A compressed internal representation of an inventory, to be transmitted with the various inventory update packets. Rather than use a List, we pool these Inventory instances to avoid generating significant amounts of garbage. For a popular server, it is perfectly reasonable to expect north of a gigabyte of memory to be wasted through List instances in the span of an hour. We eliminate all garbage generation by using soft-reference pooled inventory objects. While this does result in a small hit due to the synchronization involved, it is nothing compared to the hit caused by garbage collection and memory allocation involved with inventories.