File Requests Research Articles

Order From Chaos

B ENOIT is a fractal analysis software product for Windows 95, Windows 98, or Windows NT used to find order and patterns in seemingly chaotic data, particularly where traditional statistical approaches to data analysis fail. It is widely used in disciplines as diverse as biology, chemistry, physics, economics, medicine, and geology. The U.S. Geological Survey, for example, employs fractal analysis to accurately predict the volume of undiscovered deposits of oil and natural gas, on the basis of data from known deposits. BENOIT measures user-supplied data by standard fractal methods. For a fractal, measures change in value as the scale decreases in size because ever-smaller pieces become included in the analysis. Measures are plotted as a function of ruler size on a log-log plot, and a fractal dimension is calculated from the slope of the resulting line. Users select one of 10 analytical measures with the software. Five of the available measures in the program act upon bitmap images in Windows BMP format. These are described as the “self-similar” or two-dimensional (2D) methods, while the remaining group of routines act upon time-series or 1D data. The latter group requires data to be in a simple but specific data format, such as is available in Excel. The program also features a data generator that produces files with a given fractal dimension. Users may find this useful for testing and control purposes. The self-similar or image methods available in BENOIT measure different characteristics of bitmap objects in ways that should be scale-invariant. A real dataset normally has some fractal limit, and outside the limit, the fractal dimension will return a trivial value (1 for time-series or 2 for image data). Upper and lower fractal limits are controlled by the size of the dataset. Self-similar methods available in BENOIT are well known in fractal analysis: box dimension, perimeter-area dimension, information dimension, and ruler dimension. All methods are explained in standard Help files that contain several pages of information for each topic. The 1D analysis routines use “self-affine” methods of analysis. Self-affine fractals differ from self-similiar fractals in that their parts need to be rescaled by different factors in different coordinates to resemble the original. In the roughness-length method, the root-mean-square variation or roughness of the data is calculated for a variety of horizontal scales. The operation provides an estimate of the Hurst exponent, H , in a log-log plot, which is related to the fractal dimension. Standard self-affine methods available include R/S (Rescaled Range) analysis, power spectrum, roughness-length, variogram, and wavelets. Printing of log-log figures is provided, but without many features that would be found in a spreadsheet. Documentation for the program is available online. BENOIT has a highly visual interface, complete with an animated grid or ruler for self-similar fractal methods, and it gives users control of all calculations that the program performs, unlike other fractal software. Benoit is not without flaws. Some operations, such as name registration with the Windows NT 4.0 taskbar and the Open File requester, do not conform to standard Windows conventions. It would be of help to have an outline or flowchart of the operation of the different routines available in BENOIT for newcomers to fractal analysis. In summary, the variety of fractal analysis methods available in BENOIT, together with generally detailed help files and significant user control of operations, make BENOIT a good resource for learning about and using fractal analysis methods.

Exp1: a comparison between a simple adaptive caching agent using document life histories and existing cache techniques

Hierarchical storage of Web pages in proxy server and client browser caches introduce coherence problems, which require cache management techniques which are both accurate and computationally efficient. We suggest that current approaches, such as the most common Least Recently Used (LRU) technique, are inadequate for future network loads as they do not incorporate the dynamics of document selection and modification. We propose the use of an intelligent, adaptive cache management technique to overcome the coherence problem by using document life histories to optimise cache performance. This work addresses the use of damped exponential smoothing to model accurately the frequency of file requests and modifications, in order to predict the future value of cached files. Finally, we make a mathematical analysis of LRU in comparison with our technique, showing how and why the use of document life histories is a more effective cache management technique without imposing major computational overheads.

WebMonitor: a Tool for Measuring World-Wide Web Server Performance

Server performance has become a crucial issue for improving the overall performance of the World-Wide Web. This paper describes WebMonitor, a tool for evaluating and understanding server performance, and presents new results for realistic workloads. WebMonitor measures activity and resource consumption, both within the kernel and in HTTP processes running in user space. WebMonitor is implemented using an efficient combination of sampling and event-driven techniques that exhibit low overhead. Our initial implementation is for the Apache World-Wide Web server running on the Linux operating system. We demonstrate the utility of WebMonitor by measuring and understanding the performance of a Pentium-based PC acting as a dedicated WWW server. Our workloads use file size distributions with a heavy tail. This captures the fact that Web servers must concurrently handle some requests for large audio and video files, and a large number of requests for small documents, containing text or images. Our results show that in a Web server saturated by client requests, up to 90% of the time spent handling HTTP requests is spent in the kernel. These results emphasize the important role of operating system implementation in determining Web server performance. It also suggests the need for new operating system implementations that are designed to perform well when running on Web servers.

File migration and file replication: a symbiotic relationship

Much of the past research on file migration and file replication has examined these two resource management strategies in isolation or in an environment where they do not work together. We establish through simulation that these two strategies can be utilized simultaneously to potentially provide significant performance benefits over a system without file migration or replication. File replication can be viewed as a natural extension to file migration, and thus, we derive a dynamic file replication policy based on an established file migration heuristic: a file is migrated (or replicated) whenever a reduction in total mean response time of the file requests currently in the affected storage sites can be achieved. Through our performance model, we use simulation to establish the conditions under which our file migration/replication policies are beneficial in a distributed file system.

Prestiż zawodu sędziego i społeczny wizerunek instytucji wymiaru sprawiedliwości

Prestiż zawodu sędziego i społeczny wizerunek instytucji wymiaru sprawiedliwości

A Video Server cost/performance Estimator tool

The Video Server Estimator (VSE) is an analytical tool which allows a user to perform a cost/performance analysis of video servers with hierarchical storage. The underlying model comprises multiple systems, main memory, expanded storage, disks and a tape library. The main objective of the tool is to optimally allocate the video files to different storage media based on the system parameters and the video file request probability distribution. The cost and the size of the video server that can accommodate a customer profile are determined. Furthermore, the impact of design parameters on the cost and performance are examined through a parametric analysis.

A numerically intensive computing environment: IBM 3090 and the PS/2 Model 80

Recent advances in personal computer workstations, such as the IBM Personal System/2® Model 80 with its increased memory and CPU speed, loosely coupled with a host IBM 3090™ Processor, can provide considerable computing advantages for executing and visualizing numerically intensive computing (NIC) applications. We have developed a prototype visualization environment which demonstrates effective use of this hardware. The user interface for the NIC application is written using Microsoft Windows® on the PS/2® Model 80 running DOS 3.3. The PS/2 Model 80 is connected to a host 3090 via a PC network. The user enters requests which are application parameters and selects graphic views for displaying the output results file. The entries are made through user dialog screens on the workstations. The user view of the system is such that it appears that it is running on the workstation. To achieve this transparency, caches are used on both the workstation and the host. The cache on the host is in the form of graphic metafiles and numeric data. The cache on the workstation contains metafiles. Requests are monitored on the workstation to determine whether the results are in the local cache. When they are not, a request file is transferred to the host and checked against the host cache. The NIC application is run only when the requested result is not in either cache. In order to reduce the file size, the results file is converted to a metafile before being transferred to the workstation.

Stability, availability, and response in network file service

A network file system called Multifile is described. It meets response, availability, and stability requirements as primitive functions. Multifile has a high degree of responsiveness because its component parts compete among themselves to service file requests; it has high availability because it maintains multiple copies of files; and it exhibits stable behavior over wise range of system parameters. The responsiveness of Multifile to read requests improves as the number of pages per request rises, implying that read ahead pages can profitably be cached at client sites. The throughput of Multifile improves as the request size increases and as the number of clients increases. As server load increases, the responsiveness of Multifile to read requests is stable in most configurations. The throughput of writes is unstable as the number of pages in the wire request rises, implying that write back pages should not be cached at client sites. The scale of events in file service is dominated by disk activity, so lost message exceptions do not occur frequently enough to affect file service; however, duplicate message exceptions are a factor in performance. >

FREEDOM OF INFORMATION IN AUSTRALIA, CANADA AND NEW ZEALAND

In 1982, Australia, Canada and New Zealand introduced freedom of information (FOI) laws. The author visited all three countries in 1986‐7 to study how the legislation was being used, and its impact on the workings of Westminster‐style government. A table summarizes the main features of the legislation. The article discusses the different appeal mechanisms; the implications for ministerial accountability; the level of take‐up; the different categories of user; administrative costs and benefits; staffing requirements, refusal rates, fees, etc. Apart from requests for personal files, the level of demand has been relatively low; ministerial accountability remains unchanged; the legislation has successfully protected government secrets; and the overall cost has not proved too great. FOI has not realized its more ambitious objectives, such as increasing public participation in government decision‐making; but at the same time, it has not fulfilled many of its opponents' worst fears.

Organizing the annual housing surveys as a very large relationally oriented data base

Since 1973, the Department of Housing and Urban Development, through the Bureau of the Census, has conducted a yearly nationwide survey of housing. Data on a wide range of topics are collected during face to face interviews with over 190,000 individuals. Plainly, the Annual Housing Surveys represent one of the largest longitudinal general social and economic data collection efforts ever undertaken.Due to changing policy and substantive interests, as well as government requirements, the interview schedules have changed significantly from year to year. Since the great potential for data from the Annual Housing Survey is in longitudinal analysis, it is necessary to have common variable definitions and consistent formats.To accomplish this, we have developed and implemented a system which includes: 1) documentation of the variables, questionnaires, and files across all years and surveys; 2) files created using one homogeneously defined data structure; 3) a simple system to produce custom user files; 4) a method to easily produce routine custom analyses and tabulations using the data.We have applied the relational model to create a small data base which documents the interview schedules, files and variable definitions. From this we produce up to date documentation and computer programs which are used to update the Annual Housing Survey data base, to handle custom file requests, and to perform analyses.

A Queueing Model of Multiprogrammed Computer Systems Under Full Load Conditions

This paper presents a queueing model of a multiprogrammed computer system with virtual memory. Two system organizations are considered: (i) all the processes present in the system share primary storage; (ii) processes which have generated a file request (slow I/O) lose their memory space until the I/O is completed. Our model assumes balanced memory allocation among processes, and accounts for the memory sharing effect through the use of lifetime functions. The model explicitly takes into account the fact that, if a written-onto page is to be replaced at the moment of a page fault, it first has to be saved in the secondary memory. An approximate closed form solution is obtained by using an equivalence and decomposition approach. A procedure for evaluating the accuracy of the approximation is presented. The numerical examples illustrate the influence of the system and program behavior parameters taken into account in our model.

Dynamic file assignment in a computer network

We present the models describing a problem of dynamic file allocation in a network of interacting computers and use dynamic programming to solve for the optimal strategies. The problem is treated for the case when the rates of the file requests are known in advance, as well as when only prior statistics is available for these rates. A separation theorem between estimation of the rates and the optimal control is proven, similar to Wonham's separation theorem for linear Gaussian models.

A model of a virtual memory system

We present a queueing network model of a virtual memory computer system including the effect of memory sharing among processes. Page fault and file request system overheads are explicitly taken into account. The fact that some memory pages have to be saved in the secondary memory at the moment of a page fault, is also taken into consideration. We obtain an approximate solution using an equivalence and decomposition approach. The effect of system and program behavior parameters (primary memory size, drum and disk characteristics, program locality, input-output rates and different pages ratios) as well as that of the total number of processes, are examined for two different system organizations. In the first one, all the processes share real core; in the second, processes having issued a file request lose their memory space until the I/O is performed.