An additional enhancement to G1 GC—to return the Java heap memory to the Operating System (OS) when idle. This enhancement is most likely to be triggered by the increase in container environments that are used to run applications on the JVM.

Prior to Java 12, G1 returned memory from the Java heap in two cases—while performing a full GC or during a concurrent cycle. However, neither of these instances happen very often. In fact, G1 performs a full GC as its last resort to free up memory. A concurrent cycle is subjected to the Java heap allocation and occupancy.

This GC behavior has multiple disadvantages—organizations pay more for the memory even though it isn't used in an efficient manner in container environments, and service providers under-utilize their resources. In this enhancement, the JVM determines the idle times for an application and returns the memory to the OS. This makes a lot of sense since the usage of applications isn't the same across the days of the week or even hours of a day. This enhancement can save organizations a lot of money when deploying their application to environments that provide resources as a service.