Does g1 collect all (both eden and survivor) or part of garbages in young gc?

Question

I am curious if g1 will choose part of young region to collect in order to reach the target gc time. And what the real meaning of params InitiatingHeapOccupancyPercent?

Answer 1

In G1 GC, heap is divided into different regions. To achieve the target GC time number of regions will be altered accordingly. From logs you can observe variations in Young generation size. InitiatingHeapOccupancyPercent indicates when to start GC cycles. By default it's 45. That means once heap is 45% full then GC cycles will kick in. Reference: https://www.oracle.com/technetwork/tutorials/tutorials-1876574.html