Transcript Configuration Management Seminar in Software Design - 2005/6 Aviva Dayan Arik Gendelman

Configuration Management
Seminar in Software Design - 2005/6
Aviva Dayan
Arik Gendelman
Pablo Galiana
What is Configuration Management?

The control of changes made throughout
the system lifecycle.
Allows changes to be evaluated before they
are approved.
 Considers interrelationships among system
components.

Configuration Management
Software Configuration Management

A software engineering discipline



Comprised of tools and techniques
used to manage change to software assets.
A set of activities to control change by:


identifying the products & establishing relationships
defining mechanisms for management, control,
auditing and reporting on changes made.
In short: “A methodology to control and manage
a software development project.”
Configuration Management
Why do we need SCM?

To manage:
Many people working on the same code.
 Projects delivered in several releases
(builds).
 Rapid evolution of software and hardware.
 Project surveillance:


i.e. project’s status, bugs, features, etc.
Concurrent support and development.
 Stress time requirements of projects.

Configuration Management
Goals of SCM

Configuration Control


Status Accounting

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Recording and reporting components’ status.
Review

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Controlling product release and its updates.
Ensuring completeness and consistency of all
parts.
Build Management

Managing the build process and its tools.
Configuration Management
Goals of SCM – cont.

Process Management


Environment Management


Ensuring adherence to the development
process.
Managing the components that host our
system.
Teamwork

Facilitate team interactions
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SCM – How it is accomplished?
All these goals are accomplished through
Version control
Management of multiple revisions of the
same unit of information.
Configuration Management
Version control

Commonly used in engineering and software
development.

Changes identified by incrementing an
associated number or letter code - “revision
number”, or “revision level”.

Revision numbers (levels) are associated
historically with the person making the change.
Configuration Management
Vocabulary

Repository


Check-Out
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
A server where the files are stored.
copies a working copy from the repository
(the opposite of an import).
Change


A specific modification to a document under version control.
The granularity of the modification considered a change varies
between version control systems.
Configuration Management
Vocabulary – cont.

Change List

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
Commit or Check-in

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The set of changes made in a single commit.
A sequential view of the source code.
Copy the changes on the local files to the directory.
(the VC software takes care of changes since the last
synchronization).
Update


copies the changes that were made to the repository into your
working directory.
(opposite of a commit).
Configuration Management
Vocabulary – cont.

Merge / Integration

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Revision or version

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one version in a chain of changes.
Conflict

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brings together (merges) concurrent changes into a unified
revision.
Occurs when two changes are made by different parties
to the same document or place within a document.
Resolve

The act of user intervention to address a conflict
between different changes to the same document.
Configuration Management
Example
CM Clients
Trunk
CM Server
Version A Branch
Machine A
Version A.1
Branch
Check Out
Check In
C
A
Machine B
B
Version B Branch
Check Out
D
Merge
E
Check In
Configuration Management
History

CM systems save the files’ history.

Old versions can be viewed, compared,
and downloaded.

New versions can be (irreversibly)
replaced with old versions and ‘wiped off
the map’.
Configuration Management
Central repositories

Files are saved in a central file server.

Developers can view the files in the
repository, through the use of filters.
Configuration Management
Labels

Several files can be labeled together.

Allows :
Access to the label as a whole set of files.
 Changes to the labeled files as a unit.

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Useful for marking product releases.
Configuration Management
Check-in

Copies a file into the database.
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The version you see is (usually) the
latest version that was checked in.

The old version is kept and can be
accessed later.
Configuration Management
Check out

Copies the database file to your personal
folder, and raises a flag on the database
copy.

Need to check out before checking in.
Configuration Management
Undo check out (uncheck-out)

The “undo checkout” command does just
that – the file returns to the status it had
before it was checked out.

This can be done even if changes have
been made to the local copy – of course,
these do not go into the database!
Configuration Management
Versioning Models
Lock-Modify-Unlock Solution:

Only one person can change a file at a time.

Example: VSS.
Copy-Modify-Merge Solution:
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Users modify private copies only - in parallel
 Private copies are merged together into a new,
final version.

Example: CVS, Subversion.
Configuration Management
Problems With Locking

Administrative problems:

A user can lock a file and forget about it.

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Time is wasted while others wait to edit the file.
Unnecessary serialization:

Different parts of a file don’t necessarily
overlap.

E.g.: Alice works on the beginning of a file, Bob
wants to edit the end of the same file.
Configuration Management
Problems With Locking – cont.

False sense of security:
Let’s say Alice locks and edits file A, while
Bob simultaneously locks and edits file B.
 Let’s say A and B depend on one another,
and the changes made to each are
semantically incompatible.
 Suddenly, A and B don't work together
anymore.

Configuration Management
The Copy-Modify-Merge Solution
Aviva and Arik both
check out file A.
Repository
Here, checkout has
no locking effect –
it’s just a local copy.
A
Read
Read
A
A
Configuration Management
The Copy-Modify-Merge Solution
Both edit their local files.
Repository
A
Aviva
Arik
Configuration Management
The Copy-Modify-Merge Solution
Aviva checks in her
file to the repository
first.
Repository
Aviva
Write
Aviva
Arik
Configuration Management
The Copy-Modify-Merge Solution
Now, Arik tries to
check-in his file.
Repository
He gets an “up-todate check error”
Aviva
Write
Aviva
Arik
Configuration Management
The Copy-Modify-Merge Solution
Arik updates his local copy
to contain the changes
made by Aviva. Changes
are added to the local file.
Repository
Aviva
During this merge, conflicts
may occur.
Read
A’
(=Aviva+Arik)
Configuration Management
Aviva
The Copy-Modify-Merge Solution
A new merged file
is created on Arik’s
machine.
Repository
Aviva
Aviva
B
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The Copy-Modify-Merge Solution
Arik commits his file
to the repository.
Repository
B
Write
B
Aviva
Configuration Management
The Copy-Modify-Merge Solution
Aviva updates her file from
the repository.
Repository
B
Read
B
B
Configuration Management
Check-out etiquette

If two people have a file checked out, they
have to merge their changes before check-in
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Merging files can be messy!
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This requires coordination and responsibility
on the part of developers, not to make
unnecessary check-outs, and not to hold
check-outs for too long.
Configuration Management
File Comparison
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Users can graphically compare two
versions of files, in or out of the
database.
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Tools: BeyondCompare, Windiff,
AraxisMerge…
This helps with manual merges
 Also helps people decide which version
to access
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Configuration Management
SourceSafe
Central repository of read-only files.
 Everybody sees the same version.
 Only one user can check in at once.

No branching.
 Limited merge capabilities.

Synchronized with Visual Studio
Configuration Management
Advantages of SourceSafe

Synchronized with Visual Studio.

Relatively inexpensive.
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Relatively simple to administrate.
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Disadvantages of SourceSafe

Does not support branching
Requires verbal coordination.
 Poses a problem for large projects.
 Complicates development of features

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Not compatible with other OS’s.
Configuration Management
Get Latest Version (?)

Getting the latest version copies (rather than
links) the file from the database to your
personal directory - And so:
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Getting latest version overwrites files in personal
folders.
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Rename local files beforehand if you want to keep them.
Database updates do not update local copies.
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Changes to database necessitate manual merges.
Configuration Management
Preserving Database Integrity
(or: watch SourceSafe limp…)
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Before a SourceSafe check-in:
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Verify thoroughly that the modified file works with other files
Otherwise there could be big trouble…
Other systems allow for new branches
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Files can be updated there.
Branch is merged with main trunk only after integrity checks.
Advantage: source control throughout the checking process!
Configuration Management
Demo- SourceSafe
Demo – SourceSafe
Configuration Management
Concurrent Versions System
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CVS has UNIX origins.
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Available also for Linux and Windows.
Stores only the differences between
versions.
Configuration Management
Clients

Command line.
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GUI (i.e. WinCVS, tkCVS, etc)
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NOTE: Most GUI/Plugins are wrappers
around the basic CVS command line client.
Configuration Management
Revisions

Each version of a file has a unique
Revision number. Revision numbers look
like ‘1.1’, ‘1.2’, ‘1.3.2.2’ or even
‘1.3.2.2.4.5’.
Main.c
1.1
1.2
1.3
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1.4
Revision Numbering
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By default:
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revision 1.1 is the first revision of a file.
Successive revisions incremement the
rightmost number.
Configuration Management
Tags

Tags are used to give a symbolic name
to a certain collection of file revisions.
Main.c
1.1
1.2
1.3
TAG_XXX
Main.h
Lala.c
1.1
1.1
1.2
1.2
1.3
Configuration Management
1.4
Branching
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Like ClearCase, CVS allows branches:
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Allows changes to be isolated into a
separate development line.
Branches are good for:
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Fixing bugs in historical releases.
Developing features without disrupting primary
development.
Configuration Management
Trunks and Branches

The main branch is called the “main
trunk”.

A branch can be merged back to the
main trunk, or left as a branch.
Configuration Management
Branches and Revisions
Branch 1.2.2.2.2 ->
Branch 1.2.2. ->
Main.h
1.1
Branch 1.2.4. ->
1.2.2.1
1.2
1.2.2.2.2.1
1.2.2.2.2.2
1.2.2.2
1.3
1.2.4.1
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1.4
1.2.4.2
Main Trunk
1.2.4.3
ClearCase - Overview
Rational ClearCase is a software tool for revision
control of source code and other software
development assets.
Basic concepts:
Items under ClearCase are generally referred to
as “elements”.
For example:
design models, source files, project files, DLLs, etc.
Configuration Management
VOB
All elements stored in VOBs – Version Object Bases.
Depending on the size and complexity of your SW
development environment – ClearCase elements
may be distributed across more than one VOB.
For example:
 elements used by the Documentation group can be stored
in one VOB, while elements contributing to software builds
can be stored in a different VOB.
Configuration Management
VOB – Illustration
This diagram
illustrates a VOB
that contains the
file elements :
prog.c,
util.h,
msg.cat,
and lib.c
Configuration Management
View
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To access an element under ClearCase,
you set up and work in a view,
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A view shows a directory tree of specific
versions of the element.
Configuration Management
Two kinds of views:
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Snapshot views
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copy files from VOBs to your computer.
Dynamic views,
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use the multiversion file system (MVFS) of
ClearCase to provide immediate,
transparent access to the data in VOBs.
Configuration Management
Configuration Specifications
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A set of rules called a configuration
specification determines which files are
in a view.

These rules are written in a special and
powerful script language.
Configuration Management
Version Trees

Each time an element is revised and
checked in, ClearCase creates a new
version of the element in the VOB.

ClearCase organizes the different
versions of an element in a VOB into a
version tree.
Configuration Management
Version Trees and Branches - Illustration
This
diagram
illustrates a
version tree
and several
branches:
Configuration Management
Advantages of ClearCase

Can handle projects that:
a) Consists from a lot of developers.
b) Go on for a very long time.
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Developed and marketed by IBM,
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i.e. very smooth and natural integration with a
lot of other IDE/CM/test/profiling… Tools.
Versatile – lots of possibilities and capabilities.
Configuration Management
Advantages – cont.
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Supported by multiple OS
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Windows, Unix (Solaris, AIX, …), Linux.
Can be accessed from client on one OS to a server
on another OS.
Enables real parallel development - work on
multiple versions of the same source file
concurrently.
Configuration Management
Disadvantages

High price.

Too versatile

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one can never learn all capabilities.
Complex support

must have very good - full time - administrator.
Configuration Management
ClearCase View Snapshots
Windows
Unix
Configuration Management
ClearCase Integrated in Visual Studio IDE.
Configuration Management
Checkout Operation Snapshot
Windows
Unix
Configuration Management
ClearCase Merge Utility
Windows
Unix
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Version Tree Snapshot
Windows
Unix
Configuration Management
General Info – Unix version
General
information
about a file
in the
repository –
in the Unix
GUI.
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Configuration Management
Configuration Management
THE END
Configuration Management