The paper Evaluating Query and Storage Strategies for RDF Archives (J. D. Fernandez, J. Umbrich, A. Polleres, M. Knuth) studies how to measure the performance of RDF databases. HDTQ: Managing RDF Datasets in Compressed Space (J. D. Fernández, M. A. Martínez-Prieto, A. Polleres, J. Reindorf) presents a compact representation of RDF as 4-tuples that can be efficiently queried.
The first paper appears in the Semantic Web Journal (currently in press), the second will be presented in June at the Extended Semantic Web Conference (ESWC) 2018