Towards a Scalable, Distributed Metadata Service for Causal Consistency under Partial Geo-replication
Towards a Scalable, Distributed Metadata Service for Causal Consistency under Partial Geo-replication
复制标题
实现部分地理复制下因果一致性的可扩展、分布式元数据服务
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
P. V. Roy
中科院分区：
文献类型：
--
作者：
Manuel Bravo;L. Rodrigues;P. V. Roy
因果一致性是在地理复制设置中具有实际意义的一致性标准，因为它以可扩展的方式提供了定义良好的语义。事实上，已经证明因果一致性是可以在始终可用的系统中实施的最强一致性模型。以前的方法来提供因果一致性，成功地解决了这个问题下的完全地理复制，揭示了固有的权衡之间的并发性，系统允许和强制执行因果关系所需的元数据的大小。当元数据被压缩时，关于并发性的信息可能丢失，从而产生假依赖性，即，编码可能暗示了现实中不存在的因果关系。假依赖性可能会导致处理请求时的人为延迟，并降低客户端体验的服务质量。然而，是否有可能设计一个可扩展的解决方案，只使用几乎可以忽略不计的元数据量，它仍然能够实现高水平的并发下部分地理复制，越来越相关的设置，仍然是一个具有挑战性和有趣的开放研究问题。这份立场文件报告了Saturn的持续发展，Saturn是一种用于地理复制系统的元数据服务，旨在减轻虚假依赖关系的影响，同时保持元数据的大小较小（即使对于具有挑战性的设置，如部分地理复制）。
Causal consistency is a consistency criteria of practical relevance in geo-replicated settings because it provides well-defined semantics in a scalable manner. In fact, it has been proved that causal consistency is the strongest consistency model that can be enforced in an always-available system. Previous approaches to provide causal consistency, which successfully tackle the problem under full geo-replication, have unveiled the inherent tradeoff between the concurrency that the system allows and the size of the metadata needed to enforce causality. When the metadata is compressed, information about concurrency may be lost, creating false dependencies, i.e., the encoding may suggest a causal relation that does not exist in reality. False dependencies may cause artificial delays when processing requests, and decrease the quality of service experienced by the clients. Nevertheless, whether is possible to design a scalable solution that only uses an almost negligible amount of metadata and it is still capable of achieving high levels of concurrency under partial geo-replication, an increasingly relevant setting, remains as a challenging and interesting open research question. This position paper reports on the on-going development of Saturn, a metadata service for geo-replicated systems, that aims at mitigating the effects of false dependencies while keeping the metadata size small (even for challenging settings as partial geo-replication).