But if I'm reading it correctly GO GC will actually rely on a using a lot of memory to ensure it can hit the pause time goal. As far as I understand copying/ge

But if I'm reading it correctly GO GC will actually rely on a using a lot of memory to ensure it can hit the pause time goal. As far as I understand copying/generational collector by themselves don't add a lot of memory overhead. They simply add more complexity. You tend to require a lot more memory to ensure most your allocation & allocation happens in nursery (which can be scary fast and low overhead) and to allow the old generation GC to pace itself. I wonder how much of the 20% expected GC overhead comes from the fact that they can't do the nursery GC optimisation and whats the expected overhead when it goes generational in 1.6 One thing I absolutely hate with CMS is the fallback single thread collector for Old Gen that makes for a scary possibility. Don't think GO will have one of those which is nice to see (not for me though :().