Subversion in a distributed world

Subversion in a Distributed World

About Me
Lorna Mitchell
PHP Developer/Trainer/Consultant at Ibuildings
Host of Dutch PHP Conference 2010
Active with PHPWomen.org
Organiser at PHPNW
Personal blog: http://lornajane.net
Twitter: @lornajane

Source Control
Keeping-place for code
Centralised or distributed
Project archive
Collaboration tool
Integration point
for development
for business processes

One True Way

The Products

Subversion (svn) Creator CollabNet URL Maintainer Apache Users PHP Sourceforge FreeBSD Apache Software Foundation License Apache/BSD style Documentation Excellent, more mature Red Bean Book

Subversion: The Roapmap
Taken from:
http://lwn.net/Articles/381794/
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.

Git Creator Linus Torvalds URL Maintainer Junio Hamano Users Linux kernel Ruby on Rails CakePHP Debian GNOME License GPL Documentation "terse", a lot of documentation for an unfamiliar system

Bazaar (bzr) Creator Martin Pool URL Maintainer Canonical Users Ubuntu MySQL Inkscape Squid License GPL Documentation Excellent! Aimed at beginners, UI designed to be intuitive

Mercurial (hg) Creator Matt Mackall URL Maintainer Matt Mackall Users Mozilla OpenOffice.org SymbianOS NetBeans License GPL Documentation Good, online book and command line help

Features
Atomic commits
File renames
Symbolic links
Pre/Post event hooks
Merge tracking
Tags
EOL conversions

Protocols
Everything supports SSH and HTTP(S)
Distributed systems support email
Bazaar supports FTP
Git supports rsync

Centralised vs Distributed Source Control

Centralised Source Control

Centralised Source Control
Traditional model
Subversion uses this
Other products can do it

Distributed Source Control

Distributed Source Control
Git, Bazaar and Mercurial are distributed
Many repositories
Move changes between any or all of these

Revisions vs Changes
From a Joel Spolsky post:
With distributed version control, the distributed part is actually not the most interesting part. The interesting part is that these systems think in terms of changes, not in terms of versions

Repo Structure: SVN
Top level projects
Branches, tags and trunk
Can check out and commit at subdirectory level

Repo Structure: DVCS
Separate repository per project
Can only check out the whole thing
Controlled at the top level
Can safely copy directories :)

Referring to Revisions
svn: whole repo increments with every change
git: generates a SHA1, a 40 character hexadecimal string
bzr: uses per branch incrementing revision numbers
hg: sequential revision number AND unique changeset ID in a SHA1

Git Hashing
Every commit has an identifying hash
Hash is of commit and includes information about parent
Any change in any version is seen later, because parental hashes change
Ensures consistency

Hashing: Branch 1 commit 69540cd8d2dda61424982d388976c2b3c95d4278 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:56:03 2010 +0100 fixes coding standards compatibility commit 482fc8d3de1b523c6aa44d0f0a6b97ced9273499 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:51:53 2010 +0100 creating the hello world file

Hashing: Branch 2 commit 24ab6108e42f7662cf32c14e0e707c5534dec47c Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:55:14 2010 +0100 extends greeting to universe commit 67681edee47744780010ecf9e085c0f097a32e11 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:54:36 2010 +0100 formalises world greeting commit 482fc8d3de1b523c6aa44d0f0a6b97ced9273499 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:51:53 2010 +0100 creating the hello world file

Hashing: Merged Changes commit baa58ead49d46ac10d360e9d83fd6603c0f57061 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:56:03 2010 +0100 fixes coding standards compatibility commit 24ab6108e42f7662cf32c14e0e707c5534dec47c Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:55:14 2010 +0100 extends greeting to universe commit 67681edee47744780010ecf9e085c0f097a32e11 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:54:36 2010 +0100 formalises world greeting commit 482fc8d3de1b523c6aa44d0f0a6b97ced9273499 Author: Lorna <lorna@lornajane.net> Date: Sat Apr 17 20:51:53 2010 +0100 creating the hello world file

http://www.flickr.com/photos/bensonkua/2543171151/ Cherry Picking

Cherry Picking Example $ git fetch origin remote: Counting objects: 5, done. remote: Compressing objects: 100% (2/2), done. remote: Total 3 (delta 0), reused 0 (delta 0) Unpacking objects: 100% (3/3), done. From /home/lorna/git_examples2/../git_examples 482fc8d..69540cd master -> origin/master $ git cherry-pick 69540cd8d2dda61424982d388976c2b3c95d4278

http://www.flickr.com/photos/_heiko/1907664495/ Local is FAST

Local Repo: Advantages
Its FAST
Can see and diff against history while offline
Commit offline, then share these later

Building Bridges
Bridge between SVN repo and local
bzr-svn https://launchpad.net/bzr-svn
git-svn http://www.kernel.org/pub/software/scm/git/docs/git-svn.html
Local distributed-style repo
Communicates with central SVN server
Pulls complete history
diff, log fast and offline
Work offline, commit later

bzr-svn: Setting the Scene
Subversion repository
Standard svn checkout in subversion/
Bzr checkout in /lorna-repo/lorna-trunk
Branch of this in /lorna-repo/lorna-branch

bzr-svn: Adding Content with Bzr $ bzr commit -m "initialising database files and hello.php" Committing to: /home/lorna/.../lorna-repo/lorna-branch/ added db added hello.php added db/setup.sql Committed revision 2. $ bzr log ------------------------------------------------------------ revno: 2 committer: Lorna Mitchell <lorna@lornajane.net> branch nick: lorna-branch timestamp: Sun 2010-04-25 14:46:44 +0100 message: initialising database files and hello.php ------------------------------------------------------------ revno: 1 svn revno: 578 (on /lorna-test) committer: lorna timestamp: Sun 2010-04-25 12:02:32 +0000 message: New project for some source control examples

bzr-svn: Sending Changes to SVN $ bzr push ../lorna-trunk/ All changes applied successfully. Pushed up to revision 2. $ cd ../../subversion $ svn log --------------------------------------------------------------------- r579 | lorna | 2010-04-25 14:46:23 +0100 (Sun, 25 Apr 2010) | 1 line initialising database files and hello.php --------------------------------------------------------------------- r578 | lorna | 2010-04-25 14:02:32 +0100 (Sun, 25 Apr 2010) | 3 lines New project for some source control examples ---------------------------------------------------------------------

Changing State of the Landscape
Talk proposed October 2009
Accepted December 2009
Immature tools the deal-breaker
Written March 2010
Tools now usable, and improving

Web Accessible
All these tools are web browseable
Either natively or easily

Trac
Trac now has integration for all these mentioned
Can hook in to update track from commits
Trac provides code browsing and understands source control

http://www.flickr.com/photos/rhk313/2741140421/ Tortoise

Tortoise
TortoiseSVN - widely used windows gui
http://tortoisesvn.tigris.org/
TortoiseBzr
https://launchpad.net/tortoisebzr
TortoiseGit
http://code.google.com/p/tortoisegit/
TortoiseHg
http://tortoisehg.bitbucket.org/

Code Hosting and Collaboration
Provide repository space
Repo browsing, linked projects
Forums and mailing lists
Wiki (or similar: launchpad has blueprints)
Publish downloadable versions
Message other collaborators

Code Hosting Providers GitHub http://github.com/ git Bitbucket http://bitbucket.org/ hg Google Code http://code.google.com/ svn, hg Launchpad https://launchpad.net/ bzr SourceForge http://sourceforge.net/ svn, bzr, hg, git (and cvs)

Making Choices

Distributed Development
Multiple repositories
Distribution is foreign to corporations
Processes are as important as tools
Learning curve

My Development Process
Based on Subversion
Needs process on top of tools to use the best bits in a distributed setup
Single repo
All branches are available and shared
Everything is visible and backed up

Permissions
SVN has very granular access control
Can use any of apache's mechanisms
Can path-restrict read access
Access control for DVCS mostly use hooks
What about access to cloned/forked repositories?

Cost of Transition
Steeper learning curve
Implementation costs
tool migration
process changes
supporting tool migration
user training (ongoing!)
Hype and dismissive attitudes are unhelpful

A Read-only SVN Copy
Common workaround
Read-only suversion repo
Holds latest changes on a nominated git repo
Tools can hook in
Users can svn:external to it

In My World
Subversion has its place
mature
great documentation and ecosystem
simple!
What about managers, junior devs, designers, contractors?

One Recommendation

Team and Project
Global team of expert geeks - use DCVS (any one)
Colocated team of mixed ability - use SVN
Everything else is a sliding scale!
Consider
Your people
Your admins
The documentation, support and community of your chosen solution

Choice

Thanks!
http://joind.in/1598

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Subversion in a distributed world

by Lorna Mitchell

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