GPUs are being applied widely to batch workloads that benefit from the parallel processing capabilities of GPUs. To enable the processing of concurrent batch-based transactions on GPUs, existing systems build dependency graphs during a pre-execution phase to manage read and write operations. However, as dependency-graph maintenance introduces a sub-stantial overhead, there is a need for more efficient transaction support to exploit the power of GPUs more fully for transaction processing. This paper proposes LTPG, a novel GPU-enabled database system that offers increased versatility and efficiency by eliminating the need for predefined read/write-sets. LTPG employs deterministic optimistic concurrency control to ensure correct transaction execution, thus avoiding the maintenance of dependency graphs. The proposed concurrency control simpli-fies transaction processing workflows and avoids the overhead associated with managing dependency graphs, thus resulting in improved efficiency. LTPG divides a workflow into three stages: execution, conflict detection, and write-back, leveraging the parallelism of GPUs. Moreover, several additional optimization strategies are adopted to improve system performance. Experiments with real-world workloads from two benchmarks verify LTPG can achieve effective improvement in the throughput and latency compared to the leading baselines.

Skyline computation is an essential database operation that has many applications in multi-criteria decision making scenarios such as recommender systems. Existing algorithms have focused on checking point domination, which lack efficiency over large datasets. We propose a grid-based structure that enables grid cell domination checks. We show that only a small constant number of cells need to be checked which is independent from the number of data points. Our structure also enables parallel processing. We thus obtain a highly efficient parallel skyline algorithm named SkyCell, taking advantage of the parallelization power of graphics processing units. Experimental results confirm the effectiveness and efficiency of SkyCell -- it outperforms state-of-the-art algorithms consistently and by up to over two orders of magnitude in the computation time.

Abstract Hyperspace hashing which is often applied to NoSQL data-bases builds indexes by mapping objects with multiple attributes to a multidimensional space. It can accelerate processing queries of some secondary attributes in addition to just primary keys. In recent years, the rich computing resources of GPU provide opportunities for implementing high-performance HyperSpace Hash. In this study, we construct a fully concurrent dynamic hyperspace hash table for GPU. By using atomic operations instead of locking, we make our approach highly parallel and lock-free. We propose a special concurrency control strategy that ensures wait-free read operations. Our data structure is designed considering GPU specific hardware characteristics. We also propose a warp-level pre-combinations data sharing strategy to obtain high parallel acceleration. Experiments on an Nvidia RTX2080Ti GPU suggest that GHSH performs about 20-100X faster than its counterpart on CPU. Specifically, GHSH performs updates with up to 396 M updates/s and processes search queries with up to 995 M queries/s. Compared to other GPU hashes that cannot conduct queries on non-key attributes, GHSH demonstrates comparable building and retrieval performance.

The k nearest neighbor (kNN) query in road networks is a traditional query type in spatial databases. This query has found new applications in the fast-growing location-based services, e.g., finding the k nearest Uber cars of a user for ridesharing. KNN queries in these applications are non-trivial to process due to the frequent location updates of data objects (e.g., movements of the cars). This calls for novel spatial indexes with high efficiency in not only query processing but also update handling. To address this need, we propose an index structure that uses a "lazy update" strategy to reduce the costs of update handling without sacrificing query efficiency or answer accuracy. We cache the location updates of data objects and only update the corresponding entries in the index when they are queried. We further propose a kNN query algorithm based on this index. This algorithm takes advantage of the strengths of both the CPU and the GPU. It first identifies the queried region and updates the index over this region using the GPU. Then, it uses the GPU to query the index and produce a candidate result set, which is later refined by the CPU to obtain the final query answer. We conduct experiments on real data and compare the proposed algorithm with state-of-the-art kNN algorithms. The experimental results show that the proposed algorithm outperforms the baseline algorithms by orders of magnitude in query time.

We revisit the moving k nearest neighbor (MkNN) query, which computes one's k nearest neighbor set and maintains it while at move. Existing MkNN algorithms are mostly safe region based, which lack efficiency due to either computing small safe regions with a high recomputation frequency or computing larger safe regions but with a high cost for each computation. In this demonstration, we showcase a system named INSQ that adopts a novel algorithm called the Influential Neighbor Set (INS) algorithm to process the MkNN query in both two-dimensional Euclidean space and road networks. This algorithm uses a small set of safe guarding objects instead of safe regions. As long as the the current k nearest neighbors are closer to the query object than the safe guarding objects are, the current k nearest neighbors stay valid and no recomputation is required. Meanwhile, the region defined by the safe guarding objects is the largest possible safe region. This means that the recomputation frequency is also minimized and hence, the INS algorithm achieves high overall query processing efficiency.

The moving k nearest neighbor query, which computes one's k nearest neighbor set and maintains it while at move, is gaining importance due to the prevalent use of smart mobile devices such as smart phones. Safe region is a popular technique in processing the moving k nearest neighbor query. It is a region where the movement of the query object does not cause the current k nearest neighbor set to change. Processing a moving k nearest neighbor query is a continuing process of checking the validity of the safe region and recomputing it if invalidated. The size of the safe region largely decides the frequency of safe region recomputation and hence query processing efficiency. Existing moving k nearest neighbor algorithms lack efficiency due to either computing small safe regions and have to recompute frequently or computing large safe regions (i.e., an order- k Voronoi cell) with a high cost. In this paper, we take a third approach. Instead of safe regions, we use a small set of safe guarding objects. We prove that, as long as the the current k nearest neighbors are closer to the query object than the safe guarding objects, the current k nearest neighbors stay valid and no recomputation is required. This way, we avoid the high cost of safe region recomputation. We also prove that, the region defined by the safe guarding objects is the largest possible safe region. This means that the recomputation frequency of our method is also minimized. We conduct extensive experiments comparing our method with the state-of-the-art method on both real and synthetic data sets. The results confirm the superiority of our method.

In recent years, there has been a growing need for location-based services (LBS), ranging from resource tracking to personal life assistance. The Moving k Nearest Neighbor (MkNN) query is a main problem in the LBS area, which retrieves the top k nearest neighbors while the query consumer moves. Considerable attention is attracted to this query type and a large number of studies are proposed recently. Most of these studies focus on ideal Euclidean plane where any two points are visible. In this paper, we propose a method to process MkNN queries in areas with obstacles, which is more realistic. We propose the obstacle-free safe region (OSR) concept within which a query point has the same kNN. No additional processing is required when the query consumer moves inside one OSR. Several novel properties are also introduced and employed in our efficient MkNN processing algorithm. Our experimental results show that our approach handles the MkNN queries with high accuracy and works efficiently.

Cyber-Physical Systems (CPS) are integrations of computation with physical processes, and applications of CPS will appear in a wide variety of fields. As part of CPS, sensor networks can observe a physical system by acquiring data and processing queries. In this paper, a query processing approach based on a queuing model is proposed for a mass of periodic queries and ad hoc queries, which are both expected to be supported simultaneously for the soft real-time applications in the large-scale sensor networks. A query processing region is provided as a buffer where the nodes are able to map the data of remote nodes and queries, so as to process queries in time. Based on queuing theory, a management model is developed for the queries in the buffer with its optimization scheme designed, thus giving the appropriate width and position of the buffer to design the algorithm of query processing. The experimental results show that this approach is very efficient at decreasing the query misses and saving the energy.