Semi-synchronous coordination scheme for distributed groupwork environments : SECTRA

Abstract

In this thesis, we present a new coordination scheme, named SECTRA (SEmi-synchronous Cooperative TRAnsaction), in order to coordinate cooperative activities in distributed groupwork environments. SECTRA is based on a group database model in which shared objects are hierarchically organized, and a two-layer transaction model where each layer represents a groupwork of a set of users and each user``s activities, respectively. Unlike the previous approaches for coordinating cooperative activities, SECTRA is able to be tuned to different requirements of various groupwork environments without sacrificing concurrency. This is achieved by the notion of demand notification and a flexible concurrency control mechanism called dynamic multi-granularity locking (DMGL). In demand notification, one user``s activities are notified to other users conditionally based on each user``s working set and the granularity of such notification can be tailored according to the requirements of a group. DMGL adopts multi-granularity locks to minimize locking overhead, but those locks can be dynamically reconfigured in case of access conflicts in order to support a high degree of concurrency.