Transcript Source Code Revision Control Software

Source Code Revision Control
Software
CVS and Subversion (svn)
Would these tools be useful for Noah development efforts?
Why use revision control software?

Concurrent development for multiple users
working from a single source-code base
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History (logging; revert to older versions)
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Tagging (version identification)
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Branching (merging)
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Archive (just archive the repository)
Caveats
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Revision control software is not a replacement
for:
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Developer communication, cooperation
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Code development project management
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Good habits on the part of code developers
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Meaningful log entries (change logs)
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Code development habits
Typical use
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Checkout code from the central repository
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Do your work
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make your modifications
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possibly add source-code files
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do your testing
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etc.
Commit your changes to the central repository
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Include a mandatory log entry describing your
changes
More typical use
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Update your working code to include changes
that others have comitted
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Merge conflicting changes
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Export code for release
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Tag a specific snapshot of the code (i.e., a
named version for release)
More typical use
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View file history, change logs
Make branches for more independent
development
Merge branches back into main code base
CVS or Subversion?
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At the level for basic usage, they are very
similar
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The goal of the Subversion project was to make a
near-lookalike replacement for CVS users
Similarities
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Similar workflow, similar user commands
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(Though I found branching and tags seemed to
make a lot more sense in Subversion)
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Each has readable, useful users’ guides online
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Each has a wide user base
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Used by many high-profile projects
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Actively maintained
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Open source
Reasons to choose Subversion for
Noah development?
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SVN has a newer code base than CVS

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Advantage? Disadvantage?
SVN seems to have more active development
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Advantage? Disadvantage?
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SVN has better file renaming capabilities
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SVN handles symbolic links

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SVN used at NCAR for WRF development, at NCEP for NMM
development
SVN seems to have more sensible tags and branches
Reasons to choose CVS for Noah
development?
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Long history
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RAL has a central CVS repository
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There has been talk of having a central RAL
Subversion repository
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Would Noah development take advantage of RAL
central repository?
CVS or Subversion?
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More important question:
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Would software version control through some
central repository be useful for Noah LSM
development
Discussion points
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Would such tools be useful for Noah development efforts?
Are the Noah development efforts coordinated enough to make
use of a centralized, single, repository?
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Multiple institutions (firewall issues?)
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Divergent interests and development directions
Would Noah development be better suited by each group
maintaining independent code?
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Periodic merging efforts to produce a new “unified” release
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Then every group starts again with their own development from that
common release
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Each group responsible for its own code maintenance strategies
Online Documentation
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Subversion
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http://svnbook.red-bean.com
CVS
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http://cvsbook.red-bean.com
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http://ximbiot.com/cvs/manual
Differences (at the user level)
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Revision numbers
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CVS version numbers apply to files
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Subversion version numbers apply to the repository
Directory versioning
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CVS does not apply revision numbers to directories
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Subversion revision numbers apply to the repository, and so to any directories in
the repository
Branches and tags
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Subversion branches and tags are simply copies of the repository filesystem
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CVS branches and tags get complicated
Properties
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Subversion allows arbitrary metadata tags to be applied to files
Release 1.0
Release 2.0
Release 1.0
Release 2.0
Concerted merge effort