During some bug fixing of the Drools' Rete implementation I discoverd the need for an Object repository for fact retrieval via the FactHandle id. Being painfully aware of how much HashMaps are killing Drools performance and creating issues with garbage collection I searched for alternative implementations - pcj, trove and colt, commons-collections does not offer a primitive map - and benchmarked those against my own specialised implementation - the results, especially for memory, proved interesting.