The underlying reason is that at around 32GB the JVM internally shifts from 32bit pointers for HEAP management to 64bit. The feature is called compressed object

The underlying reason is that at around 32GB the JVM internally shifts from 32bit pointers for HEAP management to 64bit. The feature is called compressed object pointers (compressed oops) The increased pointer size uses substantial amounts of RAM, a reasonable estimate is that you need at least ~45GB to not have a loss in total available HEAP. Also, GC cycles get longer the more HEAP you have. However, some workloads may require more heap to even be possible and there’s pauseless garbage collector implementations able to handle substantial amounts of memory, so it is possible. It’s just not something you should be doing unless you know exactly what you are doing. See https://wiki.openjdk.java.net/display/HotSpot/CompressedOops https://wiki.openjdk.java.net/display/HotSpot/CompressedOops