Broadcast and Epidemic Communication for Managing ReplicatedData

许多商业数据库产品和应用程序工具开始支持数据复制，以便在分布式、移动和断开连接的环境中提供对数据的随时访问。这些系统中的大多数都选择使用异步复制方案，其中对副本的更新是不同步的。尽管这些模式在单对象更新（例如，文件系统等环境）中执行得相当好，但当单个更新涉及多个对象（例如，事务环境）时，它们就不适合了。这个项目研究了使用同步和异步广播机制管理复制数据库的好处。广播原语，即可靠广播、因果广播和原子广播，将用于设计同步复制的新协议。在同步复制中，访问被复制数据的事务与系统中的其他事务同步。在异步复制中，事务在本地执行，并使用其他方法在全局传播其影响，以及检测和纠正不一致。这里将使用传播的流行模型作为传递机制。将开发悲观复制协议和乐观复制协议来异步维护副本。最后，将开发一个仿真框架来评估同步和异步复制的协议。

Many commercial database products and application tools are beginning to support data replication to provide ready access to data in distributed, mobile, and disconnected environments. Most of these systems have chosen to use asynchronous replication schemes in which updates to replicas are not synchronized. Although these schemes perform reasonably well for single object updates (i.e., environments such as file-systems), they are not suitable when a single update involves multiple objects (i.e., transactional environments). This project investigates the benefits of using synchronous and asynchronous broadcast mechanisms for managing replicated databases. Broadcast primitives, viz., reliable broadcast, causal broadcast, and atomic broadcast, will be used to design new protocols for synchronous replication. In synchronous replication, transactions accessing replicated data are synchronized with other transactions in the system. In asynchronous replication, transactions execute locally and other means are used to disseminate their effects globally as well as to detect and correct inconsistencies. The epidemic model of communication will be used as the transport mechanism here. Pessimistic as well as optimistic replication protocols will be developed to maintain replicas asynchronously. Finally, a simulation framework will be developed to evaluate the protocols for synchronous and asynchronous replication.