A proposed Subversion vision and roadmap

Last week, five of Subversion's developers -- myself, Hyrum Wright (who
helped me author this lengthy mail), Greg Stein, Stefan Sperling, and Karl
Fogel ("we", henceforth) -- met in New York City to evaluate Subversion's
current trajectory as a project and to jointly develop suggestions for any
course correction deemed necessary.  The unfortunate impetus for the meeting
was feedback from representatives of some very large installations of
Subversion that, from where they sat, the Subversion project was stagnating.
 This is a somewhat fair assertion.  It's not that the community is or has
ever been in danger of doing nothing.  But even when we march in step
towards a goal, we don't do a good job of communicating outwardly about that
fact, leading to the appearance of inactivity.  And lately, our ongoing
efforts have been less like a team of folks working in concert towards a
common vision, and more like the individual piddlings common to mature open
source software.

Make no mistake:  Subversion is mature open source software.  It works well
for open source projects and -- in one of the biggest software coups of the
last decade -- we've found that it's also good enough to supplant other
well-established version control systems, open-source or otherwise, inside
the highly structured walls of the enterprise.  Unfortunately, "good enough"
still leaves the enterprise user base frustrated at the most inopportune
times (like, say, when managing branches near releases).  And if you judge
success by mindshare, it's now clear the DVCS tools have rendered our "good
enough" somewhat obsolete when it comes to serving many open source
projects, even.

VISION

Subversion has no future as a DVCS tool.  Let's just get that out there.  At
least two very successful such tools exist already, and to squeeze another
horse into that race would be a poor investment of energy and talent.
What's more, huge classes of users remain categorically opposed to the very
tenets on which the DVCS systems are based.  They need centralization.  They
need control.  They need meaningful path-based authorization.  They need
simplicity.  In short, they desperately need Subversion.  It's this class of
user -- the corporate developer -- that stands to benefit hugely from what
Subversion brings to the party.  And it's that class of user which we
believe Subversion should cater to, ideally without ostracizing the open
source volunteers who remain our largest source of development investment.

Corporate developers come in all shapes and sizes, from self-administering
10-person teams to geographically-distributed organizations of thousands of
developers on hundreds of teams serviced by dedicated IT departments.
Subversion can't be all things to all people, but it can be a well-defined
subset of things to most people.  It shouldn't sacrifice its trademark
simplicity when growing the features most likely to be used in large-scale
deployments; it shouldn't optimize for the large enterprise in a way that
will alienate the long tail composed of much smaller deployments.  By
defining the subset of things Subversion is and those it is not, we
recognize our own boundaries and prevent years of wandering through the
proverbial wilderness of feature creep.

Someone wiser than I once said, "Where there is no vision, the people
perish."  So recognizing the benefits that Subversion already offers, and
projecting a bit into the future what we'd like to see Subversion become, we
offer the following vision statement for your review:

   Subversion exists to be universally recognized and adopted as an
   open-source, centralized version control system characterized by its
   reliability as a safe haven for valuable data; the simplicity of its
   model and usage; and its ability to support the needs of a wide variety
   of users and projects, from individuals to large-scale enterprise
   operations.

A shorter, business-card-sized motto (offered as a replacement to the
obsolete "A compelling replacement for CVS") might be:  "Enterprise-class
centralized version control for the masses".

ROADMAP

With that vision in mind, we identified a number of high-value improvements
which Subversion should gain in coming releases.  Then we took a casual pass
at assigning some technical "plumbing" dependencies for each of these.
Here's what we came up with, in the form "FEATURE: [DEPENDENCY ...]", where
"FS-NG" = major FS backend overhaul, "WC-NG" = WC-NG, and "Ev2" = svn_editor_t:

    * Obliterate:  FS-NG
    * Shelve/Checkpoint:  WC-NG
    * Repository-dictated Configuration:  WC-NG (?)
    * Rename Tracking:  WC-NG, Ev2, FS-NG (?)
    * Improved Merging:  WC-NG
    * Improved Tree Conflict Handling:  WC-NG, Ev2, Rename Tracking
    * Enterprise Authentication Mechanisms:
    * Forward History Searching:  FS-NG (?)
    * Log Message Templates:  Repository-dictated Configuration

By examining this dependency chain, factoring in the development momentum
which will exist around WC-NG, and admitting that some of the major plumbing
overhauls not currently underway may prove to be just as costly as the WC-NG
work (if not more so), we believe that the following feature roadmap is one
which will serve Subversion users well:

   1.7: WC-NG; HTTPv2; 'svn patch'; typical slew of various bug fixes

   1.8: repository-dictated configuration; tree conflicts improvements;
        WC-NG-enabled stuff (rename tracking, compressed pristines,
        shelving/checkpointing, ...)

   1.9: Editor v2 (for server->client rename handling improvements)

   [...]

   2.0: FS-NG (ideally a parallelized task), with some (to-be-identified)
        FS-NG enabled features.

That last item is likely to be contentious, so it bears explaining.  We
believe that our current two filesystem offerings are stifling innovation.
On the one hand we have the BDB backend which is a breeze to develop for but
is only occasional used; on the other is the far-more-popular FSFS backend
whose fundamental principles so constrain the system as to destroy much hope
of serious design overhaul; and in the middle lies the feature parity
requirement we've been living under thus far which binds Subversion to the
union of the two backends' weaknesses.  We confidently assert that to break
system-wide compatibility with a so-called 2.0 release will be Subversion's
great overall detriment, both from the perspective of efficient use of
development energy and in user adoption.  So we propose that an
as-yet-fictional Subversion 2.0 be allowed to break compatibility with the
1.x line only in ways which can be mitigated using the RA layer as a
compatibility shim.  Additionally, we believe that merely releasing a 2.0
with a new FS backend but without new user-visible features enabled by that
overhaul will be ill-received.

COMMUNITY

We also discussed matters of communication and community.  Subversion has
historically had a very tight-knit community of developers, and we've
provided a resource for communicating with users through the various mailing
lists.  With the increase in corporate involvement, and the changing roles
(and employers!) of committers, the Subversion ecosystem can at times seems
a bit fractured.  To an enterprise manager responsible for thousands of
users, and millions of dollars of investment, and billions of bytes of data,
this fracturing appears as a liability when considering an investment in
Subversion.  Most corporations understand the open source nature of
Subversion's development method (indeed, this very thing has driven
Subversion adoption), but they still want a unified face when it comes to
communication, planning, and project feedback.

One proposed solution is a Subversion "planet", to be hosted at a
re-purposed subversion.org.  The planet would aggregate feeds from
individual contributors, as well as the various corporate entities
interested in Subversion development.  While various commercial interests
(CollabNet, WANdisco, elego, etc.) may compete in some areas, they are all
committed to improving Subversion as a whole.  Enterprise users need to see
this unity across Subversion's corporate sponsors, and a communication
stream which interleaves these corporate voices works toward that end.

Whatever the solution, we need a defined plan which we then communicate to
the end users and customers who are deploying Subversion installations.

But communication alone isn't enough.  We need to find ways to grow our
developer community itself.  Attendance at the recent Subversion Corporation
Annual Members Meeting was low (by design and recommendation, of course),
but a startling realization was made there.  When the agenda item for voting
new full committers into membership was on the table, there were no
candidates.  Think about that:  no new full committers for Subversion in the
past year.  This is a bad thing.  We need to find a way to embrace and
empower would-be Subversion contributors.  Telling them to troll through the
issue tracker looking for bite-sized issues is not the way to do that -- it
communicates "we can't be bothered to mentor you".  When somebody wants to
start making contributions, our community must recognize the value of that
contributor and mentor him or her toward full committership, for the good of
that contributor and of the community.  Further, our public roadmap needs to
highlight the items that we really wish we could be working on but lack the
manpower to handle.  This would provide those looking for ways to accelerate
Subversion's roadmap with some cues for doing that in harmony with the Big
Picture.

SUMMARY

I've covered a lot of ground here, but decisions in this community have
always been and will be made on this mailing list, and they deserve to be
made with as much information as possible.  You now know where a small
contingent of developers stand on these issues.  I'd like to publicize on
our project website a *community-endorsed* vision and roadmap ASAP, and then
get to the business of moving Subversion forward along those lines.

So what say you?

-- C-Mike, for the NYC conference attendees

-- 
C. Michael Pilato <cmpilato@collab.net>
CollabNet   <>   www.collab.net   <>   Distributed Development On Demand