Model-Driven Comparison of State-Machine-Based and Deferred-Update Replication Schemes

In this paper, we analyze and experimentally compare state-machine-based and deferred-update (or transactional) replication, both relying on atomic broadcast. We define a model that describes the upper and lower bounds on the execution of concurrent requests by a service replicated using either scheme. The model is parametrized by the degree of parallelism in either scheme, the number of processor cores, and the type of requests. We analytically compared both schemes and a non-replicated service, considering a bcast- and request-execution-dominant workloads. To evaluate transactional replication experimentally, we developed Paxos STM---a novel fault-tolerant distributed software transactional memory with programming constructs for transaction creation, abort, and retry. For state-machine-based replication, we used JPaxos. Both systems share the same implementat ion of atomic broadcast based on the Paxos algorithm. We present the results of performance evaluation of both replication schemes, and a non-replicated (thus prone to failures) service, considering various workloads. The key result of our theoretical and experimental work is that neither system is superior in all cases. We discuss these results in the paper.