3413469
The computational requirements of mobile machines
For the last few years mobile (or nomadic) computing has generated tremendous interest in both the research and the industrial community. Mobility is seen as an area of great potential benefits, both in terms of products and research contributions, However, at this time, mobile systems are so novel that there is little practical experience regarding their use. This has led to much speculation regarding a number of system issues such as determining what the killer apps will be, the hardware architecture of the nomadic machines, deciding whether communication or computation will be their primary feature and so on. One of the issues yet to be resolved is that of the architecture of these machines. Will mobile machines be essentially a new type of portable computer (although perhaps smaller, less powerful, friendlier, and pencentric) or will we carry around with us the equivalent of an X-window terminal (i.e., simply a display device, with all computation being carried out at a non-mobile server)? Examples of the first approach are the Apple Newton and the EO computers formerly marketed by AT&T, while the second approach is being explored by a number of other researchers (e.g., the InfoPad project at U.C. Berkeley, or the Xerox PARC tabs). This paper briefly describes the research issues involved and outlines the pros and cons of either approach. We also explore in detail one particular aspect, namely, the performance implications of the choice of architecture in a distributed information system. The results are presented as a set of simulation-based studies.
59895916
Concurrency Control and Recovery for Global Procedures in Federated Database Systems
5881433
An advisor for flexible working sets
The traditional model of virtual memory working sets does not account for programs that can adjust their working sets on demand. Examples of such programs are garbage-collected systems and databases with block cache buffers. We present a memory-use model of such systems, and propose a method that may be used by virtual memory managers to advise programs on how to adjust their working sets. Our method tries to minimize memory contention and ensure better overall system response time. We have implemented a memory “advice server” that runs as a non-privileged process under Berkeley Unix. User processes may ask this server for advice about working set sizes, so as to take maximum advantage of memory resources. Our implementation is quite simple, and has negligible overhead, and experimental results show that it results in sizable performance improvements.
29614860
A mobile computer interface for heterogeneous databases
Computer-based personal information services are evolving beyond simple applications such as retrieval of phone numbers to include interaction with collections of large, heterogeneous, geographically distributed information bases. Concurrently, small, pen-based, mobile computers are becoming the machine of choice for personal computing. This latter trend suggests simple interfaces that are easy-to-use, avoid keyboard use, and are suited for the small screens and small memory sizes of mobile machines. The former trend, however, suggests an increased sophistication in database interfaces, so as to provide access to the more complex heterogeneous collection of databases that are now part of a personal information service. At the Matsushita Information Technology Laboratory (MITL) they are working on a pen-based graphical database language that begins to combine these conflicting demands for simplicity and sophistication. The authors sketch the highlights of the research approach, and present a brief description of the current prototype.<<ETX>>
41657422
Long-Term Caching Strategies for Very Large Distributed File Systems
52874049
Negotiating data access in federated database systems
A protocol is presented for negotiating access to data in a federated database. This protocol deals with several important aspects of data sharing in an environment where databases belonging to different organizations coexist and cooperate. It is based on the concept of quasicopies. These are cached values that are allowed to deviate from the central value in a controlled fashion. The degree of consistency of a quasicopy is established by the entity where the quasicopy is to reside. Two techniques are presented that can be used for numerical data and for copies that rely on version numbers. It is believed that these two ideas encompass many of the interesting cases in practice. However, it is also possible to fine tune the estimation of this function once the exact semantics of the data involved are known.<<ETX>>
29591299
Trade Press News
42014672
Trade Press News - Announcement and Preface