APART: Low cost active replication for multi-tier data acquisition systems

This paper proposes APART (A Posteriori Active ReplicaTion), a novel active replication protocol specifically tailored for multi-tier data acquisition systems. Unlike existing active replication solutions, APART does not rely on a-priori coordination schemes determining a same schedule of events across all the replicas, but it ensures replicas consistency by means of an a-posteriori reconciliation phase. The latter is triggered only in case the replicated servers externalize their state by producing an output event towards a different tier. On one hand, this allows coping with non-deterministic replicas, unlike existing active replication approaches. On the other hand, it allows attaining striking performance gains in the case of silent replicated servers, which only sporadically, yet unpredictably, produce output events in response to the receipt of a (possibly large) volume of input messages. This is a common scenario in data acquisition systems, where sink processes, which filter and/or correlate incoming sensor data, produce output messages only if some application relevant event is detected. Further, the APART replica reconciliation scheme is extremely lightweight as it exploits the cross-tier communication pattern spontaneously induced by the application logic to avoid explicit replicas coordination messages. © 2008 IEEE.