Preferred backends
Many backends can be used for Jena. But only the Derby (or Hypersonic for Nuxeo 5.1 instances) and PostgreSQL backends are recommended. There are problems or special configurations that make for example MySQL or Oracle less easy to use.
Database corruption
Database corruption can happen with Jena. This can especially occur when there are inconsistencies in character encodings used between the application and the database. All the communications should be done in UTF-8.
Since corruption might happen it is mandatory to do data backups very often to be able to rollback to the latest state in which the database was not corrupted.
Here is below an exception you might get, this means that the database might be corrupted:
Once the database is corrupted, the only choice is often to reinitialize the tables used by Jena in the backend.
To reinitialize Jena, one only needs to destroy the used tables. But beware, all the data related to the relations will be lost. The exact procedure is the following:
- Stop Nuxeo
- Destroy all the tables related to Jena in the database backend. The tables used by Jena are those whose name starts with "jena". You need to do so at the backend database level, so for example directly at the PostgreSQL level. This cannot be done at the Nuxeo level.
- Restart Nuxeo. The needed tables will then be recreated again at startup. Note that those tables are only recreated at startup time and not seamlessly when needed.