I have an instance of XWiki finally running on Cassandra. http://kk.l.to:8080/xwikiOnCassandra/ Cassandra is a "NoSQL" database, unlike a traditional SQL database it cannot do advanced queries but it can store data in a more flexible way eg: each row is like a hashtable where additional "columns" can be added at will. The most important feature of Cassandra is that multiple Cassandra nodes can be connected together into potentially very large "swarms" of nodes which reside in different racks or even data centers continents apart, yet all of them represent the same database. Cassandra was developed by Facebook and their swarm was said to be over 200 nodes strong. In it's application with XWiki, each node can have an XWiki engine sitting on top of it and users can be directed to the geographically closest node or to the node which is most likely to have a cache of the page which they are looking for. Where a traditional cluster is a group of XWiki engines sitting atop a single MySQL engine, this allows for a group of XWiki engines to sit atop a group of Cassandra engines in a potentially very scalable way. In a cloud setting, one would either buy access to a provided NoSQL store such as Google's BigTable or they would setup a number of XWiki/Cassandra stacks in a less managed cloud such as Rackspace's or Amazon's. How it works: XWiki objects in the traditional Hibernate based storage engine are persisted by breaking them up into properties which are then joined again when the object is loaded. A user object which has a name and an age will occupy a row in each of three tables, the xwikiobjects table, the xwikistrings table, and the xwikiintegers table. The object's metadata will be in the xwikiobjects table while the name will be in a row in the xwikistrings table and the age, a number, will go in the xwikiintegers table. The NoSQL/Datanucleus based storage engine does this differently, the same object only occupies space in the XWikiDocument table where it takes advantage of Cassandra's flexibility by simply adding a new column for each property. NOTE: this is not fully implemented yet, objects are still stored serialized. What works * Document storage * Classes and Objects * Attachments * Links and Locks * Basic querying with JDOQL What doesn't work * Querying inside of objects * JPQL/XWQL queries * Document history * Permissions (requires unimplemented queries) * The feature you want I am interested in what the community thinks is the first priority, I can work on performance which will likely lead to patches being merged into master which will benefit everyone or I can work on more features which will benefit people who want to use XWiki as a traditional application wiki but use it on top of Cassandra. You can reply here or add comments to the wiki ;) Caleb