What's the Difference Between Apache Jackrabbit and Jackrabbit Oak?

Question

I'm sorry if this sounds stupid, but what's the difference between Jackrabbit and Oak? I'm looking into JCR170, specifically how to migrate content between two jackrabbit installations, and I've come across both JackRabbit and Oak.

The Apache Jackrabbit™ content repository is a fully conforming implementation of the Content Repository for Java Technology API (JCR, specified in JSR 170 and JSR 283).

A content repository is a hierarchical content store with support for structured and unstructured content, full text search, versioning, transactions, observation, and more.

Jackrabbit Oak is a complementary implementation of the JCR specification. It is an effort to implement a scalable and performant hierarchical content repository for use as the foundation of modern world-class web sites and other demanding content applications. See the Jackrabbit Oak website for more information.

Apache Jackrabbit is a project of the Apache Software Foundation

http://jackrabbit.apache.org/jcr/index.html

Their own home page says that Jackrabbit is a content repository implementing JCR and that Oak is a complementary implementation of JCR. Why is there two implementations of JCR by the same project?

Answer 1

As awd mentioned in the comment, Oak is just the latest version of Jackrabbit. It is not just an update, but rather a new implementation of the same JSR170. So the API does not change, but the underlying inner workings are a bit different. You can find a lot in the documentation as Julian mentions. Some of the major changes are:

• Session handling: each session gets a snapshot of the repository when it was created to prevent concurrent changes on the repo: http://jackrabbit.apache.org/oak/docs/architecture/transactional-model.html
• MicroKernels: with which you can define how the repository is stored. Currently as before with tar files called tarMK or the NoSQL DB MongoDB with the mongoMK.

Here is an overview of the changes: http://jackrabbit.apache.org/oak/docs/differences.html

And a short slideshow: https://www.slideshare.net/jukka/oak-the-architecture-of-apache-jackrabbit-3