Got Predictability?: Experiences With Fault-Tolerant Middleware

Unpredictability in COTS-based systems often manifests as occasional instances of uncontrollably-high response times. A particular category of COTS systems, Fault-Tolerant (FT) middleware, is used in critical enterprise and embedded applications where predictability is of paramount importance. This paper presents empirical data, from 7 different three-tier, FT-middleware applications, that shows strong evidence supporting this "Magical 1%" hypothesis. They conducted a controlled experiment with 7 teams of students from a graduate-level course at Carnegie Mellon University. Each team, starting from a common three-tier architecture, independently implemented and evaluated an original application using middleware (either CORBA or EJB) and a custom-implemented fault-tolerance mechanism (relying on either state-machine or primary-backup replication) for the middle-tier server.