Causally ordering delivery of event messages in P2PPSO systems

摘要

In topic-based PS (Publish/Subscribe) model, each peer process (peer) specifies subscription topics and publishes an event message with publication topics. A peer only receives an event message whose publication topics include some common topic with the subscription topics. In the P2PPSO (P2P (peer-to-peer) type of topic-based Publish/Subscribe with Object concept) model, each peer exchanges objects by publishing and receiving event messages with no centralized coordinator. Here, objects are denoted by topics and event messages are characterized by topics of the objects in the event messages. Suppose an event message e(j) published by a peer p(j) carries objects on some topics into a target peer p(i). Information, i.e. objects in the peer p(j) illegally flows to the peer p(i) if the peer p(i) is not allowed to subscribe the topics. An illegal object of a peer p(i) is an object whose topics the peer p(i) is not allowed to subscribe. In the TOBS (Topics-of- Objects-Based Synchronization) protocol, illegal objects are not delivered to target peers, but every event message is assumed to be causally delivered in the underlying network. In this paper, we newly propose a TOBSCO (TOBS with Causally Ordering delivery) protocol where the function to causally deliver every pair of event messages is added to the TOBS protocol. In the evaluation, we show every pair of event messages are causally delivered and it takes longer to deliver event messages in the TOBSCO protocol. (C) 2019 Elsevier B.V. All rights reserved.