Version Control

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Version Control

• Using the Subversion Version Control System in
  Development Projects
• William Nagel

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Sample Disorganized Project

• Hey, Jane, could you send me a copy of those
  changes you made last Tuesday?
• Bob, this function doesnt work anymore. Did
  you change something?
• Sorry, I cant seem to find those old classes.
  I guess youll just have to re-implement them.
• OK, weve all been working hard for the last
  week. Now lets integrate everyones work
  together.

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What is version control?

• Basic functionality
• keep track of changes made to files (allows
  roll-backs)
• merge the contributions of multiple developers
• Benefits
• facilitates backups
• increased productivity (vs manual version
  control)
• encourages experimentation
• helps to identify/fix conflicts
• makes source readily available less duplicated
  effort

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Additional benefits

• Accountability
• who wrote the code?
• do we have the rights to it?
• Support software engineering
• hooks for peer reviews
• Software branches
• different versions of software need to be
  maintained, ensure bug fixes shared
• Record Keeping
• Commit logs may tie to issue tracking system or
  be used to enforce guidelines

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More Benefits

• Support Distribution of Work
• Telecommuting, outsourcing, open-source projects
• Use in conjunction with good communication
  habits via email etc.
• Rapid Development (XP/Agile)
• Supports frequent refactoring
• Helps automate frequent system builds

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Version Control Elements

• Repository and Working Directory
• Central repository. May be directory, database,
  distributed system. Developers do not work
  directly on files in repository.
• Working directory. Accessible from development
  machine. Local modifications made here.
  Complete changes committed back to repository.

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Version Control Elements

• Revisions
• Changes are stored in a revision. May be global
  or file-level.
• File-level each change of each source file is
  tracked. Tends to get unwieldy.
• Tags snapshot of repository at specific point.
• Differences between two revisions called a
  changeset.

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Version Control Elements

• Logs
• Need to know logical reasons for changes, not
  just what changes were made.
• Info stored just in source code comments becomes
  too hard to find.

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Version Control Elements

• Tags
• Can be placed at milestones
• Branching
• Parallel paths
• Branches can be worked on independently

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Version Control Elements

• Locking vs Merging
• Sometimes two developers need to modify one
  source at same time
• Most modern VCSs support merging
• File locking
• developer locks, no one else can change, commit
  and unlock when done
• enforces organized division of work, better if
  files cant easily be merged
• may block development, real problem if forget to
  unlock!

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Version Control Elements

• Merging
• Developers modify their own working copies
• When commit, VCS checks for collisions
• Will merge if possible
• Will require committer to make changes by hand if
  cant resolve conflicts
• Big advantage in systems where developers are
  likely to be working on parts of same file
• Frequent collisions can be a problem, if
  communication between developers is poor
• Either way
• Best practice is to update working copy with
  changes from repository, test your changes before
  you try to commit!