Feb 2011

DVCS with Mercurial

Agenda What is DVCS? How does it work? Mercurial features Extensions Why not SVN? (SVN vs Mercurial) Questions

What is DVCS?

What is DVCS? DVCS - A distributed revision control,

distributed version control system (DVCS) keeps track of software revisions and allows many developers to work on a given project independent of network access or a central server. Committing, branching and merging are fast.

DVCS is…Distributed version control system (DVCS) takes a peer-to-peer approach, as opposed to the client-server approach of centralized systems. Rather than a single, central repository on which clients synchronize, each peer's working copy of the codebase is a bona-fide repository. Distributed version control conducts synchronization by exchanging patches (change-sets) from peer to peer

Currently in SVN

Currently in Mercurial

DVCS - Advantages Fast

Mercurials implementation and data structures are designed to be fast. You can generate diffs between revisions, or jump back in time within seconds.

Platform independentMercurial was written with platform independence in mind. Therefore most of Mercurial is written in Python, with a small part in portable C for performance reasons. As a result, binary releases are available on all major platforms.

ExtensibleThe functionality of Mercurial can be increased with extensions, either by activating the official ones which are shipped with Mercurial or downloading some from the wiki or by writing your own. Extensions are written in Python and can change the workings of the basic commands, add new commands and access all the core functions of Mercurial.

Open SourceMercurial is free software licensed under the terms of the GNU General Public License Version 2.

How does it work?or how it works with TortoiseHG

You have:

A working copy. The files you are currently editing. A repository. A directory (.hg in Mercurial) containing all patches and metadata (comments,

guids, dates, etc.). There’s no central server so the data stays with you.

How does it work? – Merge

How does it work? – Changesets! Like in Subversion, history consists of a number of

commits. They're called changesets in Mercurial. A changeset is an atomic collection of changes to files in

a repository. It contains all recorded local files modification and:

information about who made the change (the "committer"), why ("comments") and when (date/time, timezone)

the name of the branch ("default", if omitted or not set) A changeset is identified uniquely by a changeset ID

(1ef7872431f9c64908c732f0bcd4db5700b4cb70 ). In a single repository, you can identify it using a revision number.

How does it work? – Csets tree!

How does it work? – Csets tree!

How does it work? – Push to stable!

How does it work? – Push to stable!

How does it work? – Push to stable!

Mercurial featuresPushing changes to another repositoryMerging conflicting changesSearching through historyViewing repository through a web browserUsing Mercurial as a “super client” for

Subversion

Mercurial Features – Merge conflicts

Mercurial Features – Merge conflicts

Mercurial Features – web browser

How does it work? - basic commands Commit selected diffs in checked files. Undo (rollback) last immediate commit. Visual Diff checked files. Revert checked files to last revisioned state Add checked files Move checked files Remove checked files Forget checked files Pull all changes from another repository into the current

one Push all changes from your repository into another one Shelve changes when they not needed and get them

back in future

Extensions

Extensions - Enabling

Extensions - rebase

Extensions – Shelve

The shelve extension lets you to choose which parts of the changes in a working directory you'd like to set aside temporarily, at the granularity of patch hunks. You can later restore the shelved patch hunks using the unshelve command.

Extensions – more and more Purge – deletes all files and directories in the

repository that are not being tracked by Mercurial Notify – Send email to subscribed addresses to

notify repository changes Convert – convert repositories from other SCMs

into Mercurial Highlight – Highlight syntax in the file revision

view of hgweb Bisect – Quickly find the revision that introduces

a bug or feature bisecting the history tree …

Why not SVN?

SVN Limitations

Branching is easy, merging is easy

If your computer is on, you have access to the repository

Sharing changes withselected people is easy (hg serve/hg push/hg pull)

Aware of file history and can merge into renamed file Single .hg directory at root of

source tree Fast performance; you’re working

on local filesystem Cheap to create/throw away local

experimental branch

Branching is easy, but merging is painful

Active net connectionrequired to interact

Unable to share changeswith others without sharing with everyone (including the build server)

Fails to merge changes whensomething is renamed

.svn files are littered throughout your source tree

Slow over-the-wire performance

Discourages experimentation

DVCS/Mercurial Strengths

SVN Strengths DVCS/Mercurial limitations

Most developers will need to learn to think differently

Better understanding of version control concepts required

Need to define and adhere to convention to know where the trunk is

Familiar to most developers

Relatively easy to grasp

Everyone knows where the trunk is because there’s only one server

Projects using mercurial1. Mozilla2. OpenJDK3. OpenSolaris4. OpenOffice.org5. Symbian OS6. Adium7. Audacious8. Coin3D9. OSSEC10. CubicWeb11. Dovecot IMAP server12. GeeXboX13. RabbitMQ14. Go programming language15. GNU Octave16. GNU Multi-Precision Library

17. Growl18. LEMON19. LinuxTV/Video4Linux20. LuxRender 3D Render Engine21. Mercurial22. MoinMoin wiki software23. Mutt24. Netbeans25. Nuxeo26. Ogre3D27. SAGE28. Vim29. Lugaru HD30. Tryton31. Tuenti

Usefull links

Download Mercurial: http://mercurial.selenic.com/wiki/Download

Dvcs With Mercurial presentation: http://www.slideshare.net/tednaleid/dvcs-with-mercurial-no-notes

Migrating from and VCS: http://mercurial.selenic.com/wiki/RepositoryConversion

VS Plugin: http://visualhg.codeplex.com/ Mercurial as a “super client” for Subversion:

http://naleid.com/blog/2008/05/01/using-mercurial-as-a-super-client-for-subversion/

Questions?