. Developing large-scale wide-area applications requires an infrastructure that is presently lacking entirely. Currently, applications have to be built on top of raw communication services, such as TCP connections. All additional services, including those for naming, replication, migration, persistence, fault tolerance, and security, have to be implemented for each application anew. Not only is this a waste of effort, it also makes interoperability between different applications difficult or even impossible. We present a novel, object-based framework for developing wide-area distributed applications. The framework is based on the concept of a distributed shared object, which has the characteristic feature that its state can be physically distributed across multiple machines at the same time. All implementation aspects, including communication protocols, replication strategies, and distribution and migration of state, are part of an object and are hidden behind its interface. The curren...

We present a new file system that combines name-based and content-based access to files at the same time. Our design allows both methods to be used at any time, thus preserving the benefits of both. Users can create their own name spaces based on queries, on explicit path names, or on any combination interleaved arbitrarily. All regular file operations -- such as adding, deleting, or moving files -- are supported in the same way, and in addition, query consistency is maintained and adapted to what the user is manually doing. One can add, remove, or move results of queries, and in general handle them as if they were regular files. This creates interesting new consistency problems, for which we suggest and implement solutions. Remote le systems or remote query systems (e.g., web search) can be integrated by users into their own coherent name spaces in a clean way. We believe that our design can serve as the basis for the future information-rich file systems, allowing users better handle on their information.

The Global File System (GFS) is a prototype design for a distributed file system in which cluster nodes physically share storage devices connected via a network like Fibre Channel. Networks and network attached storage devices have advanced to a level of performance and extensibility that the once believed disadvantages of “shared disk ” architectures are no longer valid. This shared storage architecture attempts to exploit the sophistication of device technologies where as the client–server architecture diminishes a device’s role to a simple components. GFS distributes the file system responsibilities across the processing nodes, storage across the devices, and file system resources across the entire storage pool. GFS caches data on the storage devices instead of the main memories of the machines. Consistency is established by using a locking mechanism maintained by the storage device controllers to facilitate atomic read–modify– write operations. The locking mechanism is being prototyped on Seagate disks drives and Ciprico disk arrays. GFS is implemented in the Silicon Graphics IRIX operating system and is accessed using standard Unix commands and utilities.

Mobile Computing is a new emerging computing paradigm of the future. Data Management in this paradigm poses many challenging problems to the database community. In this paper we identify these new challenges and plan to investigate their technical significance. New research problems include management of location dependent data, wireless data broadcasting, disconnection management and energy efficient data access. 1 Introduction The rapidly expanding technology of cellular communications, wireless LAN, wireless data networks, and satellite services will give mobile users capability of accessing information anywhere and anytime. In the near future, tens of millions of users will carry a portable (palmtop, laptop) computer (often called personal digital assistant (PDA) or personal communicator) with wireless connection to a worldwide information network. Coming years will most likely be the decade of mobile or nomadic computing. This vision poses new challenging problems to the databas...

Mobile computing is a new emerging computing paradigm posing many challenging data management problems. We identify these new challenges and investigate their technical significance. New research problems include management of location dependent data, frequent disconnections, structuring distributed algorithms for mobile hosts, wireless data broadcasting, and energy efficient data access. 1 Introduction The rapidly expanding technology of cellular communications, wireless LAN, and satellite services will make it possible for mobile users to access information anywhere and at anytime. In the near future, tens of millions of users will carry a portable computer often called a personal digital assistant or a personal communicator. Various possibilities are shown in Figure 1. Smaller units will run on AA batteries and may be diskless; larger units will run on Ni-Cd packs. These will be powerful laptop computers with large memories and powerful processors. Regardless of size, all mobile co...

Current wide area distributed systems fail to hide implementation aspects related to the distribution of information. Unfortunately, the solutions developed for local systems do not scale, so a different approach is needed. In this paper we present an architecture for distributed systems that scales to support a large number of users and objects. The architecture is based on the concept of distributed shared objects, which are used for sharing and exchanging information over wide area networks. Our architecture provides location and replication transparency, and offers the flexibility needed to cope with the heterogeneity inherent in wide area systems.

In this paper we present a new storage architecture for clusters that creates a shared memory of disk storage that is uniformly accessible to all cluster clients, scales to large capacity, and provides very high performance and connectivity. The cluster structure resembles a symmetric multiprocessor (SMP) in that clients (processors) can access disk data (memory) across a local area network like Fibre Channel (a bus or other interconnection network). All clients can see and access the same disk data with perfect consistency. Our approach avoids buffer copy overheads and server bottlenecks found in traditional file systems while scaling to potentially large numbers of clients and large capacity disk systems.

Group communication is an important paradigm for building distributed applications. This paper discusses a fault-tolerant distributed directory service based on group communication, and compares it with the previous design and implementation based on remote procedure call. The group directory service uses an active replication scheme and, when triplicated, can handle 627 lookup operations per second and 88 update operations per second (using nonvolatile RAM). This performance is better than the performance for the RPC implementation and it is even better than the performance for directory operations under SunOS, which does not provide any fault tolerance at all. The paper concludes that the implementation using group communication is simpler and has better performance than the one based on remote procedure call, supporting the claim that a distributed operating system should provide both remote procedure call and group communication.

This article proposes a scalable protocol for replication management in large-scale replicated systems. The protocol organizes sites and data replicas into a tree-structured, hierarchical cluster architecture. The basic idea of the protocol is to accomplish the complex task of updating replicated data with a very large number of replicas by a set of related but independently committed transactions. Each transaction is responsible for updating replicas in exactly one cluster and invoking additional transactions for member clusters. Primary copies (one from each cluster) are updated by a cross-cluster transaction. Then each cluster is independently updated by a separate transaction. This decoupled update propagation process results in possible multiple views of replicated data in a cluster. Compared to other replicated data management protocols, the proposed protocol has several unique advantages. First, thanks to a smaller number of replicas each transaction needs to atomically update in a cluster, the protocol significantly reduces the transaction abort rate, which tends to soar in large transactional systems. Second, the protocol improves user-level transaction response time as top-level update transactions are allowed to commit before all replicas have been updated. Third, read-only queries have the flexibility to see database views of different degrees of consistency and data currency. This ranges from global, most up to date, and consistent views, to local, consistent, but potentially old views, to local, nearest to users but potentially inconsistent views. Fourth, the protocol maintains its scalability by allowing dynamic system reconfiguration as it grows by splitting a cluster into two or more smaller ones. Fifth, autonomy of the clusters is preserved as no speci...

The recent proliferation of portable computers, the advent of personal digital assistants (PDAs) and continuing advances in computer networking all point to a future in which mobility of both users and computing system elements will be standard. However, these developments also invalidate many of the assumptions made by current system software, which has been built for stationary systems and users. An important component of system software that needs to looked at afresh is the file system. A user should be able to access the files he or she needs regardless of location. Although existing research efforts do provide some support for this, there are significant deficiencies that need to be remedied. We propose two related designs to address these problems. The first exploits the unique property of a PDA that it can accompany its owner at all times by using it to carry files of most immediate need to him or her. The second makes use of the recently proposed idea of a computing persona. ...