Distributed Garbage Collection for Wide Area Replicated Memory

It is well known that distributed systems pose serious difficulties concerning memory management: when done manually, it leads to memory leaks and dangling references causing applications to fail. We address this problem by presenting a distributed garbage collection (DGC) algorithm for distributed systems supporting replicated data over wide area networks. Current DGC algorithms are not well suited for such systems because either (i) they do not consider the existence of replication, or (ii) they impose severe constraints on scalability by requiring causal delivery to be provided by the underlying communication layer. Our algorithm solves these problems by (i) adapting classical reference-counting DGC algorithms that were conceived for non-replicated systems (e.g. indirect reference-counting, SSP chains, etc.), and (ii) improving our previous algorithm for replicated systems (i.e. Larchant). The result is a DGC algorithm that, besides being correct in presence of replicated data and independent of the protocol that maintains such replicas coherent among processes, it does not require causal delivery to be ensured by the underlying communications support. In addition, it has minimal performance impact on applications.