分布式键值存储中一致性-延迟权衡的表征与适应
Characterizing and Adapting the Consistency-Latency Tradeoff in Distributed Key-value Stores
摘要：
CAP定理是适用于分布式存储系统的基本结果。在本文中，我们首先提出并证明了两个类CAP不可能定理。为了说明这些定理，我们提出了概率模型来描述CAP定理的三个重要元素：一致性（C），可用性或延迟（A）和分区容差（P）。这些定理显示了无法实现的包络，即，这三个模型的参数的组合使得它们不可能一起实现。接下来，我们提出了一类称为PCAP的系统的设计，其性能接近我们的定理所描述的包络。此外，这些系统允许在单个数据中心上运行的应用程序指定延迟SLA或一致性SLA。PCAP系统自动适应，实时和不断变化的网络条件下，以满足SLA，同时优化其他C/A指标。我们将PCAP合并到两个流行的键值存储中- Apache Cassandra和Riak。我们的实验与这两个部署，在现实的工作负载下，显示PCAP系统令人满意地满足SLA，并执行接近可实现的信封。我们还将PCAP从单个数据中心扩展到多个地理分布的数据中心。
英文摘要：
The CAP theorem is a fundamental result that applies to distributed storage systems. In this paper, we first present and prove two CAP-like impossibility theorems. To state these theorems, we present probabilistic models to characterize the three important elements of the CAP theorem: consistency (C), availability or latency (A), and partition tolerance (P). The theorems show the un-achievable envelope, i.e., which combinations of the parameters of the three models make them impossible to achieve together. Next, we present the design of a class of systems called PCAP that perform close to the envelope described by our theorems. In addition, these systems allow applications running on a single data-center to specify either a latency SLA or a consistency SLA. The PCAP systems automatically adapt, in real-time and under changing network conditions, to meet the SLA while optimizing the other C/A metric. We incorporate PCAP into two popular key-value stores -- Apache Cassandra and Riak. Our experiments with these two deployments, under realistic workloads, reveal that the PCAP system satisfactorily meets SLAs, and performs close to the achievable envelope. We also extend PCAP from a single data-center to multiple geo-distributed data-centers.
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