Abstract not found

A semantic file system is an information storage system that provides flexible associative access to the system's contents by automatically extracting attributes from files with file type specific transducers. Associative access is provided by a conservative extension to existing tree-structured file system protocols, and by protocols that are designed specifically for content based access. Compatibility with existing file system protocols is provided by introducing the concept of a virtual directory. Virtual directory names are interpreted as queries, and thus provide flexible associative access to files and directories in a manner compatible with existing software. Rapid attribute-based access to file system contents is implemented by automatic extraction and indexing of key properties of file system objects. The automatic indexing of files and directories is called "semantic" because user programmable transducers use information about the semantics of updated file system objects to extract the properties for indexing. Experimental results from a semantic file system implementation support the thesis that semantic file systems present a more effective storage abstraction than do traditional tree structured file systems for information sharing and command level programming.

Plan 9 is a distributed computing environment. It is assembled from separate machines acting as CPU servers, file servers, and terminals. The pieces are connected by a single file-oriented protocol and local name space operations. By building the system from distinct, specialised components rather than from similar general-purpose components, Plan 9 achieves levels of efficiency, security, simplicity, and reliability seldom realised in other distributed systems. This paper discusses the building blocks, interconnections, and conventions of Plan 9. Introduction. Plan 9 is a general-purpose, multi-user, portable distributed system implemented on a variety of computers and networks. It lacks a number of features often found in other distributed systems, including (i) A uniform distributed name space, (ii) Process migration,

The rapid increase in performance of mass market commodity microprocessors and significant disparity in pricing between PCs and scientific workstations has provided an opportunity for substantial gains in performance to cost by harnessing PC technology in parallel ensembles to provide high end capability for scientific and engineering applications. The Beowulf project is a NASA initiative sponsored by the HPCC program to explore the potential of Pileof -PCs and to develop the necessary methodologies to apply these low cost system configurations to NASA computational requirements in the Earth and space sciences. Recently, a 16 processor Beowulf costing less than $50,000 sustained 1.25 Gigaflops on a gravitational Nbody simulation of 10 million particles with a Tree code algorithm using standard commodity hardware and software components. This paper describes the technologies and methodologies employed to achieve this breakthrough. Both opportunities afforded by this approach and the cha...

(to appear in Software-Practice and Experience) A signi cant amount of software development isevolutionary, involving the modi cation of already existing programs. To a large extent, the modi ed programs produce the same results as the original program. This similarity between the original program and the development program is utilized by relative debugging. Relative debugging is a new concept that enables the user to compare the execution of two programs by specifying the expected correspondences between their states. A relative debugger concurrently executes the programs, veri es the correspondences, and reports any di erences found. We describe our novel debugger, called Guard, and its relative debugging capabilities. Guard is implemented by using our library of debugging routines, called Dynascope, which provides debugging primitives in heterogeneous networked environments. To demonstrate the capacity of Guard for debugging in heterogeneous environments, we describe an experiment in which the execution of two programs is compared across Internet. The programs are written in di erent programming languages and executing on di erent computing platforms.

This paper presents a library of directing commands which enable the construction of powerful directors. The interface has been implemented in a Unix environment as a runtime subsystem running in the directed program's address space. The paper provides the description of the interface and the basic programming techniques in building directors. Examples of novel applications, illustrating the use of the directing interface, are demonstrated by the directors for the visualization of program control and structured snapshots

The combined force behind ubiquitous mobile computing and storage devices and universal network access has created a unique era of mobile network computing, in which computation units ranging from a single process to an entire host can move while communicating with each other across the network. A key problem therefore is how to preserve the ongoing network communication between two computation units when they move from one place to another; because current network infrastructure and protocols are designed to support stationary commu-nication endpoints only. We have developed MOVE, a fine-grain end-to-end connection migration architec-ture, to address the problem. The most distinguishing characteristic of MOVE is that MOVE achieves, in a single system, several essential goals of a mobile commu-nication architecture including: (1) entirely end system only without any infra-structure demand, transport protocol independence, and backward compatibility; (2) fine-grain connection migration and unlimited mobility scope; (3) secure migration with both handoff and suspension/resumption support; and (4) very

We describe a method for implementing checkpoints on a UNIX � system. The method requires no special operating system support. The checkpoints (a term we use both for the act of saving state and the result) are created in the file system name space. Availability in the name space allows facilities to duplicate and transfer files to be applied; in this case, we get replicated processes and process migration rather naturally. We describe the process migration implementation. Our process migration implementation was easily optimized to achieve an execution speed improvement of greater than 7 times over our first implementation; this was accomplished by a combination of a faster file transfer mechanism and a change in the underlying protocol. We have incorporated the mechanism into a library routine, rfork(). We conclude with a discussion of advantages, limitations and applications of our approach. 1.

The Plan 9 window system, 8 1 /2 , is a modest-sized program of novel design. It provides ASCII I/O and bitmap graphic services to both local and remote client programs by offering a multiplexed file service to those clients. It serves traditional UNIX files like /dev/tty as well as more unusual ones that provide access to the mouse and the raw screen. Bitmap graphics operations are provided by serving a file called /dev/bitblt that interprets client messages to perform raster operations. The file service that 8 1 /2 offers its clients is identical to that it uses for its own implementation, so it is fundamentally no more than a multiplexer. This architecture has some rewarding symmetries and can be implemented compactly

ion : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 10 2.2.3 Interface and Code Sharing : : : : : : : : : : : : : : : : : : : : : : : : : : 10 2.2.4 Polymorphism : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 2.2.5 Design Sharing : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 2.2.6 Summary : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 12 3 Related Work : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 13 3.1 Survey of File Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 13 3.1.1 Record File Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 13 3.1.2 Byte-Stream File Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : 14 3.1.3 Object Storage Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15 3.1.4 Distributed File Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : 18 3.1.5 Summary : : : : :...