Adaptive Optimistic Total-Order Protocols for Wide-Area Database Replication

A total order broadcast protocol is a fundamental building block in the construction of many distributed faulttolerant applications. Informally, the purpose of such a protocol is to provide a communication primitive that allows processes to agree on the set of messages they deliver and, also, on their delivery order. Uniform total order broadcast is particularly useful to implement fault-tolerant services by using software-based replication [4]. Unfortunately, the implementation of such a primitive can be expensive both in terms of communication steps and number of messages exchanged. This problem is exacerbated in wide-area networks, where the performance of the algorithm may be limited by the presence of high-latency links. Several total order protocols have been proposed that use different strategies to offer good performance [3] however, there is no protocol that outperforms all others in all scenarios: each protocol offers best results under different load profiles and/or network conditions. This paper describes on-going research that is being performed in the context of the IST GORDA (Open Replication of DAtabases), 1 project that intends to foster database replication as a means to address the challenges of trust, integration, performance and cost in current database systems underlying the information society. The GORDA project has a mix of academic and industrial partners, including U. do Minho, U. della Svizzera Italiana, U. de Lisboa, INRIA Rhône-Alpes, Continuent, and MySQL AB. The paper addresses the following issues

A Metaprotocol Outline for Database Replication Adaptability

Abstract. Database replication tasks are accomplished with the aid of consistency protocols. Commonly, proposed solutions use a single replication protocol providing just one isolation level. The main drawback of this approach is its lack of flexibility for changing scenarios –i.e. workloads, access patterns... – or heterogeneous client application requirements. This work proposes a metaprotocol for supporting several replication protocols which use different replication techniques or provide different isolation levels. With this metaprotocol, replication protocols can either work concurrently with the same data or be sequenced for adapting to changing environments. In this line, the use of a load monitor would enable the best choice for each transaction, selecting the most appropriate protocol according to the current system characteristics. This paper is focused on outlining this metaprotocol design, establishing the metadata set needed and the required interaction between the main database replication protocol families.