WebSphere® eXtreme Scale is used to provide in-line caching for a database back-end or as a side cache for a database. In-line caching uses eXtreme Scale as the primary means for interacting with the data. When eXtreme Scale is used as a side cache, the back-end is used in conjunction with the eXtreme Scale.
eXtreme Scale can be used as a side-cache for an application's data access layer. In this scenario, eXtreme Scale is used to temporarily store objects that would normally be retrieved from a back-end database. Applications check to see if eXtreme Scale contains the desired data. If the data is there, the data is returned to the caller. If the data is not there, the data is retrieved from the back-end and inserted into eXtreme Scale so that the next request can use the cached copy. The following diagram illustrates how eXtreme Scale can be used as a side-cache using an arbitrary data access layer such as OpenJPA or Hibernate.
Side cache plug-ins for Hibernate and OpenJPA