Fabian E. Bustamante, Patrick Widener and Karsten Schwan

College of Computing
Georgia Institute of Technology
Atlanta, GA 30332, USA
{fabianb, pmw, schwan}@cc.gatech.edu

Abstract

Technology advances and increasing end-user expectations of distributed applications pose scalability challenges for directory services and consistency challenges for their clients. In particular, the number of objects, the number of attributes per object, and the rate of change of both objects and attributes are increasing. At the same time, context-aware applications such as active portals require that the data they obtain from directories be highly consistent.
We argue that traditional pull-based interfaces to directory services are insufficiently scalable for both clients and servers, and propose a complementary proactive (push-based) interface. We describe the design and implementation of a directory service with such an interface, the Proactive Directory Service (PDS), and compare its performance against off-the-shelf implementations of DNS and the Lightweight Directory Access Protocol.
Our experiments show that maintaining a high degree of consistency through a strictly pull-based interface may impose intolerable high loads on clients, servers, and the network, depending on the rate of change of the object(s) involved. By making the degree of consistency of the client data independent of the frequency with which it is updated, a proactive interface allows applications to obtain a perfect degree of consistency with a reasonable load on resources.

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