• Source
    [Show abstract] [Hide abstract]
    ABSTRACT: One way to implement a fault-tolerant a service is by replicating it at sites that fail independently. One of the replication techniques is active replication where each request is executed by all the replicas. Thus, the effects of failures can be completely masked resulting in an increase of the service availability. In order to preserve consistency among replicas, replicas must exhibit a deterministic behavior, what has been traditionally achieved by restricting replicas to be singlethreaded. However, this approach cannot be applied in some setups, like transactional systems, where it is not admissible to process transactions sequentially. In this paper, we present a deterministic scheduling algorithm for multithreaded replicas in a transactional framework. To ensure replica determinism requests to replicated servers are submitted by means of reliable and totally ordered multicast. Internally, a deterministic scheduler ensures that all threads are scheduled in the same way at all replicas what guarantees replica consistency 1.
    08/2001;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Grid technologies have matured over the last few years. This level of maturity is especially true in the field of scientific computing in which Grids have become the main infrastructure for scientific problem solving. Due to its success, the use of Grid technology rapidly finds its introduction into other fields. One of such fields is enterprise computing in which Grids are seen as a new architecture for data centers. In this paper, we describe the vision of enterprise Grids, current scientific achievements that will leverage this vision, and challenges ahead.
    Journal of Grid Computing 01/2007; 5(3):283-294. · 1.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Middleware platforms are becoming very popular among system developers. Due to its popularity, there is an increasing demand for dependable middleware support. In the past few years several research efforts have concentrated in augmenting the dependability of middle-ware infrastructures which have led to the definition of the FT-Corba specification. Active replication is one of the main techniques that have been used to achieve some of the required dependability attributes such as high-availability. This kind of replication requires determin-istic replicas to behave as a state machine what has been traditionally achieved by restricting replicas to be single-threaded. Unfortunately, single-threading results too restrictive for mid-dleware servers, especially transactional ones, where it is not admissible to process requests sequentially. In this paper, we show how it is possible to remove this restriction. We present a deterministic scheduling algorithm for multithreaded replicas in a transactional framework. Determinism of multithreaded replicas is achieved with a combination of reliable total order multicast and a deterministic scheduler. The former guarantees that all the replicas see the external events in the same order. The latter, ensures that all threads are scheduled in the same way at all replicas. One of the novelties of the approach is that determinism is achieved without resorting to inter-replica communication. Additionally, the paper also addresses how to perform online recovery while maintaining replica determinism in order to keep a high level of availability. £ This paper consolidates results from the papers [1] and [2].