Version control with Subversion

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Version Control with Subversion

PLUG Linux Users [email protected]

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Subversion

In the world of open-source software, the Concurrent Versions System (CVS) was the tool of choice for version control for manyyears.

Subversion is similar to CVS, but it avoids most of CVS noticeable flaws.

The most common use for Subversion is to track changes to source code. But Subversion can be used to manage changes to any sort of information—images, music, databases, documentation, and so on. To Subversion, all data is just data.

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What is Subversion?

Subversion is a free/open-source version control system. Subversion manages files and directories, and the changes made to them, over time. This allows you to recover older versions of your data, or examine the history of how your data changed.Fosters Collaboration.Mistakes can be undone.Is NOT a Software Configuration Management system. Version control of any data, perhaps your telephone bills. ?

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Subversion provides

Directory versioning.True version history.Atomic commitsVersioned metadata.Choice of Network Layers.Consistent Data Handling.Efficient Branching and TaggingHackablity

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Fundamental ConceptsThe Repository

Repository is kind of a file server.

What makes it special is that it remembers every change ever written to it: every change to every file, and even changes to the directory tree itself, such as the addition, deletion, and rearrangement of files and directories. When a client reads data from the repository, it normally sees only the latest version of the filesystem tree. But the client also has the ability to view previous states of the filesystem. For example, a client can ask historical questions like, “What did this directory contain last Wednesday?”

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Fundamental Concepts:Versioning Models

The problem of file sharing: Problem to Avoid!

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Fundamental Concepts: Versioning Models:

The Lock-Modify-Unlock Solution

In this Model, Repository allows only one person to change at a time.Locking may cause Administrative ProblemsLocking may cause unnecessary serialization.Locking may create a false sense of security.

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Fundamental Concepts: Versioning Models:

The Copy-Modify-Merge Solution

In this model, each user's client contacts the project repository and creates a personal working copy—a local reflection of the repository's files and directories. Users then work simultaneously and independently, modifying their private copies. Finally, the private copies are merged together into a new, final version.The version control system often assists with the merging, but ultimately a human being is responsible for making it happen correctly.

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Fundamental Concepts: Versioning Models:

The Copy-Modify-Merge Solution

Figure 1: Figure 2:

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Fundamental Concepts: Versioning Models:

The Copy-Modify-Merge Solution

What if changes do overlap? This situation is called a conflict, and it's usually not much of a problem When Harry asks his client to merge the latest repository changes into his working copy, his copy of file A is somehow flagged as being in a state of conflict: he'll be able to see both sets of conflicting changes, and manually choose between them. Note that software can't automatically resolve conflicts; only humans are capable of understanding and making the necessary intelligent choices. Once Harry has manually resolved the overlapping changes—perhaps after a discussion with Sally—he can safely save the merged file back to the repository.

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Fundamental Concepts: Versioning Models:

The Copy-Modify-Merge Solution

The copy-modify-merge model may sound a bit chaotic, but in practice, it runs extremely smoothly. Users can work in parallel, never waiting for one another When they work on the same files, it turns out that most of their concurrent changes don't overlap at all; conflicts are infrequent. And the amount of time it takes to resolve conflicts is usually far less than the time lost by a locking system. In the end, it all comes down to one critical factor: user communication. When users communicate poorly, both syntactic and semantic conflicts increase. No system can force users to communicate perfectly, and no system can detect semantic conflicts

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Fundamental Concepts:

Subversion in Action.Subversion Repository URLs.

svn checkout http://svn.example.com:9834/repos svn checkout file:///path/to/repos

Working Copies.

.svn directory in the working copy contains administrative files.

To get a working copy, you checkout from the repository:

$ svn checkout http://svn.example.com/repos/calcA calc/MakefileA calc/integer.cA calc/button.c

Checked out revision 56. $ ls -A calc Makefile integer.c button.c .svn/

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Fundamental Concepts:

Subversion in ActionThe act of publishing your changes is more commonly known as committing (or checking in) changes to the repository. $svn commit filename –m “log”#collaborator will do:#svn update$svn commit operation publishes changes to the any number of files and directories as a single atomic transaction.

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Fundamental Concepts:

Subversion in ActionRepository Structure.Single Global Revision.Unlike most version control systems, Subversion's revision numbers apply to entire trees, not individual files

The Repository

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Fundamental Concepts:

Subversion in Action

Inside .svn directory keeps track as files working revision and timestamp of update.Unchanged, and Current.Locally Changed, and Current.Unchanged and Out of dateLocally Changed and Out of date.

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Basic Usage

Getting data into Repository – svn importRecommended Repository layout.

/trunk/branches/tags

Initial checkout: svn checkout repopath

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Basic Work Cycle

Update your woking copy.svn update

Make changes.svn addsvn deletesvn copysvn move

Examine your changessvn statussvn diff

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Basic Work Cycle

Possibly undo some changes.svn revert

Resolve Conflicts ( Merge others changes)svn updatesvn resolved

Commit your changes.svn commit

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Examining History

svn logsvn diffsvn catsvn listsvn cleanup

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Revision Specifiers

HEADThe latest (or “youngest”) revision in the repository.

BASE The revision number of an item in a working copy. If the item has been locally modified, the “BASE version” refers to the way the item appears without those local modifications

COMMITTED The most recent revision prior to, or equal to, BASE, in which an item changed.

PREV The revision immediately before the last revision in which an item changed. Technically, this boils down to COMMITTED-1.

Revision Dates

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Properties

In addition to versioning your directories and files, Subversion provides interfaces for adding, modifying, and removing versioned metadata on each of your versioned directories and files. We refer to this metadata as properties.Custom revision properties are also frequently used. One common such use is a property whose value contains an issue tracker ID with which the revision is associated, perhaps because the change made in that revision fixes a bug filed in the tracker issue with that ID.

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Property setting

svn propset license -F /path/to/LICENSE calc/button.c property 'license' set on 'calc/button.c' svn:eol-stylesvn:executablesvn:keywordssvn:mime-type

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Keyword substitution

Subversion has the ability to substitute keywords—pieces of useful, dynamic information about a versioned file—into the contents of the file itself Date, Revision, Author, HeadURL, IdSet the svn:keyword property of any of the above Use the $Date$, $Author$ notation in the versioned file. The values will get automatically substituted.

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Locking

Locking concept supported by svn.

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Branching and Merging

Branches are svn copy operation on the Repository.

Branches of Development

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Branching and MergingStart point

After Branching

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Best practises of merging

Tracking Changes Manually.Previewing merges.Noticing and ignoring ancestryMerges and MovesCreating a Tag, same as Branch

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SVN Server configuration

Svnserve ServerSvnserve over sshThe Apache HTTP server

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Comparision of the Repositories

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That’s all Folks

Lundblad is a leading contributor to the Subversion open source code project, which has produced a widely implemented code management system. He was among five leaders of open source code recognized in August at the O'Reilly Open Source Conference. Unlike the others, Lundblad is blind. Amazing!