Clustering has become an important means to analyze large datasets when labeled data is not available. The volume of data and its variety however challenge classical clustering algorithms, with density-based ones suffering from severe scalability issues.In this paper, we propose a way to perform density-based clustering efficiently by exploiting the horizontal scalability offered by big data solution such as Apache Spark. We are motivated by recent techniques for Internet monitoring that rely on clustering to group similar events and spot anomalies. We focus specifically on textual data, such as URLs or server logs. Computing the distance between points, here represented as strings, becomes a major issue. Indeed, when datasets become large, most of density-based clustering algorithms are bottlenecked by the computation of all the distances between any pairs of elements. To overcome this, we propose to decouple the distance computation, easily amenable to parallelization, from the algorithm execution. By using this approach, we can easily exploit the benefits of distributed platforms like Apache Spark or MapReduce. A faster execution of the algorithms is thus guaranteed, together with more flexibility in the choice of the clustering method.We make both the code and the dataset publicly available, to both guarantee the repeatability of the experiments, and possibly offering a new benchmark dataset.
