And, of course, even G1 does not fill all memory before it starts collecting. Even generational GCs before G1 divide memory into smaller areas and try to collec

And, of course, even G1 does not fill all memory before it starts collecting. Even generational GCs before G1 divide memory into smaller areas and try to collect garbage quickly to get rid of short lived objects, so we're speaking about Java 6 timeframe. Example from my real world server - most of objects are collected at young generation, so gc costs are minimal, very few objects get promoted to old generation and full GC runs are very sporadic (and they are sub 1sec).