Adaptive Distributed RDF Graph Fragmentation and Allocation based on Query Workload

As massive volumes of Resource Description Framework (RDF) data are growing, designing a distributed RDF database system to manage them is necessary. In designing this system, it is very common to partition the RDF data into some parts, called fragments, which are then distributed. Thus, the distribution design comprises two steps: fragmentation and allocation. In this study, we explore the workload for fragmentation and allocation, which aims to reduce the communication cost during SPARQL query processing. Specifically, we adaptively maintain some frequent access patterns (FAPs) to reflect the characteristics of the workload while ensuring the data integrity and approximation ratio. Based on these frequent access patterns, we propose three fragmentation strategies, namely vertical, horizontal, and mixed fragmentation, to divide RDF graphs while meeting different types of query processing objectives. After fragmentation, we discuss how to allocate these fragments to various sites while balancing the fragments. Finally, we discuss how to process queries based on the results of fragmentation and allocation. Experiments over large RDF datasets confirm the superior performance of our proposed solutions.