I told that we have 4 Series .. Parallel.. CMS and G1 and G1 is default. I did not know the detail but i knew that GC runs in thread and stop execution of application . But this guy was more interested in internals of GC . I politely said i do not know. But again he was behaving that i have done a crime.His tone was simply insulting. Dude we are not judging memory of people.