Versioning Systems. Tolu Oguntusin(too06u) 12th November, University of Nottingham

Transcription

1 Introduction to in Software Quality. (too06u) University of Nottingham 12th November, 2008

2 Outline Introduction to in Software Quality. 1 Introduction to What are? How do they work? How are files stored? 2 Client-server/Centralised Architecture: Distributed/Decentralised Architecture (DVCS) Client-Server Vs DVCS 3 Concurrent Versions System (CVS) Git 4 in Software Quality.

3 Introduction to in Software Quality. What are? Definition How do they work? How are files stored? Versioning systems/ Version control systems are software systems used by engineers, artists, software developers to manage and keep track of all work and all changes in files and allows several developers/editors (potentially widely separated in space and/or time) to collaborate their work

4 Introduction to in Software Quality. How do they work? Definition How do they work? How are files stored? Concurrent file access - There are two main model used to manage concurrent acces to files in VCS:- File locking - only one developer at a time has write access to the central "repository" copies of a file Version merging - Numerous developers are allowed to work on files simulteanously, and changes are merged Each developer checks out the most recent copy of a file from the repository before working on it. After changes are made, developers commit the files back to the repository If there are contradicting changes to the same file, the commit is rejected and the developer will need to manually merge the file.

5 Introduction to in Software Quality. How do they work? (2) Definition How do they work? How are files stored? Changes to documents are identified by associated version numbers which are incremented automatically by the versioning system The system also records the name of the developer/editor that turns in the new version of the document. The systems also provides an historical catalogue of the diffferent file versions making it possible to revert to an older versions of documents

6 Introduction to in Software Quality. Revision storage models Definition How do they work? How are files stored? Versioning systems use a compression format called delta compression. There are two revision storage models Snapshot model - complete files are stored for the entire repository for each revision. Changeset model - only the deltas are stored between revisions, creating a compact repository In the snapshot model, access to revision is very quick, however it requires a sacrifice of storage space. The changeset model requires less space, but performance is slower.

7 Client-Server Introduction to in Software Quality. Client-server/Centralised Architecture: Distributed/Decentralised Architecture (DVCS) Client-Server Vs DVCS The historical and most common architecture found today is the centralized repository Developers check-out or update source code from the central source repository (server) into a local sandbox Make changes Commit to their changes to the server Source : Version Control for Linux, 2006[1] Branches can also be created at the central repository but is better handled in the distributed architecture.

8 DVCS Introduction to in Software Quality. Client-server/Centralised Architecture: Distributed/Decentralised Architecture (DVCS) Client-Server Vs DVCS This architecture takes a peer-to-peer approach as opposed to the centralized system. Each user has a local repository which is a full-fledged repository with complete history and full revision tracking capabilities not dependent on network access or a central server. Synchronisation is conducted by exchanging patches (changeset) via peer to peer between users

9 DVCS Introduction to in Software Quality. Client-server/Centralised Architecture: Distributed/Decentralised Architecture (DVCS) Client-Server Vs DVCS Source : Version Control for Linux, 2006[1] This is the model for many open source systems today, including the Linux kernel.

10 Introduction to in Software Quality. Client-Server Vs DVCS Client-server/Centralised Architecture: Distributed/Decentralised Architecture (DVCS) Client-Server Vs DVCS Distributed Client-Server Versioning Systems Systems Not easy. Users have to manually Branching and track revisions Merge Capability between merged Simple branches Peer to Peer synchronisation Not supported Supported Offline commits Not supported Supported Data Backup Moderate Excellent Performance Slow Fast Complexity Need to dedicate Easy to setup and time to learning the use system

11 CVS Introduction to in Software Quality. Concurrent Versions System (CVS) Git CVS is historically the first of its kind and it was released by Dick Grune in It uses the centralised repository architecture Uses the changeset model for revision storage. CVS is relatively easy to install and learn. However CVS has its flaws. CVS is available as a standalone application (WinCVS, TortoiseCVS) and also as a plugin for a number of IDEs (NetBeans, Eclipse,Emacs). Others like Subversion (SVN) improve on the flaws of CVS

12 Git Introduction to in Software Quality. Concurrent Versions System (CVS) Git Git was initially developed by Linux kernel creator Linus Torvalds, and is fast growing in popularity as the new VCS. Git functions on a distributed version control architecture. It uses the snapshot model for revision storage Git places its pride on being a fast and efficient system. Git is not as user-friendly as CVS or SVN Branching and merging are fast and easy to do unlike CVS and SVN. A popular front-end for GIT is called GitHub. Other like Mecurial, re-knowned for it s performance, and Bazaar which is known for its flexibility and user friendliness Version control for human beings.

13 Introduction to in Software Quality. Concurrent Versions System (CVS) Git Comparison of Version Control Systems Repository model Access model Storage model Atomic commits Merge tracking File renames Merge file renames CVS SVN Git Hg Bazaar Client -Server Merge Changeset Client- Server Merge or Lock Changeset or Snapshot Distributed Distributed Distributed Merge Merge Merge Snapshot Changeset Snapshot No Yes Yes Yes Yes No Yes (New feature) Yes Yes Yes No Yes Yes Yes Yes No No Yes Yes Yes Cost Free Free Free Free Free Source : Version Control for Linux, 2006[1]

14 Appendix Importance to QAT & Summary Allows unlimited number of people working on the same code base, which reduces development time. Provides logs useful for tracking and accounting for ownership of changes Developers are able to attach comments and notes to each commit this in effect helps the assembly of comprehensive documentation for the software Overall it can be said that versioning systems are powerful development management tools that provide security, efficiency and most importantly an asynchronous platform for software development.

15 Appendix For Further Reading For Further Reading I B. Collins-Sussman, B. Fitzpatrick, C. Pilato. Version Control with Subversion. O Reilly Media,Inc., J. Vesperman. Essential CVS, 2nd edition. O Reilly Media,Inc., 2007.

16 Appendix For Further Reading References M. Tim Jones., 2006 Version control for Linux: An overview of architectures, models, and examples. IBM DeveloperWorks [Online] Available at [Accessed 13 November 2008] Wikipedia.org Comparison of revision control Software. Wikipedia [Online] Available at [Accessed 10 November 2008]