Cluster of ObjectContainers / Federation:
(Maik can provide more details)

Customer needs to rollover their database containers at regular intervals determined by user needs (file size or time based) and to split meta-data from mass-data in different containers. So db4o needs to provide some kind of transactional clustering with N-phase-commits / locks / hot-backups and so on. There's some rudimentary cluster-support for queries already in db4o, but they'll need definitively a more complex solution. Additionally they'll need some kind of blazing-fast cross-references between ObjectContainers. Objectivity does this very well (and is amazing fast connecting objects between different containers)."

https://na2.salesforce.com/00T4000000WOZuE