Exploiting weak connectivity for mobile file access

TLDR

Weak connectivity, such as intermittent, low‑bandwidth, or expensive networks, is a common reality in mobile computing. This paper describes how the Coda File System has evolved to exploit such networks. The evolution introduces systematic adaptivity to remove hidden assumptions about strong connectivity, modifying communication, cache validation, update propagation, and cache‑miss handling. As a result, Coda delivers strong performance across bandwidths that vary over four orders of magnitude, from modem speeds to LAN speeds.

Abstract

Weak connectivity, in the form of intermittent, low-bandwidth, or expensive networks is a fact of life in mobile computing. In this paper, we describe how the Coda File System has evolved to exploit such networks. The underlying theme of this evolution has been the systematic introduction of adaptivity to eliminate hidden assumptions about strong connectivity. Many aspects of the system, including communication, cache validation, update propagation and cache miss handling have been modified. As a result, Coda is able to provide good performance even when network bandwidth varies over four orders of magnitude - from modem speeds to LAN speeds.