Pangaea is a wide-area file system that supports data sharing among a community of widely distributed users. It is built on a symmetrically decentralized infrastructure that consists of commodity computers provided by the end users. Computers act autonomously to serve data to their local users. When possible, they exchange data with nearby peers to improve the system's overall performance, availability, and network economy. This approach is realized by aggressively creating a replica of a file whenever and wherever it is accessed. This paper presents

background transfers transfers of data that humans are not waiting for to improve availability, reliability, latency or consistency. However, given the rapid fluctuations of available network bandwidth and changing resource costs due to technology trends, hand tuning the aggressiveness of background transfers risks (1) complicating applications, (2) being too aggressive and interfering with other applications, and (3) being too timid and not gaining the benefits of background transfers. Our goal is for the operating system to manage network resources in order to provide a simple abstraction of near zero-cost background transfers. Our system, TCP Nice, can provably bound the interference inflicted by background flows on foreground flows in a restricted network model. And our microbenchmarks and case study applications suggest that in practice it interferes little with foreground flows, reaps a large fraction of spare network bandwidth, and simplifies application construction and deployment. For example, in our prefetching case study application, aggressive prefetching improves demand performance by a factor of three when Nice manages resources; but the same prefetching hurts demand performance by a factor of six under standard network congestion control.

Chain replication is a new approach to coordinating clusters of fail-stop storage servers. The approach is intended for supporting large-scale storage services that exhibit high throughput and availability without sacrificing strong consistency guarantees. Besides outlining the chain replication protocols themselves, simulation experiments explore the performance characteristics of a prototype implementation. Throughput, availability, and several objectplacement strategies (including schemes based on distributed hash table routing) are discussed.

The emerging edge services architecture promises to improve the availability and performance of web services by replicating servers at geographically distributed sites. A key challenge in such systems is data replication and consistency so that edge server code can manipulate shared data without incurring the availability and performance penalties that would be incurred by accessing a traditional centralized database. This paper explores using a distributed object architecture to build an edge service system for an e-commerce application, an online bookstore represented by the TPC-W benchmark. We take advantage of application specific semantics to design distributed objects to manage a specific subset of shared information using simple and effective consistency models. Our experimental results show that by slightly relaxing consistency within individual distributed objects, we can build an edge service system that is highly available and efficient. For example, in one experiment we find that our object-based edge server system provides a factor of five improvement in response time over a traditional centralized cluster architecture and a factor of nine improvement over an edge service system that distributes code but retains a centralized database.

We present PRACTI, a new approach for large-scale replication. PRACTI systems can replicate or cache any subset of data on any node (Partial Replication), provide a broad range of consistency guarantees (Arbitrary Consistency), and permit any node to send information to any other node (Topology Independence). A PRACTI architecture yields two significant advantages. First, by providing all three PRACTI properties, it enables better trade-offs than existing mechanisms that support at most two of the three desirable properties. The PRACTI approach thus exposes new points in the design space for replication systems. Second, the flexibility of PRACTI protocols simplifies the design of replication systems by allowing a single architecture to subsume a broad range of existing systems and to reduce development costs for new ones. To illustrate both advantages, we use our PRACTI prototype to emulate existing server replication, client-server, and object replication systems and to implement novel policies that improve performance for mobile users, web edge servers, and grid computing by as much as an order of magnitude.

We introduce the hash history mechanism for capturing dependencies among distributed replicas. Hash histories, consisting of a directed graph of version hashes, are independent of the number of active nodes but dependent on the rate and number of modifications. We present the basic hash history scheme and discuss mechanisms for trimming the history over time. We simulate the efficacy of hash histories on several large CVS traces. Our results highlight a useful property of the hash history: the ability to recognize when two different non-commutative operations produce the same output, thereby reducing false conflicts and increasing the rate of convergence. We call these events coincidental equalities and demonstrate that their recognition can greatly reduce the time to global convergence.

Today, the utility of many replicated Internet services is limited by availability rather than raw performance. To better understand the effects of replica placement on availability, we propose the problem of minimal replication cost for availability. Let replication cost be the cost associated with replica deployment, dynamic replica creation and teardown at n candidate locations. Given client access patterns, replica failure patterns, network partition patterns, a required consistency level and a target level of availability, the minimal replication cost is the lower bound on a system's replication cost. Solving this problem also answers the dual question of optimal availability given a constraint on replication cost.

optimistic, replication, survey Replication is a key enabling technology in distributed data sharing systems for improving both availability and performance. This paper surveys optimistic replication algorithms, which allow replica contents to diverge in the short term, in order to support concurrent work and to tolerate failures in low-quality communication links. The importance of such techniques is increasing as collaboration through wide-area and mobile networks is becoming more popular. Optimistic replication algorithms employ techniques vastly different from those for traditional pessimistic algorithms. Whereas a pessimistic algorithm relies on synchronous

Information integrity policies are traditionally enforced by access control mechanisms that prevent unauthorized users from modifying data. However, access control does not provide end-to-end assurance of integrity. For that reason, integrity guarantees in the form of noninterference assertions have been proposed. Despite the appeals of such information-flow based approaches to integrity, that solution is also unsatisfactory because it leads to a weaker notion of integrity than needed in practice. This paper

Abstract. This paper describes Transparent Replication through Invalidation and Prefetching (TRIP), a self tuning data replication middleware system that enables transparent replication of large-scale information dissemination services. The TRIP middleware is a key building block for constructing information dissemination services, a class of services where updates occur at an origin server and reads occur at a number of replicas; examples information dissemination services include content distribution networks such as Akamai [1] and IBM’s Sport and Event replication system [2]. Furthermore, the TRIP middleware can be used to build key parts of general applications that distribute content such as file systems, distributed databases, and publish-subscribe systems. Our data replication middleware supports transparent replication by providing two crucial properties: (1) sequential consistency to avoid introducing anomalous behavior to increasingly complex services and (2) selftuning transmission of updates to maximize performance and availability given available system resources. Our analysis of simulations and our evaluation of a prototype support the hypothesis that it is feasible to provide transparent replication for dissemination services. For example, in simulations, our system’s performance is a factor of three to four faster than a demand-based middleware system for a wide range of configurations. 1