Understanding Distributed SourceControl

About Me

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• Lorna Jane Mitchell

• http://lornajane.net

• PHP Consultant/Developer

• Open Source project lead http://joind.in

• Occasional writer/speaker

• Twitter: @lornajane

Source Control

The Aims of Source Control

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• Central keeping-place

The Aims of Source Control

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• Central keeping-place

• History of changes

The Aims of Source Control

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• Central keeping-place

• History of changes

• Painless collaboration

Traditional Centralised Source Control

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• One repository (repo)

• Working copies

• Mature

• Simple

• Tools:

• CVS

• Subversion http://subversion.apache.org/

Traditional Centralised Source Control

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repo

checkout checkoutcheckout

Subversion

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Recommended centralised solution

Project is now an Apache Software Foundation project. From the missionstatement:

Subversion exists to be universally recognized and adopted as anopen-source, centralized version control system characterized by its

reliability as a safe haven for valuable data; the simplicity of its model andusage; and its ability to support the needs of a wide variety of users and

projects, from individuals to large-scale enterprise operations.

http://lwn.net/Articles/381794/

Centralised Branching Strategies

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There are a few common patterns when branching:

• Version branches

• Feature branches

• Live branch

Code Merging with Centralised Systems

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• Make changes

• Update

• Commit

• Merge happens on central repo

• Can be slow

Distributed Source Control

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• Many repos

• Local repo

• Tools (all with comparable features)

• Git http://git-scm.com/

• Mercurial http://mercurial.selenic.com/

• Bazaar http://bazaar.canonical.com/

• Powerful/complex

Distributed Source Control

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repo

repo reporepo repo

Distributed Source Control

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repo

repo

repo

repo

repo

The Biggest Change

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FAST

Snapshots vs Changesets

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A revision number describes a set of patches. Not a state of code.

With distributed version control, the distributed part is actually not themost interesting part. The interesting part is that these systems think in

terms of changes, not in terms of versions

http://www.joelonsoftware.com/items/2010/03/17.html

Branching on Distributed Systems

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• Can branch any repo

• Branches can be private

Branching on Distributed Systems

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• Can branch any repo

• Branches can be private

• Merge commits from other branches on local repo

Working with Branches: Creating

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$ git branch api

$ git branchapi

* master

$ git checkout apiSwitched to branch 'api'

$ git branch

* apimaster

Working with Branches: Using

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$ mkdir api$ vim api/index.php$ git add api/

$ git commit -m "added the web service"[api 62582e1] added the web service

1 files changed, 4 insertions(+), 0 deletions(-)create mode 100644 api/index.php

$ lsapiwebsite

Working with Branches: Switching

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$ git checkout masterSwitched to branch 'master'

$ lswebsite

Multiple Repositories

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remote repo

main repo

local

Timelines

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• Commits keep their timestamps

• They show at the time they were commited

• To a repo

• Not when they were merged to this one

• Tools help illustrate

Timelines: git log –oneline

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be81f69 Merge branch 'master' of git://github.com/joindi n/joind.ina67dabb Merge commit 'fentie/issue91'526039d Merge commit 'jaytaph/JOINDIN-38-2'0bc1a57 merge of hatfieldje/feature/JOINDIN-100d3c7195 Added slide icon to talk-list983d1a0 Fixed dates in CfP display and talk add/edit4edf8be Merge commit 'justincarmony/JOINDIN-97'bec3ac1 Moving the settings from the method to the Controlle r's members01d3feb Admins can approve other admins31ba4c1 Added counter to Event Claims linkce2e46b Updated README. Includes instructions for enablin g RewriteEnginece356d5 Corrected session type dropbox9c2f645 Merge commit 'justincarmony/74-howto-block'0ce1551 Merge remote-tracking branch 'jaytaph/JOINDIN-1 04'

Timelines: git log –graph –oneline

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* be81f69 Merge branch 'master' of git://github.com/joindi n/joind.in|\| * a67dabb Merge commit 'fentie/issue91'| |\| | * 2b229ef IDE removing extra EOL whitespace| | * 82b3aa7 switching to single empty test instead of !isset and false| | * b03d6df adding check to ensure speakers cannot rate their ow n talks| * | 526039d Merge commit 'jaytaph/JOINDIN-38-2'| |\ \| | * | 01d3feb Admins can approve other admins| | * | 31ba4c1 Added counter to Event Claims link| * | | 0bc1a57 merge of hatfieldje/feature/JOINDIN-100| |\ \ \| | * | | 983d1a0 Fixed dates in CfP display and talk add/edit| | * | | 0ddfd83 JOINDIN-100| | * | | d00e1f3 feature/JOINDIN-100| | * | | f5a5775 feature/JOINDIN-100| * | | | d3c7195 Added slide icon to talk-list

Products and Supporting Tools

GUI Tools

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Most OS/DVCS combinations covered

• IDE plugins

• Versions on OS X for SVN

• Tower on OS X for git

• Tortoise* for Windows users

• git and windows not recommended

• CLI on every platform

Bridging the Gap

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Bridges: local DVCS functionality with centralised repos

Tools:

• git-svn

• bzr-svn

• hg-git

• and more

Supporting Distributed Workflows

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Need to keep track of:

• Commits on other repos

• Relationships between repos

• Patches (pull requests)

Supporting Distributed Workflows

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Need to keep track of:

• Commits on other repos

• Relationships between repos

• Patches (pull requests)

Often: source browsing, documentation and issue trackers are alsoincluded

Collaboration Sites

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• Git

• Github http://github.com/

• Gitorious http://gitorious.org/

• Mercurial

• Bitbucket http://bitbucket.org/

• Bazaar

• Launchpad http://launchpad.net/

Also Sourceforge who support all of the above and more http://sf.net

Understanding Distributed Source Control

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• Differences from centralised systems

• Tools

• Gotchas

Questions?

Thanks!

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• Slides: http://slideshare.net/lornajane

• Twitter: @lornajane

• Web: http://lornajane.net/