On Frequency Estimation and Detection of Heavy Hitters in Data Streams

摘要

A stream can be thought of as a very large set of data, sometimes even infinite, which arrives sequentially and must be processed without the possibility of being stored. In fact, the memory available to the algorithm is limited and it is not possible to store the whole stream of data which is instead scanned upon arrival and summarized through a succinct data structure in order to maintain only the information of interest. Two of the main tasks related to data stream processing are frequency estimation and heavy hitter detection. The frequency estimation problem requires estimating the frequency of each item, that is the number of times or the weight with which each appears in the stream, while heavy hitter detection means the detection of all those items with a frequency higher than a fixed threshold. In this work we design and analyze ACMSS, an algorithm for frequency estimation and heavy hitter detection, and compare it against the state of the art AS ketch algorithm. We show that, given the same budgeted amount of memory, for the task of frequency estimation our algorithm outperforms AS ketch with regard to accuracy. Furthermore, we show that, under the assumptions stated by its authors, AS ketch may not be able to report all of the heavy hitters whilst ACMSS will provide with high probability the full list of heavy hitters.