2.1 Introduction to version control systems (VCS)

Version control systems are the backbone of modern software development. They track changes, enable collaboration, and provide a safety net for your code. Without them, managing complex projects would be a nightmare.

Git and SVN are two popular VCS options. Git's distributed model offers flexibility and speed, while SVN's centralized approach keeps things simple. Both have their strengths, so choose based on your team's needs and workflow preferences.

Version Control Systems in Software Development

Purpose and Benefits

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• Track and manage changes to files over time, enabling collaboration, versioning, and backup of codebases
• Allow multiple developers to work on the same codebase simultaneously without overwriting each other's changes by using branching and merging techniques
• Maintain a complete history of all changes made to the codebase, including who made the changes, when they were made, and what specifically was changed, providing accountability and the ability to revert to previous versions if needed
• Facilitate code reviews, as changes can be easily viewed, discussed, and approved before being merged into the main codebase
• Enable efficient backup and recovery of codebases, as the entire history is stored and can be easily restored in case of data loss or corruption (server failure, accidental deletion)
• Support parallel development, allowing different features or bug fixes to be developed independently on separate branches and merged back into the main codebase when ready

Collaboration and Workflow

• Enable multiple developers to collaborate on the same codebase by providing mechanisms for sharing, merging, and resolving conflicts in changes
• Provide a structured workflow for managing changes, typically involving creating a branch, making changes, staging and committing those changes, and then merging the branch back into the main codebase
• Allow for code reviews and discussions around changes before they are merged, improving code quality and knowledge sharing among team members
• Facilitate continuous integration and deployment (CI/CD) practices by providing a central repository and versioning system that can be integrated with build and deployment tools
• Support distributed teams and remote work by enabling developers to work offline and synchronize changes when connected to the network

Centralized vs Distributed Version Control

Centralized Version Control Systems (CVCS)

• Use a single central server to store the entire version history of the codebase, and clients must connect to this server to check out or commit changes
• Rely on a central server as a single point of failure, and if it goes down, collaboration and version control are disrupted
• Require network connectivity to perform most operations, as changes must be synchronized with the central server
• Provide a simpler and more straightforward model for collaboration, as there is a single source of truth for the codebase
• Examples of CVCS include Apache Subversion (SVN) and CVS

Distributed Version Control Systems (DVCS)

• Allow each client to have a full copy of the repository, including the entire version history, enabling offline work and reducing reliance on a central server
• Enable multiple remote repositories to be synchronized, allowing for more flexible collaboration models and reducing the risk of data loss
• Perform faster operations, as most actions (committing, branching, merging) can be performed locally without the need for network communication with a central server
• Provide more resilience and fault tolerance, as there is no single point of failure and repositories can be easily replicated and synchronized
• Examples of DVCS include Git, Mercurial, and Bazaar

Git and SVN Features

Git Features

• Distributed version control system that emphasizes speed, data integrity, and support for non-linear workflows through its branching and merging capabilities
• Uses a snapshot-based model, where each commit represents a complete snapshot of the codebase at a particular point in time, enabling efficient storage and retrieval of versions
• Supports lightweight branching and merging, allowing developers to easily create, switch between, and merge branches for parallel development and experimentation
• Provides a staging area (index) where changes can be selectively added before committing, enabling fine-grained control over what is included in each commit
• Offers powerful tools for resolving conflicts and maintaining a clean history, such as rebasing and cherry-picking
• Integrates well with popular collaboration platforms like GitHub, GitLab, and Bitbucket

SVN Features

• Centralized version control system that focuses on simplicity and ease of use
• Uses a central repository model, where all version history is stored on a single server, and clients check out working copies of the codebase
• Supports atomic commits, ensuring that a commit either succeeds completely or fails without changing the repository state
• Provides a simple branching and merging model, using a directory-based approach where branches are created as separate directories within the repository
• Offers good performance for handling large binary files and has a smaller repository size compared to Git
• Integrates with various IDEs and development tools through plugins and extensions

Version Control Workflow and Terminology

Basic Workflow

• Check out a working copy of the codebase from the repository
• Make changes to the files in the working copy
• Stage the modified files, selecting which changes should be included in the next commit
• Commit the staged changes, creating a new version in the project's history
• Push the local commits to a remote repository, making them available to other collaborators
• Pull changes made by other collaborators from the remote repository and merge them into the local working copy

Key Terminology

• Repository: a data structure that stores the complete version history of a project, including all files, directories, and metadata
• Clone: the process of creating a local copy of a repository, including all its history and branches
• Working copy: a local copy of the codebase that a developer can modify and update independently
• Staging (adding): the process of preparing changes to be committed by selecting the modified files that should be included in the next commit
• Commit: the action of permanently recording changes to the repository, creating a new version in the project's history
• Push: the process of transferring local commits to a remote repository, making them available to other collaborators
• Pull: the process of fetching changes from a remote repository and merging them into the local working copy
• Branch: a separate line of development, allowing parallel work on different features or bug fixes without affecting the main codebase
• Merge: the process of integrating changes from one branch into another, typically used to combine the work of parallel branches