Reduction of Unnecessarily Ordered Event Messages in Peer-to-Peer Model of Topic-Based Publish/Subscribe Systems
Hiroki Nakayama, Dilawaer Duolikun, Tomoya Enokido, Makoto Takizawa · 2016
A distributed system is considered in an event-driven model where a state of a process transits on occurrence of an event. In this paper, we discuss a peer-to-peer topic-based publish/subscribe (P2PPS) model where each peer process (peer) can both subscribe and publish event messages. The subscriptions and publications are specified in terms of topics. Each event message e carries a vector e:TV = (tv1, , tvh) of topics t1, , th in a system. An event message e1 causally precedes an event message e2 with respect to a topic subset T iff not only e1 causally precedes e2 but also e1.tvj ≤ e2.tvj for every topic tj in an intersection T of the publications of e1 and e2 and the subscription Si of pi. A pair of event messages e1 and e2 are unnecessarily ordered if e1.TV ≤ e2.TV but e1 does not causally precede e2. In this paper, we newly propose a topic-based-causally delivering (TBC) protocol where the linear clock and physical clock are used with topic vectors to reduce the number of pairs of messages unnecessarily ordered. We evaluate the TBC protocol and show the number of pairs of unnecessarily ordered messages is reduced.