Jam is an open-source version control system for game development. We're building an open-source alternative to Perforce using Go and Content Defined Chunking (CDC) techniques. Join the Discord for questions or email me at zach@jamhub.dev.
Jam aims to solve the problems game developers have with currently available version control systems. Perforce, which is widely used in the gamedev industry, is closed-source, expensive and complicated. Open-source solutions like Git/GitLFS and SVN do not scale for large projects with large files. They are also missing features, like file locking, which are necessary for working with binary files that cannot be merged. By using modern Content-Defined-Chunking and hashing approaches we can also get performance improvements over current systems.
Jam is based off the rsync algorithm and FastCDC papers. If you haven't read these, I would highly recommend them! They're pretty approachable for anyone with a computer science background.
Content Defined Chunking is a method to split a file into predictable chunks while being able to recognize those chunks when shifted or modified. Google's cdc-file-transfer repository has some helpful information about the details of the algorithm for syncing two similar directories and a comparison to rsync. The main advantage of a CDC approach over rsync's fixed chunk size is the removal of the rolling hash lookup on every byte in the "no match" case. CDC bases the block boundaries on the content of the file, so insertions and deletions do not affect the boundaries of other blocks.
The main idea behind Jam is that blocks sent during the CDC syncing process can be used to track changes to a file. When changes are made locally, the blocks that are changed or reused can be logged by a server. Essentially, this creates a delta each time a push is made and we can use the delta to regenerate the file.
The storage of deltas and their usage to regenerate a file is similar to the Mercurial concept of a Revlog. However, there are several advantages of using chunks over a delta approach.
- Chunks can be regenerated and streamed independently
- Data pointers can directly reuse chunks from previous versions of a file
These two advantages are particularly useful when storing large files. Unlike Git's approach of storing the entire history of a file locally, which can get large over time, Jam stores only the blocks that have changed over time on the server so local storage never increases in size. Also, we do not have to cache the entire file to make the regeneration length small, since pointers can jump directly to the data. This is also an improvement over GitLFS which stores an entirely new snapshot of the file on every change.
This section is still in progress. Expect terminology to change during development.
- Mainline - The production history of the project. Made up of a series of "commits" that represent good versions of the project.
- Workspace - A workspace for developers to make changes in. Developers will make "changes" in their workspace and merge into the "mainline" when approved/ready. "Changes" will be tracked while in the workspace, but will be squashed into a single "commit" when merged into the mainline. Eventually, changes will be able to be synced live between local developer machine and their workspace.
- Change - A modification of a workspace while developers are working on their
project, made by doing a
jam push. - Commit - A modification of the production version of the project, made by merging in a "workspace".
- Merge - Occurs when a workspace is squashed and committed to the "mainline".
The goal is to be able to handle over 100M files and over 1TB-sized files in a single repository. We're not there yet in the current implementation (~1M files with 16GB-sized files) but should be there in the next couple months.
Jam is being written from scratch in Golang and uses mattn/go-sqlite3 to store projects and change information. gRPC and Protocol buffers are used for service definitions and data serialization.
Jam is currently in development. You can currently push, pull, workon workspaces, and merge workspaces. Over the next few months we'll be adding features to make this usable for regular development. The following features are planned:
- Multi-person project collaboration
- File locking
- File ownership and permissions
- Live file and change syncing
- Open API access
- NFS protocol implementation
If there are any additional features you would like to see, please make a discussion or email me at zach@jamhub.dev.
Note that this is for setting up development or compiling JamHub yourself. If you want binaries and installation instructions go to jamhub.dev/login. Documentation for self-hosting is going to be pretty sparse right now, but reach out on Discord if you need any help. The general steps are below and you should be able to solve most issues by resolving any errors/dependencies that occur.
- Install Go, Protoc, Make
- Setup env with Auth0 variables
- Run desired
maketarget
Email Zach Geier at zach@jamhub.dev or join the Discord