Configuration Management

1
Configuration Management

• Colin Potts
• CS 3300

2
Exercise Three Problems

• Get into groups of three
• Reading the cases
• Individually read one of the cases and answer the
  questions that follow it
• Describe the case and the general problem you
  think it illustrates to the others
• Summarizing the cases
• Youll be called on to summarize a case you
  didnt read

3
The three problems

• Eric Ws. short-cut
• Multiple copies
• Multiple copies always diverge

• D Js unfixed fixes
• Simultaneous update
• The latest save overwrites the earlier ones

• Bill Us final bug correction
• Shared data
• A localized error has pervasive effect

4
Configurations

• A configuration is
• a selection of software components that are built
  together to make a system.
• More generally, a group of interrelated documents
  that should be changed in a coordinated way

5
Versions

• System1 System2 are versions
• Maybe System2 is a revision of System1
• Or maybe it is a variation of System1 (for a
  different OS?)
• Systems their components may be versioned
• Versions may be physically separate or generated
  / linked conditionally from a common source

E
6
Physical nature of versions

• Separate files
• A1 and A2 are in different files
• Deltas (of revisions) and branches (of
  variations)
• A1 through An are in one file that contains the
  latest (or earliest or branch point) version and
  representation of the changes
• E.g. Unix SCCS and RCS
• Conditional compilation (of variations)
• A1 and A2 dont exist (as source). Instead A
  contains directives to compile into A1 or A2
  conditionally on environment
• E.g. ifdef in C

7
Stability

• Baseline is a configuration that is standard
• E.g. current release to customers. Current
  development version
• Baseline is frozen or gelled
• No changes ever made (e.g. copy of customer
  release becomes new devt. version)
• OR baseline changes only when programmers are
  confident that they have made changes correctly
• Programmers work on private copies of components
• Check out copy from baseline, make changes, check
  back in (or create new config.) Personal copy is
  invisible to others.

8
Illustration of check-out check-in
copy
Baseline
BDef
Personal
(check out)
AOK
correct
Personal
overwrite
Baseline
BOK
(check in)
AOK
9
Potential problems

• Simultaneous update
• Can two programmers check out B and make
  inconsistent changes?
• Not if checking out also locks B
• Can two programmers simultaneously make
  incompatible changes to A and B
• No
• Multiple copies
• What if programmer only checks in source code of
  modified version (so object code is old)
• Use build tool, like make to enforce dependencies