The estimation of the frequency of the elements on a set is needed in a wide range of computing applications. For example, to estimate the number of hits that a video gets or the number of packets in a network flow. In some cases, the number of elements in the set is very large and it is not practical to maintain a table with the exact count for each of them. Instead, simpler and more efficient data structures, commonly referred to as sketches, that provide an estimate are used. Among those structures the Count Min Sketch (CMS) is one of the most popular sketches. The CMS provides estimates that have one sided errors. In more detail, the CMS returns an estimate that is equal to or larger than the actual value. An update or check requires a small and constant number of memory accesses and the memory footprint is fixed and does not depend on the number of elements. The CMS relies on several arrays of counters that are stored in memory. Memories are prone to suffer soft errors that flip the contents of memory cells due for example to ionizing radiation. Therefore, it is of interest to study the impact that soft errors can have on the CMS estimates and to propose protection techniques that minimize their effect while requiring low overhead in terms of additional memory and circuitry. To the best of our knowledge this has not been done before. In this article, first the effect of soft errors on the CMS is evaluated by injecting errors. Then, in the second part a protection technique that does not require additional memory bits is presented and compared with the protection using a parity bit. In the last part of the article, the technique is extended to protect also against double adjacent bit errors.

中文翻译：

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软容错计数最小草图

在广泛的计算应用程序中需要估计集合中元素的频率。例如，估计视频获得的点击次数或网络流中的数据包数量。在某些情况下，集合中的元素数量非常大，并且维护一个包含每个元素的精确计数的表是不切实际的。相反，使用更简单和更有效的数据结构，通常称为草图，提供估计。在这些结构中，Count Min Sketch (CMS) 是最受欢迎的草图之一。CMS 提供具有单方面错误的估计。更详细地说，CMS 返回的估计值等于或大于实际值。更新或检查需要少量且恒定的内存访问次数，并且内存占用是固定的，不依赖于元素的数量。CMS 依赖于存储在内存中的多个计数器数组。存储器容易出现软错误，例如由于电离辐射而翻转存储器单元的内容。因此，研究软错误可能对 CMS 估计产生的影响并提出保护技术，以最大限度地减少其影响，同时在额外的存储器和电路方面需要低开销是很有意义的。据我们所知，这是以前没有做过的。在本文中，首先通过注入错误来评估软错误对 CMS 的影响。然后，在第二部分中，介绍了一种不需要额外存储位的保护技术，并与使用奇偶校验位的保护进行了比较。在文章的最后一部分，该技术被扩展以防止出现双相邻位错误。