11125586
The Behavior of Database Concurrency Control Mechanisms under Bursty Arrivals
The robustness and sensitivity of four two-phase databases concurrency control mechanisms are studied under a dynamically changing workload due to the bursty arrival of transactions. The concurrency control mechanisms are studied under closely controlled conditions in which the only variable is the coefficient of variance of the arrival rate distribution. This paper shows that bursty traffic does impact the performance of the concurrency control mechanisms at both high and low loads, and that the degree of this impact is different for the different mechanisms investigated. We also show that the behavior of some CCMs change significantly under such environment.
18344625
Concurrent operations on extendible hashing and its performance
Extendible hashing is a dynamic data structure which accommodates expansion and contraction of any stored data efficiently. In this article, an algorithm has been developed for managing concurrent operations on extendible hashing by achieving optimal memory utilization by supporting directly expansion and contraction, page split, and merge. The results of this study have been encouraging in the sense that it seems to provide a higher degree of concurrency compared to other algorithms on an extendible hash file.
16958826
Recent Advances and Research Problems in Data Warehousing
In the recent years, the database community has witnessed the emergence of a new technology, namely data warehousing. A data warehouse is a global repository that stores pre-processed queries on data which resides in multiple, possibly heterogeneous, operational or legacy sources. The information stored in the data warehouse can be easily and efficiently accessed for making effective decisions. The On-Line Analytical Processing (OLAP) tools access data from the data warehouse for complex data analysis, such as multidimensional data analysis, and decision support activities. Current research has lead to new developments in all aspects of data warehousing, however, there are still a number of problems that need to be solved for making data warehousing effective. In this paper, we discuss recent developments in data warehouse modelling, view maintenance, and parallel query processing. A number of technical issues for exploratory research are presented and possible solutions are discussed.
39362526
Main memory database recovery algorithms and their performance
In main memory systems recovery becomes more complex mainly due to the volatility of main memory and the elimination of the separation of data storage (disk) and data processing locations (main memory). In a disk based database system, it is the disk copy that represents the stable database restored after a system failure; but in MDBSs, the main memory copy of the database must be recovered. The paper discusses the recovery issues in MDBSs and presents a somewhat detailed performance study of two recovery algorithms, one using a shadow approach and the other update-in-place.<<ETX>>
8261257
TCOT-A Timeout-Based Mobile Transaction Commitment Protocol
We present a transaction commit protocol, "Transaction Commit On Timeout (TCOT)," based on a "timeout" approach for Mobile Database Systems (MDS), which can be universally used to reach a final transaction termination decision (e.g., commit, abort, etc.) in any message-oriented system. Particularly suited for a wireless environment, a timeout mechanism is the only way to minimize the impact of the slow and unreliable wireless link. We compare TCOT to a modified version of 2PC to show its superiority based on commit time.
29393244
Semantic Caching and Query Processing
Semantic caching is very attractive for use in distributed systems due to the reduced network traffic and the improved response time. It is particularly efficient for a mobile computing environment, where the bandwidth of wireless links is a major performance bottleneck. Previous work either does not provide a formal semantic caching model, or lacks efficient query processing strategies. This paper extends the existing research in three ways: formal definitions associated with semantic caching are presented, query processing strategies are investigated and, finally, the performance of the semantic cache model is examined through a detailed simulation study.
18117520
Control and Coordination of Multiple Mobile Robots in Manipulation and Material Handling Tasks
We describe a framework and control algorithms for coordinating multiple mobile robots with manipulators focusing on tasks that require grasping, manipulation, and transporting large and possibly flexible objects without special purpose fixtures. Because each robot has an independent controller and is autonomous, the coordination and synergy are realized through sensing and communication. The robots can cooperatively transport objects and march in a tightly controlled formation, while also having the capability to navigate autonomously. We describe the key aspects of the overall hierarchy and the basic algorithms, with specific applications to our experimental testbed consisting of three robots.
1926044
Real-time vision-based control of a nonholonomic mobile robot
This paper considers the problem of vision-based control of a nonholonomic mobile robot. We describe the design and implementation of real-time estimation and control algorithms on a car-like robot platform using a single omni-directional camera as a sensor without explicit use of odometry. We provide experimental results for each of these vision-based control objects. The algorithms are packaged as control modes and can be combined hierarchically to perform higher level tasks involving multiple robots.
1752850
High Performance Data Mining
Recent times have seen an explosive growth in the availability of various kinds of data. It has resulted in an unprecedented opportunity to develop automated data-driven techniques of extracting useful knowledge. Data mining, an important step in this process of knowledge discovery, consists of methods that discover interesting, non-trivial, and useful patterns hidden in the data [SAD+93, CHY96]. The field of data mining builds upon the ideas from diverse fields such as machine learning, pattern recognition, statistics, database systems, and data visualization. But, techniques developed in these traditional disciplines are often unsuitable due to some unique characteristics of today's data-sets, such as their enormous sizes, high-dimensionality, and heterogeneity. There is a necessity to develop effective parallel algorithms for various data mining techniques. However, designing such algorithms is challenging, and the main focus of the paper is a description of the parallel formulations of two important data mining algorithms: discovery of association rules, and induction of decision trees for classification. We also briefly discuss an application of data mining to the analysis of large data sets collected by Earth observing satellites that need to be processed to better understand global scale changes in biosphere processes and patterns.
5622554
Equilibria in topology control games for ad hoc networks
We study topology control problems in ad hoc networks, where network nodes get to choose their power levels in order to ensure desired connectivity properties. Unlike most other work on this topic, we assume that the network nodes are owned by different entities, whose only goal is to maximize their own utility that they get out of the network without considering the overall performance of the network. Game theory is the appropriate tool to study such selfish nodes: we define several topology control games in which the nodes need to choose power levels in order to connect to other nodes in the network to reach their communication partners while at the same time minimizing their costs. We study Nash equilibria and show that -- among the games we define -- these can only be guaranteed to exist if all network nodes are required to be connected to all other nodes (we call this the Strong Connectivity Game). We give asymptotically tight bounds for the worst case quality of a Nash equilibrium in the Strong Connectivity Game and we improve these bounds for randomly distributed nodes. We then study the computational complexity of finding Nash equilibria and show that a polynomial-time algorithm finds Nash equilibria whose costs are at most a factor 2 off the minimum cost possible; for a variation called Connectivity Game, where each node is only required to be connected (possibly via intermediate nodes) to a given set of nodes, we show that answering the question, if a Nash equilibrium exists, is NP-hard, if the network graph satisfies the triangle inequality. For a second game called Reachability Game, where each node tries to reach as many other nodes as possible, while minimizing its radius, we show that 1+o(1)-approximate Nash equilibria exist for randomly distributed nodes. Our work is a first step towards game-theoretic analyses of ad hoc networks.
6412662
Abstraction and control for groups of fully-actuated planar robots
This paper shows how a large number of robots can be coordinated by designing control laws on a small dimensional manifold, independent on the number and ordering of the robots. The small dimensional description of the team has a product structure of a Lie group, which captures the dependence of the ensemble on world frame, and a shape manifold, which is an intrinsic description of the team. We design decoupled controls for group and shape. The individual control laws which are mapped to the desired collective behavior can be realized by feedback depending only on the current state of the robot and the state on the small dimensional manifold, so that the robots have to broadcast their states and only have to listen to some coordinating agent with small bandwidth.