| Distributed systems are widely used today and gaining popularity with the advance of technology. It is important that distributed systems support replication in order to improve performance, availability and reliability. As the size of a distributed system increases, so does the number of users and applications in the system. One of the most important design issues related to replication is the selection of suitable mechanisms for various users and applications. The appropriate replication mechanisms depend on access patterns, frequency of updates, tolerance of data inconsistency, and other characteristics. A single replication mechanism cannot meet the needs of all applications and users in a distributed system because some applications, such as an online transaction processing, need near-real-time data consistency while other applications, such as email can tolerate inconsistency. Therefore distributed systems must be able to support a variety of replication mechanisms at the same time.; The goal of this dissertation was to build a flexible framework for different replication mechanisms in distributed systems that would be suitable for a wide variety of users and applications. A framework was developed that supports multiple replication mechanisms, allows different objects to be maintained with different replication mechanisms, and enables application programmers to provide their own replication mechanisms. The Prospero Replication System (PRS) was implemented on top of Prospero. Simulation results show that the PRS has better data availability and system performance than other systems. It will be argued that this framework allows the needs of diverse users and applications in large distributed systems to be met. This dissertation has produced two significant contributions. First, after an examination of replication mechanisms used in distributed systems, a flexible framework that supports multiple replication mechanisms together was designed and developed. Second, following an examination of different levels of replication between replicas and caches, a unified framework for them was produced. This multi-level replication allows the framework to work well with mobile computing by placing different replicas on mobile sites. |
