Scalable distributed data cube computation for large-scale multidimensional data analysis on a Spark cluster

Abstract

A data cube is a powerful analytical tool that stores all aggregate values over a set of dimensions. It provides users with a simple and efficient means of performing complex data analysis while assisting in decision making. Since the computation time for building a data cube is very large, however, efficient methods for reducing the data cube computation time are needed. Previous works have developed various algorithms for efficiently generating data cubes using MapReduce, which is a large-scale distributed parallel processing framework. However, MapReduce incurs the overhead of disk I/Os and network traffic. To overcome these MapReduce limitations, Spark was recently proposed as a memory-based parallel/distributed processing framework. It has attracted considerable research attention owing to its high performance. In this paper, we propose two algorithms for efficiently building data cubes. The algorithms fully leverage Spark’s mechanisms and properties: Resilient Distributed Top-Down Computation (RDTDC) and Resilient Distributed Bottom-Up Computation (RDBUC). The former is an algorithm for computing the components (i.e., cuboids) of a data cube in a top-down approach; the latter is a bottom-up approach. The RDTDC algorithm has three key functions. (1) It approximates the size of the cuboid using the cardinality without additional Spark action computation to determine the size of each cuboid during top-down computation. Thus, one cuboid can be computed from the upper cuboid of a smaller size. (2) It creates an execution plan that is optimized to input the smaller sized cuboid. (3) Lastly, it uses a method of reusing the result of the already computed cuboid by top-down computation and simultaneously computes the cuboid of several dimensions. In addition, we propose the RDBUC bottom-up algorithm in Spark, which is widely used in computing Iceberg cubes to maintain only cells satisfying a certain condition of minimum support. This algorithm incorporates two primary strategies: (1) reducing the input size to compute aggregate values for a dimension combination (e.g., A, B, and C) by removing the input, which does not satisfy the Iceberg cube condition at its lower dimension combination (e.g., A and B) computed earlier. (2) We use a lazy materialization strategy that computes every combination of dimensions using only transformation operations without any action operation. It then stores them in a single action operation. To prove the efficiency of the proposed algorithms using a lazy materialization strategy by employing only one action operation, we conducted extensive experiments. We compared them to the cube() function, a built-in cube computation library of Spark SQL. The results showed that the proposed RDTDC and RDBUC algorithms outperformed Spark SQL cube().