Neo4j implements a caching mechanism that stores nodes and relationships as useful, internal objects for rapid in-memory access. It also makes extensive use of the java.nio package, where native I/O is utilized to use memory outside the Java heap for mapped memory. Least Recently Used (LRU) is one of the simplest and most popular algorithms for implementation and rapid operations for caching needs. The Java-specific implementation makes use of the SoftReference and WeakReference objects, which are treated in a special manner by the garbage collector for memory reclamation. This principle is utilized in caches that grow rapidly to fill the heap but, when the demand for memory arises for more important tasks, reclamation takes place. So, there are no hard upper limits to caching of objects, while simultaneously making memory available for other operations. Neo4j caches work on this principle by default.