Document Nearest Neighbors Query Based on Pairwise Similarity with MapReduce.

With the continuous development of Web technology, many Internet issues evolve into Big Data problems, characterized by volume, variety, velocity and variability. Among them, how to organize plenty of web pages and retrieval information needed is a critical one. An important notion is document classification, in which nearest neighbors query is the key issue to be solved. Most parallel nearest neighbors query methods adopt Cartesian Product between training set and testing set resulting in poor time efficiency. In this paper, two methods are proposed on document nearest neighbor query based on pairwise similarity, i.e. brute-force and pre-filtering. brute-force is constituted by two phases (i.e. copying and filtering) and one map-reduce procedure is conducted. In order to obtain nearest neighbors for each document, each document pair is copied twice and all records generated are shuffled. However, time efficiency of shuffle is sensitive to the number of the intermediate results. For the purpose of intermediate results reduction, pre-filtering is proposed for nearest neighbor query based on pairwise similarity. Since only first top-k neighbors are output for each document, the size of records shuffled is kept in the same magnitude as input size in pre-filtering. Additionally, detailed theoretical analysis is provided. The performance of the algorithms is demonstrated by experiments on real world dataset.