
Git is covered by the GPL license whereas Fossil is covered by
a two-clause BSD license.
Consider the difference between GPL and BSD licenses: GPL is designed
to make writing easier at the expense of making reading harder. BSD is
designed to make reading easier and the expense of making writing harder.
To a first approximation, the GPL license grants the right to read
source code to anyone who promises to give back enhancements. In other
words, the act of reading GPL source code (a prerequiste for making changes)
implies acceptance of the license which requires updates to be contributed
back under the same license. (The details are more complex, but the
foregoing captures the essence of the idea.) A big advantage of the GPL
is that anybody can contribute to the code without having to sign additional
legal documentation because they have implied their acceptance of the GPL
license by the very act of reading the source code. This means that a GPL
project can legally accept anonymous and drive-by patches.
The BSD licenses, on the other hand, make reading much easier than the GPL,
because the reader need not surrender proprietary interest
in their own enhancements. On the flip side, BSD and similarly licensed
projects must obtain legal affidavits from authors before
new content can be added into the project. Anonymous and drive-by
patches cannot be accepted. This makes signing up new contributors for
BSD licensed projects harder.
The licenses on the implementations of Git and Fossil only apply to the
implementations themselves, not to the projects which the systems store.
Nevertheless, one can see a more GPL-oriented world-view in Git and a
more BSD-oriented world-view in Fossil. Git encourages anonymous contributions
and siloed development, which are hallmarks of the GPL/bazaar approach to
software, whereas Fossil encourages a more tightly collaborative,
cliquish, cathedral-style approach more typical of BSD-licensed projects.
<h2>4.0 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>4.1 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, and Tech-Notes</b>
Git only provides versioning of source code. Fossil strives to provide
other related configuration 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 status" 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.
<h2>4.2 Features found in Git but missing from Fossil</h2>
* <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 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.