Lightweight Map, SortedMap, LinkedMap, Set, and SortedSet implementation(s) with minimal 3rd party dependencies that alleviates memory pressure by offloading to disk. Tested on Java 8, 11, and 17.
While there are other alternatives out there, they were almost too complicated. This is a simple way to drop-in as a replacement where you use JVM Maps or Sets and don't want to fuss with settings too much.
There are several implementations available, depending on your needs and runtime environment. We evaluated RocksDB, LevelDB (pure Java and JNI versions), MVStore, LMDB, KyotoCabinet, TokyoCabinet, and Tkrzw.
Based on our primary need for minimal memory usage (including a desire to not rely on memory-mapped files) and as small as possible dependencies, we narrowed in on the older, but still impressive TokyoCabinet vs. some of the more recent entrants like RocksDB.