Question: What is Shenandoah: A Low-Pause-Time Garbage Collector in Java 15?

Just like ZGC, Shenandoah promises minimal pause times, regardless of the heap size.

You can read about exactly how Shenandoah achieves this on the Shenandoah wiki.

You can activate Shenandoah with the following VM option:

-XX:+UseShenandoahGC

Just like G1 and ZGC, Shenandoah returns unused memory to the operating system after a while.

There is currently no support for NUMA and SoftMaxHeapSize; however, at least NUMA support is planned.