The DLR-ORECOP real-time replication control protocol

Many real-time applications need data services in distributed environments. Providing such data services is a challeging task due to long remote data accessing delays and stringent time requirements of real-time transactions. In this paper, we use data replication in distributed real-time database systems in order to improve meeting these stringent requirements and fault tolerance . We propose an optimistic replication control protocol, called DLR-ORECOP (dynamic level of replication with optimistic replication conntrol protocol), which finds a trade-off between updating replicas and meeting user transactions deadlines. We introduce a list, called list of available copies (LAC), associated with each data item in the database which contains the identifiers of the most updated replicas. Fault tolerance is provided by building LACs dynamically according to transactions executions and system load, giving then the real-time database a dynamic level of replication. The experimental results show that among the replication control protocols evaluated, DLR-ORECOP provides the best performance for a variety of workloads and system configurations. In addition, the experimental results show that DLR-ORECOP performances are not significantly affected by the loss of update messages.