Distributed Concurrent Versions System
Encyclopedia
The Distributed Concurrent Versions System (DCVS) is a distributed revision control
system that enables software developers working on locally distributed sites to efficiently collaborate on a software project. DCVS is based on the well known version control system Concurrent Versions System
. The code is freely distributable under the GNU and BSD style licenses.
, a program developed by John D. Polstra. The combination of DCVS repository, extended CVSup server and DCVS server program will be called DCVS server in the following paragraphs.
All contents of all development lines can be checked out from any of the DCVS servers into a DCVS workspace owned by a developer. All operations that do not modify the repository, such as diff
, patch
, log
, annotate etc., work just like in CVS, but they always use the local repository and so are much faster in a distributed scenario.
In order to avoid collisions and data loss every DCVS server gets assigned a set of development lines (DCVS branches) for which it is
responsible. Modifications to a branch may only be checked in on the server which is responsible for the branch. The separation of
modifications by lines of development makes it possible to automatically transfer and distribute changes in the DCVS network.
A person wanting to commit changes for a development line that his local DCVS server is not responsible for can create a new
development line (branch) and commit the changes to it. The local server is automatically responsible for any newly created line of
development.
On the other hand, every developer can merge changes from development lines his local DCVS server is not responsible for into local
development lines. Thus all changes made at any working site may be applied to the original branch by developers on the responsible DCVS server performing a merge
operation.
The functionality of change sets enables developers to produce small sets of changes related to a feature or a defect, which can then be applied by others.
A specific numbering scheme ensures that development lines and deltas can be identified as belonging to a certain DCVS server. DCVS
assigns a unique range
of branch numbers to every pair (server/collection). All ranges for all servers and collections must be mutually exclusive. The definitions for servers, collections, and ranges are read from a single configuration file. By consulting the contents of this file, every DCVS server can decide if it is responsible for a certain branch or delta of a given file. If so, all modifying operations are allowed; if not, modifying operations are only possible on the appropriate remote server.
Also the actual names of configurations, the tags
, are uniquely assigned to exactly one DCVS server by means of a server-specific suffix extending all tags (i. e. _at_dcvs_mydomain_org). Thus no conflicts in the tag name space may arise.
Distributed revision control
A distributed revision control system , distributed version control or decentralized version control keeps track of software revisions and allows many developers to work on a given project without necessarily being connected to a common network.-Distributed vs...
system that enables software developers working on locally distributed sites to efficiently collaborate on a software project. DCVS is based on the well known version control system Concurrent Versions System
Concurrent Versions System
The Concurrent Versions System , also known as the Concurrent Versioning System, is a client-server free software revision control system in the field of software development. Version control system software keeps track of all work and all changes in a set of files, and allows several developers ...
. The code is freely distributable under the GNU and BSD style licenses.
Motivation
CVS is based on a pure centralistic organizational model and offers very little offline support. Almost all version control operations require direct access to the repository. Therefore worldwide distributed software development efforts face heavy performance problems when using CVS. DCVS tackles this issue by distributing the central CVS repository on many sites.Features
DCVS provides all CVS functionality. But unlike CVS a DCVS system may comprise an arbitrary number of geographically distributed repositories whose contents are kept equal in the background by an extended version of CVSupCVSup
CVSup is a computer program written for Unix/Linux based systems that synchronizes files and directories from one location to another while minimizing data transfer using file-type specific delta encoding when appropriate...
, a program developed by John D. Polstra. The combination of DCVS repository, extended CVSup server and DCVS server program will be called DCVS server in the following paragraphs.
All contents of all development lines can be checked out from any of the DCVS servers into a DCVS workspace owned by a developer. All operations that do not modify the repository, such as diff
Diff
In computing, diff is a file comparison utility that outputs the differences between two files. It is typically used to show the changes between one version of a file and a former version of the same file. Diff displays the changes made per line for text files. Modern implementations also...
, patch
Patch (Unix)
patch is a Unix program that updates text files according to instructions contained in a separate file, called a patch file. The patch file is a text file that consists of a list of differences and is produced by running the related diff program with the original and updated file as arguments...
, log
Log
Log, LOG, or LoG may refer to:*Wooden log, also known as timber, wood from trees used for construction, fuel, or wood pulp for paper production...
, annotate etc., work just like in CVS, but they always use the local repository and so are much faster in a distributed scenario.
In order to avoid collisions and data loss every DCVS server gets assigned a set of development lines (DCVS branches) for which it is
responsible. Modifications to a branch may only be checked in on the server which is responsible for the branch. The separation of
modifications by lines of development makes it possible to automatically transfer and distribute changes in the DCVS network.
A person wanting to commit changes for a development line that his local DCVS server is not responsible for can create a new
development line (branch) and commit the changes to it. The local server is automatically responsible for any newly created line of
development.
On the other hand, every developer can merge changes from development lines his local DCVS server is not responsible for into local
development lines. Thus all changes made at any working site may be applied to the original branch by developers on the responsible DCVS server performing a merge
Merge (revision control)
Merging in revision control, is a fundamental operation that reconciles multiple changes made to a revision-controlled collection of files. Most often, it is necessary when a file is modified by two people on two different computers at the same time...
operation.
The functionality of change sets enables developers to produce small sets of changes related to a feature or a defect, which can then be applied by others.
A specific numbering scheme ensures that development lines and deltas can be identified as belonging to a certain DCVS server. DCVS
assigns a unique range
Range
-In mathematics:* Range , the set of all output values produced by a function* Interval , also called a range, a set of real numbers that includes all numbers between any two numbers in the set...
of branch numbers to every pair (server/collection). All ranges for all servers and collections must be mutually exclusive. The definitions for servers, collections, and ranges are read from a single configuration file. By consulting the contents of this file, every DCVS server can decide if it is responsible for a certain branch or delta of a given file. If so, all modifying operations are allowed; if not, modifying operations are only possible on the appropriate remote server.
Also the actual names of configurations, the tags
Tag (metadata)
In online computer systems terminology, a tag is a non-hierarchical keyword or term assigned to a piece of information . This kind of metadata helps describe an item and allows it to be found again by browsing or searching...
, are uniquely assigned to exactly one DCVS server by means of a server-specific suffix extending all tags (i. e. _at_dcvs_mydomain_org). Thus no conflicts in the tag name space may arise.