Minecraft used to have a vector pool as well and in some cases forced you to allocate Vector3s from there, to reduce garbage collection. That has since been eliminated.BlockPos, as I understand, forces large numbers of temporary objects that fill the eden space very quickly, resulting in large numbers of small collections. This in turn causes the number of small collections that an object survives to cross the threshold of promotion faster; this in turn generates more premature promotion into tenured of junk that should never last that long.