Nuescheler explained how a content repository can fit into a typical web application. A JCR offers similar transactionality, scalability, and query support for structured data as a RDBMS but adds support for unstructured content, build in versioning, and "node-based" access control.
The Apache Jackrabbit project is an open source implementation of the JSR 170. InfoQ asked Nuescheler about the differences between Jackrabbit and CRX:
CRX can be considered as the commercialized Jackrabbit with a number of optimizations, added features, and easy to use packaging. CRX also features commercial grade support, release management and product management. Since featurewise Jackrabbit is the only complete opensource JCR implementation one can also expect the complete JCR featureset in CRX.
To increase performance for demanding environments, CRX 1.2 leverages the Apache Derby Persistance Manager. When asked about why CRX is using Apache Derby instead of Berkely DB Nuescheler responded:
a number of projects including Jackrabbit and also JDK 1.6 are using Derby. As a result it is a well tested and futureproof default persistance layer...
The new release of CRX also adds Active / Passive Clustering. This features a central, high-availability database server for permanent storage, and two CRX servers for non-permanent storage. Nuescheler commented:
active/passive clustering allows to hot failover from the active cluster node to the passive cluster node that is running on the same persistence layer for example a shared RDBMS. This allows us to avoid a single point of failure on the repository layer.This new clustering implementation improves cache management and performance in environments with large volumes of data and transaction loads.
We are working at the forefront of making the java content repository market viable for commercial grade applications. This is similar to what oracle did to the db market in the early days of sql. We are responding to the CRX community's needs and optimizing for those cases. This means for example that we support smart batch reads and batch writes (bundles) that enhance scalability drastically.
