Replicated Data Management in Mobile Environments: Anything New Under the Sun?

Abstract

1 Replicated Data Management in Mobile Environments: Anything New Under the Sun? Daniel Barbar a-Mill a a and Hector Garcia-Molina b a M.I.T.L. 2 Research Way, Princeton, N.J. 08540. USA b Stanford University Department of Computer Science Stanford, CA 94305. USA The mobile wireless computing environment of the future will contain large numbers of low powered palmtop machines. In a mobile environment it is important to have dynamic replicated data management algorithms that allow for instance copies to migrate from one site to another or for new copies to be generated. In this paper we show that such dynamic algorithms can be obtained simply by letting transaction update the directory that specifies sites holding copies. Thus we argue that no fundamentally new algorithms are needed to cope with mobility. However, exisiting algorithms may have to be "tuned" for a mobile environment, and we discuss what this may entail. 1. Introduction The mobile wireless computing environment of the future [13] will contain large numbers of low powered palmtop machines, querying databases over wireless channels. The units will often be disconnected due to power limitations, inaccessible communication channels, or as units move between different cells. The ability to replicate data objects in such an environment will be essential. Object copies are the key to high data availability: when a unit is disconnected it can continue to process objects stored locally. At the same time, replicated data can improve performance: a copy at a nearby or less congested site can be accessed. Thus, we expect copies to be common both on mobile units as well as on the servers they interact with; these copies will be dynamically created, updated, and destroyed in the course of the system's operation. There are two fundamental problems related to replicated data in a mobile environment: How to manage the replicated data, providing the levels of consistency, durability and availability needed. How to loc