Understanding Degrees of Isolation

这项研究致力于使原子事务在广域分布式系统中运行良好，这将是未来的标准。这项工作的重点是对弱于可序列化的一致性级别的支持；这些级别之所以令人感兴趣，是因为许多应用程序不需要完全的可序列化，并且可以通过在较弱的级别上运行来实现更好的性能。过去已经定义了一些一致性级别，但早期的定义并不充分，因为它们要么不排除不需要的行为，要么不必要地限制实现技术。特别是，他们不允许乐观的技术，这是不幸的，因为这些是最好的广域和移动系统。这项研究提供了现有级别的定义，这些级别既有足够的限制来排除不良行为，也有足够的许可来允许广泛的并发控制机制。此外，该研究还定义了一些有用的新水平。此外，研究开发了弱级别的乐观实现，并使用模拟和实现来调查在较弱级别运行可以获得的性能优势。这项研究将导致对新旧薄弱级别的准确定义，得出一套新的、乐观的级别实现，并彻底理解较弱级别带来的性能好处。Http://www.pmg.lcs.mit.edu

This research is concerned with making atomic transactions perform well in the wide-area distributed systems that will be the norm in the future. The work focuses on support for consistency levels that are weaker than serializability; these levels are of interest because many applications do not require full serializability and can achieve better performance by running at weaker levels. Some consistency levels have been defined in the past, but the earlier definitions are inadequate because they either do not rule out undesirable behaviors, or they limit implementation techniques unnecessarily. In particular they do not allow optimistic techniques, which is unfortunate because these are the best for wide area and mobile systems. This research provides definitions of existing levels that are both constrained enough to rule out bad behaviors and permissive enough to allow a wide range of concurrency control mechanisms. In addition the research defines a number of useful new levels. Furthermore, the research develops optimistic implementations of the weak levels, and uses simulation and implementation to investigate the performance advantages that can be achieved by running at weaker levels. The research will lead to precise definitions of new and old weak levels, to a set of new, optimistic implementations of the levels, and to a thorough understanding of the performance benefits that derive from weaker levels. http://www.pmg.lcs.mit.edu