This paper presents Sharp, a framework for secure distributed resource management in an Internet-scale computing infrastructure. The cornerstone of Sharp is a construct to represent cryptographically protected resource claims— promises or rights to control resources for designated time intervals—together with secure mechanisms to subdivide and delegate claims across a network of resource managers. These mechanisms enable flexible resource peering: sites may trade their resources with peering partners or contribute them to a federation according to local policies. A separation of claims into tickets and leases allows coordinated resource management across the system while preserving site autonomy and local control over resources. Sharp also introduces mechanisms for controlled, accountable oversubscription of resource claims as a fundamental tool for dependable, efficient resource management. We present experimental results from a Sharp prototype for PlanetLab, and illustrate its use with a decentralized barter economy for global PlanetLab resources. The results demonstrate the power and practicality of the architecture, and the effectiveness of oversubscription for protecting resource availability in the presence of failures.

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.

Replication is a well-known technique to improve the accessibility of Web sites. It generally offers reduced client latencies and increases a site’s availability. However, applying replication techniques is not trivial, and various Content Delivery Networks (CDNs) have been created to facilitate replication for digital content providers. The

This paper presents the design, implementation, and evaluation of Colyseus, a distributed architecture for interactive multiplayer games. Colyseus takes advantage of a game’s tolerance for weakly consistent state and predictable workload to meet the tight latency constraints of game-play and maintain scalable communication costs. In addition, it provides a rich distributed query interface and effective pre-fetching subsystem to help locate and replicate objects before they are accessed at a node. We have implemented Colyseus and modified Quake II, a popular first person shooter game, to use it. Our measurements of Quake II and our own Colyseus-based game with hundreds of players shows that Colyseus effectively distributes game traffic across the participating nodes, allowing Colyseus to support low-latency game-play for an order of magnitude more players than existing single server designs, with similar per-node bandwidth costs. 1

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.

Abstract. In this paper, we present GlobeCBC, a content-blind query caching middleware for hosting Web applications in an edge computing infrastructure. Unlike existing data caching middleware systems, GlobeCBC stores the query results independently and does not merge different query results. We study the potential performance of this approach using extensive experimentations on our prototype implementation and compare it with other systems over an emulated wide-area network. Our evaluations show that content-blind caching performs well in terms of client latency for applications that exhibit high locality. It allows the system to sustain higher throughput by offloading the origin server database. We also present the design and evaluation of different online cache replacement algorithms for edge servers that have limited resource capabilities. In our evaluations, we find that the best heuristic must exploit temporal locality and take into Edge service architectures have become the most widespread platform for distributing Web content over the Internet. Commercial Content Delivery Networks (CDNs) like

A data grid is a collection of geographically dispersed storage resources over wide area network. The goal of data grid system is to provide a large virtual storage framework with unlimited power through collaboration among individuals, institutions, and resources. In this study, we first review a number of data grid services such as, to just name a few, metadata service, data access service, and performance measurement service. We then investigate various techniques for boosting the performance of data grid, and these key techniques have fallen into three camps, namely, data replication, scheduling, and data movement. Since security issue becomes one of the prime concerns in grid computing, we review two interesting issues of security in data grid. Finally and importantly, we have identified five interesting open issues, and pointed out some potential solutions to the open problems.

Abstract. In this paper we address the problem of consistency for cryptographic file systems. A cryptographic file system protects the users ’ data from the file server, which is possibly untrusted and might exhibit Byzantine behavior, by encrypting the data before sending it to the server. The consistency of the encrypted file objects that implement a cryptographic file system relies on the consistency of the two components used to implement them: the file storage protocol and the key distribution protocol. We first define two generic classes of consistency conditions that extend and generalize existing consistency conditions. We then formally define consistency for encrypted file objects in a generic way: for any consistency conditions for the key and file objects belonging to one of the two classes of consistency conditions considered, we define a corresponding consistency condition for encrypted file objects. We finally provide, in our main result, necessary and sufficient conditions for the consistency of the key distribution and file storage protocols under which the encrypted storage is consistent. Our framework allows the composition of existing key distribution and file storage protocols to build consistent encrypted file objects and simplifies complex proofs for showing the consistency of encrypted storage. 1

This paper introduces a new consistency metric, Network Imprecision (NI), to address a central challenge in largescale monitoring systems: safeguarding correctness despite node and network failures. To implement NI, an overlay that monitors a set of attributes also monitors its own state so that queries return not only attribute values but also information about the stability of the overlay—the number of nodes whose recent updates may be missing and the number of nodes whose inputs may be double counted due to overlay reconfigurations. When NI indicates that the network is stable, query results reflect the true state of the system, but when the network is unstable, NI puts applications on notice that query results should not be trusted, allowing them to take corrective action such as filtering out inconsistent results. To implement NI’s introspection scalably, our prototype introduces a key optimization, dual-tree prefix aggregation, which exploits overlay symmetry to reduce overheads by more than an order of magnitude. Evaluation of three monitoring applications demonstrates that NI flags inaccurate results while incurring low overheads, and monitoring applications that use NI to select good information can reduce their inaccuracy by nearly a factor of five.

Many replication mechanisms for large scale distributed systems exist, but they require a designer to compromise a system's replication policy (e.g., by requiring full replication of all data to all nodes), consistency policy (e.g., by supporting per-object coherence but not multiobject consistency), or topology policy (e.g., by assuming a hierarchical organization of nodes.) In this paper, we present the first PRACTI (Partial Replication, Arbitrary Consistency, and Topology Independence) mechanisms for replication in large scale systems. These new mechanisms allow construction of systems that replicate or cache any data on any node, that provide a broad range of consistency and coherence guarantees, and that permit any node to communicate with any other node at any time. Our evaluation of a prototype suggests that by disentangling mechanism from policy, PRACTI replication enables better trade-offs for system designers than possible with existing mechanisms. For example, for one workload we study, PRACTI's partial replication reduces bandwidth requirements by over an order of magnitude compared to full replication for nodes that only care about a subset of the system's data.