If your gear needs to store data persistently, you may use EJBs or configure a SQL Repository and then access the repository via JNDI in Nucleus.
Most deployments will have multiple application servers running to distribute the user load. Your gears must ensure data consistency and integrity between the repositories in each server. This can be accomplished by implementing optimistic locking using the version property or by setting an explicit cache integrity mode. See the SQL Repository Caching chapter in the Repository Guide.
