Skip to main content
Enterprise Agile Planning icon with arrows

This post is from the CollabNet VersionOne blog and has not been updated since the original publish date.

Last Updated Mar 30, 2007 — Enterprise Agile Planning expert

How Subversion conserves disk space

Enterprise Agile Planning

I wanted to share something from our March openCollabNet Technical Newsletter. If you do not get our newsletter yet, sign up for openCollabNet. It only takes a minute.

To keep the size of the repository as small as possible, Subversion uses deltification, also called "deltified storage". Deltification is the encoding of a chunk of data as a collection of differences against some other data. If two files are very similar, deltification results in storage savings because only the changes are stored, not the entire file.

This works differently depending on what filesystem back-end you use. In BDB (Berkeley Database) fulltexts are found at the tips of each distinct line of a file’s history. When a change occurs, the new version is stored as fulltext, then the previous version is rewritten as a delta against that new version. FSFS stores deltas in the opposite direction so that old versions never need to be rewritten.  When a file is changed, the new version is stored as a delta against an older version.

Most source code files change frequently and Subversion’s performance would degrade if it had to use every individual delta to re-create a file that has changed many times. Subversion uses "skip-deltas" to improve performance. Skip-deltas are deltas that are calculated not against the immediate next or previous version, but against a version that’s closer in the chain of deltas to a fulltext representation of the file. This way the version of a file can be re-created using less deltas than when a delta for each individual change would be needed.

For repositories created with Subversion 1.4 or later, space savings increase further because the delta chunks are stored using a compression algorithm.

More from the Blog

View more
Digital.ai Government Cloud
Apr 12, 2022

Digital.ai Government Cloud receives FedRAMP Authorization through sponsorship from the United States Department of Veterans Affairs

Enterprise Agile Planning
Flagship Digital.ai Agility solutions can effectively scale agile deve ...
Read More
Nov 22, 2021

What are the qualities of highly effective agile teams?

Enterprise Agile Planning
A team is the core unit of productivity in an agile organization. Wher ...
Read More
Nov 15, 2021

How an open-first attitude revolutionized government tech development

Enterprise Agile Planning
Public perception of government is often that it is slow-moving, reluc ...
Read More
cross functional
Nov 08, 2021

6 best practices for building resilient cross-functional teams

Enterprise Agile Planning
Agile frameworks prize the quality of resilience within every facet of ...
Read More
Contact Us