Version Control Systems

1
Version Control Systems

• Version Control System enables different
  programmers to work on concurrently on a set of
  files or directories.
• VCS system helps us to track the changes made by
  these developers.
• These systems very helpful to merge the works of
  these developers into a single work.
• They can help us to restore all of the old
  versions of files and directories.

2
Why We Need VCS?

• Data Integrity Old revisions in repositories
• Productivity Integrating the work of multiple
  developers
• Accountability Who has made the modifications
  and when
• Branching Old versions need to be supported
  while new version is going on. Merge changes from
  one branch to another.
• Record Keeping Logs about all the changes made
  in project can be helpful.

3
Why We Need VCS?

• Distribution of Work Version control can make
  dealing with distributed development easier, by
  automating much of the workload of exchanging and
  merging the work of different developers.
• Rapid Development Codes in repositories can be
  useful for other projects.

4
Basic Elements of VCS

• The Repository Directory structure on a server
  with each versioned file stored separately.
• Working Directory Checkout from repositories
  copy of projects from repositories allows us
  editing, testing changes during development
  process. (commit, update)
• Revisions The history of changes to the project
  over time.
• Log On commit, update, merge, delete ... a
  message to log what change is made.

5
Basic Elements of VCS

• Tagging Frees developers from such as revision
  numbers or dates. It is easy to go back at a
  later date to search out the cause of a bug.
• Branching Each branch can be worked on
  independently, and changes committed to one
  branch will not affect any other branches of the
  project.
• Locking The developer locks a versioned file
  when beginning to make changes. While the file is
  locked, no other developer will be allowed to
  make any changes.

6
Subversion(SVN)

• The core of Subversion is a set of libraries with
  a well-documented open API.
• This API allows developers to write custom
  clients for Subversion, integrate it into another
  tool, provide a GUI.
• Subversion has much larger feature set and
  commands.

7
Features Of Subversion

• Subversion uses client-server architecture
• Central repository on server and clients check
  out local working copies.
• We can modify anything on working copies then
  changes between repository and working copy
  merged. Modified version is committed to the
  repository.
• Repository Flexibility You can move, rename, and
  copy files and directories as much as you like
  without any worry that you will lose your history
  or corrupt older revisions.

8
Atomic Commits

• Atomic Commits Subversion uses transactions
  whenever it modifies the database.
• When a commit starts, Subversion marks the
  current state of the database, then makes its
  modifications.
• If a crash interrupts the commit, there is no
  risk that the database will be corrupted.

9
Cheap Copies

• When a developer uses the svn copy command,
  Subversion does not make a copy of data contained
  in those files.
• It just marks the location of the new file and
  links it back to the history of the original
  file, up to the point where the copy is made.
• If changes are applied to the copy, a new path of
  revision is created for the copy,independent of
  subsequent revisions applied to the original file.

10
Binary Files

• CVS doesnt store differences to versioned binary
  files. Instead, it just stores an entire new copy
  of the file whenever a binary file is committed.
• Subversion improves on this by using a binary
  difference function for all files, which allows
  binary files to be versioned the same as text
  files.
• Subversion provides complete copies of both
  versions of the file, which allows the user to
  easily use an external editor to manually merge
  the conflicted file.

11
Storage and Network Protocol

• The Subversion storage uses individual files for
  each revision in the repository.
• When you commit revision 3529, there will be a
  file named 3529 created, which holds all of the
  changes for that revision.
• SVN-specific network protocol that requires a
  dedicated server and open port.
• Served over HTTP via Apache, there is no need to
  open a special port on the server.

12
Data Transfer

• It only transfers file differences both from
  client to server and from server to client unlike
  CVS.
• It stores a full copy of the working directory
  from the last update, to allow the user to make
  comparisons with local changes without contacting
  the server.

13
Limitations Of Subversion

• Locking Subversion currently has no support for
  file locking to prevent more than one person from
  working on a particular file at a given point in
  time.
• Distributed Repository Subversion does not
  currently have any support for distributed
  repositories, but there is a secondary project,
  called SVK.
• Merge History and Visualization Problem ???

14
SVN, Subclipse Installation And References

• http//www.blendedtechnologies.com/setting-up-subv
  ersion-on-ubuntu/11
• http//subclipse.tigris.org/install.html
• Using The Subversion Version Control System in
  Development Projects William Nagel