Managing database server performance to meet QoS requirements in electronic commerce systems

The performance of electronic commerce systems has a major impact on their acceptability to users. Different users also demand different levels of performance from the system, that is, they will have different Quality of Service (QoS) requirements. Electronic commerce systems are the integration of several different types of servers and each server must contribute to meeting the QoS demands of the users. In this paper we focus on the role, and the performance, of a database server within an electronic commerce system. We examine the characteristics of the workload placed on a database server by an electronic commerce system and suggest a range of QoS requirements for the database server based on this analysis of the workload. We argue that a database server must be able to dynamically reallocate its resources in order to meet the QoS requirements of different transactions as the workload changes. We describe Quartermaster, which is a system to support dynamic goal-oriented resource management in database management systems, and discuss how it can be used to help meet the QoS requirements of the electronic commerce database server. We provide an example of the use of Quartermaster that illustrates how the dynamic reallocation of memory resources can be used to meet the QoS requirements of a set of transactions similar to transactions found in an electronic commerce workload. We briefly describe the memory reallocation algorithms used by Quartermaster and present experiments to show the impact of the reallocations on the performance of the transactions. Published online: 22 August 2001     

Cost-based tolerancing of optical systems

When designing an optical system it is generally accepted that it is too costly to generate the entire Hessian for every iteration of an optimizer. However, the Hessian also is useful in tolerance analysis for which it needs to be calculated only once. We propose using the Hessian as part of a cost-based tolerancing procedure. Considerations for the general implementation of the proposed ideas are discussed, and the utility of this approach is demonstrated by way of an example. In the example optimal manufacturing tolerances are determined for a doublet. As expected, the optimal tolerances change as quantities such as the requisite image quality for finished systems, manufacturing yields, and relative expenses of meeting given tolerances are varied.     

Imaging with three spherical mirrors

Unobstructed, plane-symmetric systems of three spherical mirrors are investigated. Twelve parameters are necessary to specify the configuration of such a system. Constraints are determined to eliminate four of these parameters as independent degrees of freedom. These constraints ensure appropriate first-order behavior and are used to aid in two example design studies-one for a class of systems with the object at infinity and another for a class of finite conjugate projection systems. For the first study, a portion of the associated merit-function space is systematically evaluated and plotted, and the results are compared with those obtained when a global optimizer is used. For the second study, a global optimizer is employed as the primary search tool. Example systems from both studies are presented.     

Absolute interferometry with a 670-nm external cavity diode laser

In the past few years there has been much interest in use of tunable diode lasers for absolute interferometry. Here we report on use of an external cavity diode laser operating in the visible (lambda ~ 670 nm) for absolute distance measurements. Under laboratory conditions we achieve better than 1-mum standard uncertainty in distance measurements over a range of 5 m, but significantly larger uncertainties will probably be more typical of shop-floor measurements where conditions are far from ideal. We analyze the primary sources of uncertainty limiting the performance of wavelength-sweeping methods for absolute interferometry, and we discuss how errors can be minimized. Many errors are greatly magnified when the wavelength sweeping technique is used; sources of error that are normally relevant only at the nanometer level when standard interferometric techniques are used may be significant here for measurements at the micrometer level.     

Using informal notes for sharing corporate technology know-how

Corporate and academic communities have focused a great deal of attention on formalized approaches for creating, capturing, and propagating knowledge. Far less attention has been paid to the informal mechanisms that individuals share and employ to help them navigate complex processes in order to ‘get things done.’ In this paper, we examine the creation, use, and content of informal documents for supporting users of an enterprise resource planning system in a Fortune 500 company. We contend that such notes, which are commonly used for supporting information systems-related work, are an overlooked source of knowledgeability about organizational practices. This study is a first but necessary step in analyzing the types of information that can be derived from informal notes so that organizations can more fully utilize this largely untapped resource.     

A Framework for Average Case Analysis of Conjunctive Learning Algorithms

We present an approach to modeling the average case behavior of learning algorithms. Our motivation is to predict the expected accuracy of learning algorithms as a function of the number of training examples. We apply this framework to a purely empirical learning algorithm, (the one-sided algorithm for pure conjunctive concepts), and to an algorithm that combines empirical and explanation-based learning. The model is used to gain insight into the behavior of these algorithms on a series of problems. Finally, we evaluate how well the average case model performs when the training examples violate the assumptions of the model.     

Storage in the power PC

Power PC memory is innovative because it incorporates leading-edge approaches to hiding the latency of memory accesses. Although features like access reordering have long been the subject of academic research, such improvements are only now coming into widespread commercial use. Using these features requires a shift in thinking, but designers and programmers can achieve significant performance advantages. We also compare the Power PC memory to the DEC Alpha and Mips R4000 storage architectures     

Delayed development of symptomatic improvement by (--)-deprenyl in Parkinson's disease

Twenty de novo patients with Parkinson's disease (Hoehn-Yahr stages I, II, III) were studied in a double blind trial after introducing (--)-deprenyl monotherapy. The parkinsonian symptoms were assessed by a novel graded clinical rating scale, by UPDRS and by the North Western self-rating scale. A significant change was observed in motor behaviour and daily activity (UPDRS) after 3 weeks of treatment with (--)-deprenyl at 10 mg/day. The total scores using UPDRS and the North Western ratings were changed significantly after 4 weeks. The greatest changes observed were in walking and in hypokinesia. Rigidity was not modified by (--)-deprenyl.