Apache Subversion (often abbreviated SVN, after the command name svn) is a software versioning and a revision control system founded and sponsored in 2000 by CollabNet Inc. Developers use Subversion to maintain current and historical versions of files such as source code, web pages, and documentation. Its goal is to be a mostly-compatible successor to the widely used Concurrent Versions System (CVS).
The open source community has used Subversion widely: for example in projects such as Apache Software Foundation, Free Pascal, FreeBSD, GCC, Django, Ruby, Mono, SourceForge, ExtJS, Tigris.org, PHP, Python and MediaWiki. Google Code also provides Subversion hosting for their open source projects. BountySource systems use it exclusively. CodePlex offers access to Subversion as well as to other types of clients.
The corporate world has also started to adopt Subversion. A 2007 report by Forrester Research recognized Subversion as the sole leader in the Standalone Software Configuration Management (SCM) category and as a strong performer in the Software Configuration and Change Management (SCCM) category.
Subversion uses the Apache License, making it free software and open source.
Repository types
Subversion offers two types of repository storage —
FSFS and Berkeley DB.
FSFS
FSFS works faster on directories with a large number of files and takes less disk space, due to less logging.[5] Beginning with Subversion 1.2, FSFS is the default data store for new repositories.
Berkeley DB
Subversion has some limitations with Berkeley DB usage when a program that accesses the database crashes or terminates forcibly. No data loss or corruption occurs, but the repository is offline while Berkeley DB replays the journal and cleans up any outstanding locks. When using Berkeley DB repository, the only way to use it safely is on the dedicated server and by a single server process running as one user, according to Version Control with Subversion. Existing tools for Berkeley DB repository recovery aren't completely reliable, so system administrators need to make frequent repository backups.
Repository access
Main article: Comparison of Subversion clients
Access to Subversion repositories can take place by the following means:
Local filesystem or network filesystem, accessed by client directly. This mode uses the file:///path access scheme.
WebDAV/Delta-V (over http or https) using the mod_dav_svn module for Apache 2. This mode uses the http://host/path access scheme or https://host/path for secure connections using ssl.
Custom "svn" protocol (default port 3690), using plain text or over SSH. This mode uses either the svn://host/path access scheme for unencrypted transport or svn+ssh://host/path scheme for tunneling over ssh.
All three means can access both FSFS and Berkeley DB repositories.
Any 1.x version of a client can work with any 1.x server. Newer clients and servers have additional features and performance capabilities, but have fallback support for older clients/servers.
Filesystem
One can view the Subversion filesystem as "two-dimensional". Two coordinates are used to unambiguously address filesystem items:
Path (regular path of Unix-like OS filesystem) Revision
Each revision in a Subversion filesystem has its own root, which is used to access contents at that revision. Files are stored as links to the most recent change; thus a Subversion repository is quite compact. The system consumes storage space proportional to the number of changes made, not to the number of revisions.
The Subversion filesystem uses transactions to keep changes atomic. A transaction operates on a specified revision of the filesystem, not necessarily the latest. The transaction has its own root, on which changes are made. It is then either committed and becomes the latest revision, or is aborted. The transaction is actually a long-lived filesystem object; a client does not need to commit or abort a transaction itself, rather it can also begin a transaction, exit, and then can re-open the transaction and continue using it. Multiple clients can access the same transaction and work together on an atomic change, though no existing clients expose this capability.
( Source From Wiki )
