The MOSIX Direct File System Access Method for Supporting Scalable Cluster File Systems

MOSIX is a cluster management system that supports preemptive process migration. This paper presents the MOSIX Direct File System Access (DFSA), a provision that can improve the performance of cluster file systems by allowing a migrated process to directly access files in its current location. This capability, when combined with an appropriate file system, could substantially increase the I/O performance and reduce the network congestion by migrating an I/O intensive process to a file server rather than the traditional way of bringing the file's data to the process. DFSA is suitable for clusters that manage a pool of shared disks among multiple machines. With DFSA, it is possible to migrate parallel processes from a client node to file servers for parallel access to different files. Any consistent file system can be adjusted to work with DFSA. To test its performance, we developed the MOSIX File-System (MFS) which allows consistent parallel operations on different files. The paper describes DFSA and presents the performance of MFS with and without DFSA.     

Scalable Session Locking for a Distributed File System

File systems provide an interface for applications to obtain exclusive access to files, in which a process holds privileges to a file that cannot be preempted and restrict the capabilities of other processes. Local file systems do this by maintaining information about the privileges of current file sessions, and checking subsequent sessions for compatibility. Implementing exclusive access in this manner for distributed file systems degrades performance by requiring every new file session to be registered with a lock server that maintains global session state. We present two techniques for improving the performance of session management in the distributed environment. We introduce a distributed lock for managing file access, called a semi-preemptible lock, that allows clients to cache privileges. Under a semi-preemptible lock, a file system creates new sessions without messages to the lock manager. This improves performance by exploiting locality – the affinity of files to clients. We also present data structures and algorithms for the dynamic evaluation of locks that allow a distributed file system to efficiently manage arbitrarily complex locking. In this case, complex means that an object can be locked in a large number of unique modes. The combination of these techniques results in a distributed locking scheme that supports fine-grained concurrency control with low memory and message overhead and with the assurance that their locking system is correct and avoids unnecessary deadlocks.     

The Rutgers Computational Grid: A Distributed Linux PC Cluster

The Rutgers Computational Grid (RCG) project is aimed at providing high throughput performance to Rutgers university faculty and students. The RCG employs dual processor PCs, with Pentium II and III processors, as computational nodes, running the Linux RedHat operating system. The Load Sharing Facility (LSF) scheduling system from Platform Computing is used for job control and monitoring. The nodes are grouped into subclusters physically located in several departments and controlled by a single master node through LSF. The hardware and software used in RCG are described. Utilization and performance issues, including parallel performance, are discussed based on the experience of the first two years of RCG operation.     

Seamless Access to Decentralized Storage Services in Computational Grids via a Virtual File System

This paper describes a novel technique for establishing a virtual file system that allows data to be transferred user-transparently and on-demand across computing and storage servers of a computational grid. Its implementation is based on extensions to the Network File System (NFS) that are encapsulated in software proxies. A key differentiator between this approach and previous work is the way in which file servers are partitioned: while conventional file systems share a single (logical) server across multiple users, the virtual file system employs multiple proxy servers that are created, customized and terminated dynamically, for the duration of a computing session, on a per-user basis. Furthermore, the solution does not require modifications to standard NFS clients and servers. The described approach has been deployed in the context of the PUNCH network-computing infrastructure, and is unique in its ability to integrate unmodified, interactive applications (even commercial ones) and existing computing infrastructure into a network computing environment. Experimental results show that: (1) the virtual file system performs well in comparison to native NFS in a local-area setup, with mean overheads of 1 and 18%, for the single-client execution of the Andrew benchmark in two representative computing environments, (2) the average overhead for eight clients can be reduced to within 1% of native NFS with the use of concurrent proxies, (3) the wide-area performance is within 1% of the local-area performance for a typical compute-intensive PUNCH application (SimpleScalar), while for the I/O-intensive application Andrew the wide-area performance is 5.5 times worse than the local-area performance.     

A System for Distributed Storage and Analysis of Genome Information

A distributed computing system is developed to search and analyze genetic databases using parallel computing technologies. Queries are processed by a local network PC cluster. A universal task and data exchange format is developed for effective query processing. A multilevel hierarchic task batching procedure is elaborated to generate multiple subtasks and distribute them over cluster units under dynamic priority levels and with dynamic distribution of replicated source data subbases. Primary source data preparation and generation of annotation word indices are used to significantly reduce query processing time.     

Multiple Bypass: Interposition Agents for Distributed Computing

Interposition agents are a well-known device for attaching legacy applications to distributed systems. However, agents are difficult to build and are often large, monolithic pieces of software which are suited only to limited applications or systems. We solve this problem with Bypass, a language and a tool for quickly building multiple small agents that can be combined together to create powerful yet manageable software.     

Programming the Grid: Distributed Software Components, P2P and Grid Web Services for Scientific Applications

Computational Grids [17,25] have become an important asset in large-scale scientific and engineering research. By providing a set of services that allow a widely distributed collection of resources to be tied together into a relatively seamless computing framework, teams of researchers can collaborate to solve problems that they could not have attempted before. Unfortunately the task of building Grid applications remains extremely difficult because there are few tools available to support developers. To build reliable and re-usable Grid applications, programmers must be equipped with a programming framework that hides the details of most Grid services and allows the developer a consistent, non-complex model in which applications can be composed from well tested, reliable sub-units. This paper describes experiences with using a software component framework for building Grid applications. The framework, which is based on the DOE Common Component Architecture (CCA) [1,2,3,8], allows individual components to export function/service interfaces that can be remotely invoked by other components. The framework also provides a simple messaging/event system for asynchronous notification between application components. The paper also describes how the emerging Web-services [52] model fits with a component-oriented application design philosophy. To illustrate the connection between Web services and Grid application programming we describe a simple design pattern for application factory services which can be used to simplify the task of building reliable Grid programs. Finally we address several issues of Grid programming that better understood from the perspective of Peer-to-Peer (P2P) systems. In particular we describe how models for collaboration and resource sharing fit well with many Grid application scenarios.     

实时虚拟导航系统辅助超声引导下消融治疗肝癌患者疗效与安全性的系统评价

目的:系统评价实时虚拟导航系统辅助超声引导下射频消融治疗肝癌患者疗效与安全性,为临床治疗提供参考.方法:计算机检索Pubmed、EMbase、The Cochrane Library、Web of Science、WanFang Data、CNKI、CBM、VIP 数据库,同时辅以其他检索,收集所有相关的临床对照试验,...