For most systems, mapdb not much value, and increased costs. But for example, if the cache a huge number with ten GB level, or occupy the entire JVM 1/2 or more, the value of mapdb will be reflected. As its official website:
MapDB provides Java Maps, Sets, Lists, Queues and other collections backed by off-heap or on-disk storage. It is a hybrid between java collection framework and embedded database engine.
After using MapDB memory map, jvm gc pressure will be greatly reduced.
Specific use of reference: http: //www.mapdb.org/down/mapdb-manual-20.pdf