Configuring on a AdvancedCacheLoader preload=true and asyn=true cause it to load each entry in the store in a loop, each entry being loaded through an store read.
This is caused by the way loadAll is implemented in the AsynLoader: in order to enforce consistency with whatever is in memory it does some special handling. The thing is, though, that we don't need this advanced async loader logic during the initial preload, as the async cache loader is empty.