Content deleted Content added
m Reverted edits by 185.181.109.220 (talk) (AV) |
|||
| (46 intermediate revisions by 36 users not shown) | |||
Line 1:
{{Short description|Software engineering tool}}
[[File:Git session.svg|thumb|The process of initializing a git repository. Git is one of the most popularly used distributed version control software.]]
In [[software development]], '''distributed version control''' (also known as '''distributed revision control''') is a form of [[version control]] in which the complete [[codebase]], including its full history, is mirrored on every developer's computer.<ref name="git-scm">{{cite book | chapter =
In 2010, software development author [[Joel Spolsky]] described distributed version control systems as "possibly the biggest advance in software development technology in the [past] ten years".<ref name="Joel 2010">{{cite web
Line 12 ⟶ 13:
==Distributed vs. centralized==
Distributed version control systems (DVCS) use a [[peer-to-peer]] approach to [[version control]], as opposed to the [[client–server model|client–server]] approach of centralized systems. Distributed revision control synchronizes repositories by transferring [[Patch (Unix)|patches]] from peer to peer. There is no single central version of the codebase; instead, each user has a working copy and the full change history.
'''Advantages of DVCS (compared with centralized systems) include:'''
* Allows users to work productively when not connected to a network.
* Common operations (such as commits, viewing history, and reverting changes) are faster for DVCS, because there is no need to communicate with a central server.<ref name='OSullivan'>{{cite web
Line 24 ⟶ 25:
* Allows private work, so users can use their changes even for early drafts they do not want to publish.{{cn|date=August 2019|reason=This isn't unique to dvcs; any source code control system allows 'private work', though on some it requires changing (private) file permissions}}
* Working copies effectively function as remote backups, which avoids relying on one physical machine as a single point of failure.<ref name='OSullivan'/>
* Allows various development models to be used, such as using [[Branching (version control)#Development branch|development branches]] or a Commander/Lieutenant model.<ref>{{
* Permits centralized control of the "release version" of the project{{cn|date=August 2019|reason=Not specific to dvcs; centralized systems generally control release version}}
* On [[FOSS]] software projects it is much easier to create a [[Fork (software development)|project fork]] from a project that is stalled because of leadership conflicts or design disagreements.
'''Disadvantages of DVCS (compared with centralized systems) include:'''
* Initial checkout of a repository is slower as compared to checkout in a centralized version control system, because all branches and revision history are copied to the local machine by default.
* The lack of locking mechanisms that is part of most centralized VCS and still plays an important role when it comes to non-mergeable binary files such as graphic assets or too complex single file binary or XML packages (e.g. office documents, PowerBI files, SQL Server Data Tools BI packages, etc.).{{citation needed|date=January 2018}}
* Additional storage required for every user to have a complete copy of the complete codebase history.<ref>{{cite web|title=What is version control: centralized vs. DVCS|url=https://www.atlassian.com/blog/software-teams/version-control-centralized-dvcs|website=www.atlassian.com|date=14 February 2012 |access-date=7 January 2018}}</ref>
* Increased exposure of the code base since every participant has a locally vulnerable copy.{{cn|date=August 2019|reason=Also true of centralized codebases}}
Some originally centralized systems now offer some distributed features.
Similarly, some distributed systems now offer features that mitigate the issues of checkout times and storage costs, such as the [[Virtual File System for Git]] developed by Microsoft to work with very large codebases,<ref>{{cite web|author=Jonathan Allen|url=https://www.infoq.com/news/2017/02/GVFS/|title=How Microsoft Solved Git's Problem with Large Repositories|date=2017-02-08|access-date=2019-08-06}}</ref> which exposes a virtual file system that downloads files to local storage only as they are needed.
Line 41 ⟶ 42:
{{Expand section|date=June 2008}}
A distributed model is generally better suited for large projects with partly independent developers, such as the [[Linux kernel|Linux Kernel]]. It allows developers to work in independent branches and apply changes that can later be committed, audited and merged (or rejected)<ref>{{Cite web |title=Submitting patches: the essential guide to getting your code into the kernel — The Linux Kernel documentation |url=https://www.kernel.org/doc/html/v5.1/process/submitting-patches.html |access-date=2024-11-22 |website=www.kernel.org}}</ref> by others. This model allows for better flexibility and permits for the creation and adaptation of custom source code branches ([[Fork (software development)|forks]]) whose purpose might differ from the original project. In addition, it permits developers to locally clone an existing code repository and work on such from a local environment where changes are tracked and committed to the local repository<ref>{{Cite web |title=Git - Revision Selection |url=https://git-scm.com/book/en/v2/Git-Tools-Revision-Selection |access-date=2024-11-22 |website=git-scm.com}}</ref> allowing for better tracking of changes before being committed to the master branch of the repository. Such an approach enables developers to work in local and disconnected branches, making it more convenient for larger distributed teams.
===Central and branch repositories===
In a truly distributed project, such as [[Linux]], every contributor maintains their own version of the project, with different contributors hosting their own respective versions and pulling in changes from other users as needed, resulting in a general consensus emerging from multiple different nodes. This also makes the process of "forking" easy, as all that is required is one contributor stop accepting pull requests from other contributors and letting the codebases gradually grow apart.
This arrangement, however, can be difficult to maintain, resulting in many projects choosing to shift to a paradigm in which one contributor is the universal "upstream", a repository from whom changes are almost always pulled. Under this paradigm, development is somewhat recentralized, as every project now has a central repository that is informally considered as the official repository, managed by the project maintainers collectively. While distributed version control systems make it easy for new developers to "clone" a copy of any other contributor's repository, in a central model, new developers always clone the central repository to create identical local copies of the code base. Under this system, code changes in the central repository are periodically synchronized with the local repository, and once the development is done, the change should be integrated into the central repository as soon as possible.
Organizations utilizing this centralize pattern often choose to host the central repository on a third party service like [[GitHub]], which offers not only more reliable [[uptime]] than self-hosted repositories, but can also add centralized features like [[issue tracking system|issue trackers]] and [[continuous integration]].
===Pull requests===
Contributions to a source code repository that uses a distributed version control system are commonly made by means of a '''pull request''', also known as a '''merge request'''.<ref name="gitlab-merge-req">{{cite web|last=Sijbrandij|first=Sytse|title=GitLab Flow|date=29 September 2014|access-date=4 August 2018|website=GitLab|url=https://about.gitlab.com/2014/09/29/gitlab-flow/}}</ref> The contributor requests that the project maintainer ''pull''
The developer creates a pull request to notify maintainers of a new change; a comment thread is associated with each pull request. This allows for [[Code review|focused discussion of code changes]]. Submitted pull requests are visible to anyone with repository access. A pull request can be accepted or rejected by maintainers.<ref>{{cite web|title=Using pull requests|url=https://help.github.com/articles/using-pull-requests/|publisher=GitHub|access-date=27 March 2016}}</ref>
Once the pull request is reviewed and approved, it is merged into the repository. Depending on the established workflow, the code may need to be tested before being included into official release. Therefore, some projects contain a special branch for merging untested pull requests.<ref name="ossw" /><ref>{{cite web|title=Making a Pull Request|url=https://www.atlassian.com/git/tutorials/making-a-pull-request|publisher=Atlassian|access-date=27 March 2016}}</ref> Other projects run an automated test suite on every pull request, using a [[continuous integration]] tool
==History==
Line 63 ⟶ 66:
{{columns-list|colwidth=30em|
* [[Version control]]
* [[List of version
* [[Comparison of version
* [[:Category:Software using distributed version control]]
* [[Repository clone]]
* [[
* [[Mercurial]], a cross-platform system similar to Git
* [[Fossil (software)|Fossil]], a distributed version control system, bug tracking system and wiki software
* [[BitKeeper]]
* [[GNU Bazaar]]
* [[Darcs]]
* [[Concurrent Versions System]], a predecessor of distributed version control systems
* [[TortoiseHg]], a graphical interface for Mercurial
| |||