The Weakest Failure Detector for Genuine Atomic Multicast

Atomic broadcast is a group communication primitive to order messages across a set of distributed processes. Atomic multicast is its natural generalization where each message m is addressed to dst(m), a subset of the processes called its destination group. A solution to atomic multicast is genuine when a process takes steps only if a message is addressed to it. Genuine solutions are the ones used in practice because they have better performance. Let ? be all the destination groups and ? be the cyclic families in it, that is the subsets of ? whose intersection graph is hamiltonian. This paper establishes that the weakest failure detector to solve genuine atomic multicast is ? = (?_{g,h ? ?} ?_{g ? h}) ? (?_{g ? ?} ?_g) ? ?, where ?_P and ?_P are the quorum and leader failure detectors restricted to the processes in P, and ? is a new failure detector that informs the processes in a cyclic family f ? ? when f is faulty. We also study two classical variations of atomic multicast. The first variation requires that message delivery follows the real-time order. In this case, ? must be strengthened with 1^{g ? h}, the indicator failure detector that informs each process in g ? h when g ? h is faulty. The second variation requires a message to be delivered when the destination group runs in isolation. We prove that its weakest failure detector is at least ? ? (?_{g, h ? ?} ?_{g ? h}). This value is attained when ? = ?

Testing the dependability and performance of group communication based database replication protocols

Database replication based on group communication systems has recently been proposed as an efficient and resilient solution for large-scale data management. However, its evaluation has been conducted either on simplistic simulation models, which fail to assess concrete implementations, or on complete system implementations which are costly to test with realistic large-scale scenarios. This paper presents a tool that combines implementations of replication and communication protocols under study with simulated network, database engine, and traffic generator models. Replication components can therefore be subjected to realistic large scale loads in a variety of scenarios, including fault-injection, while at the same time providing global observation and control. The paper shows first how the model is configured and validated to closely reproduce the behavior of a real system, and then how it is applied, allowing us to derive interesting conclusions both on replication and communication protocols and on their implementationsFundação para a Ciência e a Tecnologia (FCT) - Project STRONGREP (POSI/CHS/41285/2001)