Duplicate Removal in Information Dissemination

Our experience with the SIFT [YGM95] information dissemination system (in use by over 7,000 users daily) has identi ed an important and generic dissemination problem: duplicate information. In this paper we explain why duplicates arise, we quantify the problem, and we discuss why it impairs information dissemination. We then propose a Duplicate RemovalModule (DRM) for an information dissemination system. The removal of duplicates operates on a per user, per document basis { each document read by a user generates a request, or a duplicate restraint. In wide-area environments, the number of restraints handled is very large. We consider the implementation of a DRM, examining alternative algorithms and data structures that may be used. We present a performance evaluation of the alternatives and answer important design questions such as: Which implementation is the best? With \best" scheme, how expensive will duplicate removal be? How much memory is required? How fast can restraints be processed?