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Flash-based SSDs have become well established in the storage market, replacing magnetic disks in both enterprise and consumer computer systems. The performance characteristics of these new devices have prompted a considerable amount of research that aims at developing efficient data access methods. Early works attempted to reduce the expensive random writes, exploiting logging and batch write techniques, while more recent ones addressed query processing, taking advantage of the high internal parallelism of SSDs. 3D XPoint is a new nonvolatile memory technology that has emerged recently, featuring smaller access times and higher durability compared with flash. It is available both as block addressable secondary storage and as byte addressable persistent main memory. However, the high cost of 3D XPoint prevents, for the moment, its adoption in large scales. This renders hybrid storage systems utilizing NAND flash and 3D XPoint a sufficient alternative. In this work, we propose HyR-tree, a hybrid variant of R-tree that persists a part of the tree in the high performing 3D XPoint storage. HyR-tree identifies repeated access pattern to the data and uses these patterns to locate the most important nodes. The importance of a node is determined by the performance gain that derives from its placement within a 3D XPoint-based device. We experimentally evaluated HyR-tree using real devices and four different datasets. The acquired results show that our proposal achieves significant performance gains up to 40% in tree construction and up to 56% in range queries. [ABSTRACT FROM AUTHOR]

Abstract: In most forested environments, boreal forest in particular, monitoring and evaluation of management activities would be facilitated by storage of multiscale data sets spanning long time periods. For this study, such a data repository based on a generic spatio-temporal conceptual data model was created using XML. The data repository containing changes in data content for a 1000ha forest estate between 1871 and 1994 was used to evaluate the data retrieval capabilities of XQuery. The data retrieval operations consisted of pivoting, sequencing, and aggregation. Pivoting transforms the generic attribute storage used in the data model into a more compact column-wise format. Sequencing is used to return a temporal sequence of values, and for the traversal of the object hierarchy. Aggregation aggregates the values of a variable over a grouping variable. The combinations of the basic retrieval operations were also investigated as well as the effect of time and object hierarchy on the retrieval operations. The conceptual match between the generic spatio-temporal data model and the XML data model was apparent at the data retrieval operations. The key properties of XQuery for the implementation of the retrieval operations were extendability, support for nested structures, and data transformation functionality. [Copyright &y& Elsevier]