  The importance of real-time notification has been growing for social services
and Intelligent Transporting System (ITS). As an advanced version of Pub/Sub
systems, publish-process-subscribe systems, where published messages are
spooled and processed on edge servers, have been proposed to achieve
data-driven intelligent notifications. In this paper, we present a system that
allows a topic to be managed on multiple edge servers so that messages are
processed near the publishers, even when publishers are spread over a wide
area. Duplicating messages on geographically distributed servers could enable
immediate notification to neighboring subscribers. However, the duplicated
message spool may cause exhaustion of resources. We prepare a formal model of
our publish-process-subscribe system and formulate the topic allocation as an
optimization problem under the resource constraints of edge servers. As the
optimization problem is NP-hard, we propose heuristics leveraging the locality
and the pub/sub relationships observed between clients to use the edge server
resources efficiently. Our performance evaluation shows that our method reduces
the delay to deliver notifications and the effectiveness of the strategy
exploiting the relationships between clients.
