基于局部性和可用性的分布式存储代码的下载时间分析
Download Time Analysis for Distributed Storage Codes with Locality and Availability
摘要：
本文介绍了技术分析预期的下载时间在分布式存储系统，采用系统的可用性代码。通过这些代码，可以通过包含对象和多个恢复组的系统服务器访问热数据。当收到对象请求时，可以将其复制（分叉）到系统服务器和所有恢复组。我们首先考虑低流量的制度，并提出了封闭形式的表达式的下载时间。通过比较系统的可用性，最大距离可分离（MDS），和复制代码，我们证明了可用性代码可以减少下载时间在某些设置中，但并不总是最佳的。在高流量状态下，系统由多个相互依赖的Fork-Join队列组成，使得精确分析变得困难。因此，我们提出了上界和下界的下载时间，和M/G/1队列近似几种情况下的利益。通过大量的数值模拟，我们评估我们的界限，并证明了M/G/1队列近似具有很高的精度。
英文摘要：
The paper presents techniques for analyzing the expected download time in distributed storage systems that employ systematic availability codes. These codes provide access to hot data through the systematic server containing the object and multiple recovery groups. When a request for an object is received, it can be replicated (forked) to the systematic server and all recovery groups. We first consider the low-traffic regime and present the close-form expression for the download time. By comparison across systems with availability, maximum distance separable (MDS), and replication codes, we demonstrate that availability codes can reduce download time in some settings but are not always optimal. In the high-traffic regime, the system consists of multiple inter-dependent Fork-Join queues, making exact analysis intractable. Accordingly, we present upper and lower bounds on the download time, and an M/G/1 queue approximation for several cases of interest. Via extensive numerical simulations, we evaluate our bounds and demonstrate that the M/G/1 queue approximation has a high degree of accuracy.
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