Performance Evaluation of Main-Memory R-tree Variants

There have been several techniques proposed for improving the performance of main-memory spatial indexes, but there has not been a comparative study of their performance. In this paper we compare the performance of six main-memory R-tree variants: R-tree, R*-tree, Hilbert R-tree, CR-tree, CR*tree, and Hilbert CR-tree. CR*-trees and Hilbert CR-trees are respectively a natural extension of R*-trees and Hilbert R-trees by incorporating CR-trees’ quantized relative minimum bounding rectangle (QRMBR) technique. Additionally, we apply the optimistic, latch-free index traversal (OLFIT) concurrency control mechanism for B-trees to the R-tree variants while using the GiST-link technique. We perform extensive experiments in the two categories of sequential accesses and concurrent accesses, and pick the following best trees. In sequential accesses, CR*-trees are the best for search, Hilbert R-trees for update, and Hilbert CR-trees for a mixture of them. In concurrent accesses, Hilbert CR-trees for search if data is uniformly distributed, CR*-trees for search if data is skewed, Hilbert R-trees for update, and Hilbert CR-trees for a mixture of them. We also provide detailed observations of the experimental results, and rationalize them based on the characteristics of the individual trees. As far as we know, our work is the first comprehensive performance study of mainmemory R-tree variants. The results of our study provide a useful guideline in selecting the most suitable index structure in various cases.