CSC/ECE 517 Fall 2013/ch1 1w01 aj

Version Control Tools

Version control tools are the tools which manage the changes to documents, computer programs, large web sites, and other collections of information. It is a repository of code along with the history of the changes. All the change made to the source is tracked, along with the other details like who made the changes, why the changes were made and other comments. This concept is very important for large projects requiring collaborated development. Whether it is the history of this wiki page or large software development project like Facebook, the ability to track the changes, and to reverse changes when necessary can make all huge difference between a well-managed and controlled process and an uncontrolled ‘first come, first served’ system. It can be used to track the development lifecycle of a project in detail.

Categories of version control tools

Distributed Model

Peer-to-peer approach is followed in distributed revision control system in which each person’s copy of codebase is the current version of his code. In this way, each developer has the copy of full code rather than a part of code on which that developer is working. This system then synchronizes the copies of each developer by exchanging patches which contain the sets of changes. In this way each developer gets the latest copy of the code portion that others are working on. This method, most of the times, does not use the central repository. Major advantages of this system are:

• As the full code is available on the hard disk, most of the actions are very fast as the interaction with the remote server is not required.

• Committing new change sets can be done locally without anyone else seeing them. Once you have a group of change sets ready, you can push all of them at once.

• Except pushing and pulling, most of the actions can be performed without an internet connection.

Despite the above advantages, Distributed Version Control Tools pose some problems. As the copy of whole code is maintained at the local machine, it requires a huge amount of space in case the files cannot be compressed (binary files). Moreover, in case the project has a huge history of changes, it might require large amount of time to download the entire patches.

Git

Git is a free and open source distributed version control system. Its highest priority is to provide the high speed to its users. It was initially designed and developed for Linux kernel in 2005. was originally designed as a low-level version control system engine on top of which others could write front ends. However, the core Git project has since become a complete version control system that is usable directly. As of today, Git is estimated to have captured 30% of the market. Every Git working directory is a full-fledged repository with complete history and full version tracking capabilities, not dependent on network access or a central server.

Some of the major characteristics of Git:

===== Good support for expansion ===== Git is extremely fast and scalable. Referring to a local copy of code instead of the copy on remote server is very fast. As the project size increases, the affect of size on performance is very less.

===== Distributed development ===== Each developer is provided with the local copy of the entire development history. Changes are copied from one of the repository to another. These changes are transferred and can integrate the same way the local branches of the repository.

===== Backward compatibility ===== Repositories can be published by HTTP, FTP, rsync, or a Git protocol over either a plain socket, ssh or HTTP. Git also has a CVS server emulation, which enables the use of existing CVS clients and IDE plugins to access Git repositories.

===== Non-linear development ===== Git provides quick branching and merging. A branch in git is only a reference to a single commit. It supports non-linear development through various tools.

===== Support for incomplete merge ===== In case of an incomplete merge, Git provides multiple algorithms for letting the user know of this situation and also provides support for manual editing.

===== Cryptographic authentication of history ===== Git stores the history so that the id of a particular version depends upon the history of changes resulting into that commit. Once it is published, it is not possible to change the old versions without it being noticed.

Some of the major companies using Git in their projects include Google, Facebook, Microsoft, Twitter and Eclipse.