Oracle File Storage Service (FSS) is an elastic filesystem provided as a managed NFS service. A pipelined Paxos implementation underpins a scalable block store that provides linearizable multipage limited-size transactions. Above the block store, a scalable B-tree holds filesystem metadata and provides linearizable multikey limited-size transactions. Self-validating B-tree nodes and housekeeping operations performed as separate transactions allow each key in a B-tree transaction to require only one page in the underlying block transaction. The filesystem provides snapshots by using versioned key-value pairs. The system is programmed using a nonblocking lock-free programming style. Presentation servers maintain no persistent local state making them scalable and easy to failover. A non-scalable Paxos-replicated hash table holds configuration information required to bootstrap the system. An additional B-tree provides conversational multi-key minitransactions for control-plane information. The system throughput can be predicted by comparing an estimate of the network bandwidth needed for replication to the network bandwidth provided by the hardware. Latency on an unloaded system is about 4 times higher than a Linux NFS server backed by NVMe, reflecting the cost of replication. FSS has been in production since January 2018 and holds tens of thousands of customer file systems comprising many petabytes of data.

Mobile devices are ubiquitous but their resources are limited. However, they must be capable to run computationally intensive software, for example for image stitching, face recognition, and simulation-based artificial intelligence. As a solution, mobile devices can use nearby resources to offload computation. Distributed computing environments provide such features but ignore the nature of mobile devices, such as mobility, network, or battery changes. This leads to long delays, which reduce the quality of experience for the user. In this paper, we present Mobile Tasklets, a mobile extension of our distributed computing middleware. The design of Mobile Tasklets includes context monitoring, context-aware scheduling mechanisms, and an Android API for application integration. We identify the challenges of the integration of mobile devices into our distributed computing environment. We evaluate Mobile Tasklets in a realworld testbed with different context settings.

The modern computing landscape consists of numerous heterogeneous devices, all of which can contribute to a distributed environment as generic computation resources. In unstructured environments, resources can easily be shared and consumed at the cost of certainty. While some applications can handle such a best-effort service, many others require execution qualities, e.g., reliability or speed. We introduce Quality of Computation (QoC) as a thin layer on top of uniformly abstracted best-effort resources, which allows to tailor computation tasks to application-specific needs. The QoC layer provides execution guarantees for reliability, speed, precision, privacy, cost, and energy. We demonstrate QoC on the basis of the Tasklet system. Tasklets are fine-grained units of computation that can be issued for local or remote execution. The Tasklet system has two layers. Below is the best-effort execution layer, a virtual machine that provides raw computation. Above is the orchestration layer, which federates these virtual machines to one distributed computing environment and enforces the mechanisms that guarantee the requested QoC. We evaluated the performance of QoC in the Tasklet system in various scenarios. Results indicate that our system provides QoC guarantees at minimal performance cost.

On the desktop, users are accustomed to having visible handles to objects that they want to organize, share, or manipulate. Web applications today feature many classes of such objects, like flight itineraries, products for sale, people, recipes, and businesses, but there are no interoperable handles for high-level semantic objects that users can grab. This paper proposes Clui, a platform for exploring a new data type, called a Webit, that provides uniform handles to rich objects. Clui uses plugins to 1) create Webits on existing pages by extracting semantic data from those pages, and 2) augmenting existing sites with drag and drop targets that accept and interpret Webits. Users drag and drop Webits between sites to transfer data, auto-fill search forms, map associated locations, or share Webits with others. Clui enables experimentation with handles to semantic objects and the standards that underlie them.

We present ChunkStream, a system for efficient streaming and interactive editing of online video. Rather than using a specialized protocol and stream format, ChunkStream makes use of a generic mechanism employing chunks. Chunks are fixed-size arrays that contain a mixture of scalar data and references to other chunks. Chunks allow programmers to expose large, but fine-grained, data structures over the network. ChunkStream represents video clips using simple data types like linked lists and search trees, allowing a client to retrieve and work with only the portions of the clips that it needs. ChunkStream supports resource-adaptive playback and “live” streaming of real-time video as well as fast, frame-accurate seeking; bandwidth-efficient high-speed playback; and compilation of editing decisions from a set of clips. Benchmarks indicate that ChunkStream uses less bandwidth than HTTP Live Streaming while providing better support for editing primitives.

Debugging pervasive applications is difficult due to their distributed, asynchronous, and dynamic nature. To help ease the debugging process, we propose PerViz, a developer-targeted tool that enhances system visibility through real-time visualizations of system state, semi-automates application restarts and positioning, and enables both real-time and asynchronous collaboration in debugging between developers. Developers interact with PerViz through a web browser, which provides a convenient, centralized location to study and filter aggregated application debugging logs and state. In our experience with using PerViz, we have found its log aggregation and real-time visualizations to be key facilitators for effective debugging.

Effective security mechanisms are essential to the widespread deployment of pervasive systems. Much of the research focus on security in pervasive computing has revolved around distributed trust management. While such mechanisms are effective in specific environments, there is no generic framework for deploying and extending these mechanisms over a variety of pervasive systems. We present the design and implementation of a novel framework called distributed trust toolkit (DTT), for implementing and evaluating trust mechanisms in pervasive systems. The DTT facilitates the extension and adaptation of trust mechanisms by abstracting trust mechanisms into interchangeable components. Furthermore, the DTT provides a set of tools and interfaces to ease implementation of trust mechanisms and facilitate their execution on a variety of platforms and networks. In addition to the adaptability and extensibility provided by this design, we demonstrate through simulation that use of DTT improves utilization of resources and enhances performance of existing trust mechanisms in pervasive systems. We are currently developing an implementation of the DTT that can be easily deployed in pervasive environments.

We present a middleware platform for assembling pervasive applications that demand fault-tolerance and adaptivity in distributed, dynamic environments. Unlike typical adaptive middleware approaches, in which sophisticated component model semantics are embedded into an existing, underlying platform (e.g., CORBA, COM, EJB), we propose a platform that imposes minimal constraints for greater flexibility. Such a tradeoff is advantageous when the platform is targeted by automatic code generators that inherently enforce correctness by construction. Applications are written as simple, single-threaded programs that assemble and monitor a set of distributed components. The approach decomposes applications into two distinct layers: (1) a distributed network of interconnected modules performing computations, and (2) constructor logic that assembles that network via a simple block-diagram construction API. The constructor logic subsequently monitors the configured system via a stream of high-level events, such as notifications of resource availability or failures, and consequently provides a convenient, centralized location for reconfiguration and debugging. The component network is optimized for performance, while the construction API is optimized for ease of assembly.

We describe an approach to automate certain high- level implementation decisions in a pervasive application, allowing them to be postponed until run time. Our system enables a model in which an application programmer can specify the behavior of an adaptive application as a set of open-ended decision points. We formalize decision points as goals, each of which may be satisfied by a set of scripts called Techniques. The set of Techniques vying to satisfy any goal is additive and may be extended at runtime without needing to modify or remove any existing techniques. Our system provides a framework in which Techniques may compete and interoperate at runtime in order to maintain an adaptive application. Technique development may be distributed and incremental, providing a path for the decentralized evolution of applications. Benchmarks show that our system imposes reasonable overhead during application startup and adaptation.

This paper presents the design and implementation of service-oriented network sockets (SoNS) for accessing services in a dynamically changing networked environment. A service-oriented network socket takes a high-level description of a service and opportunistically connects to the best provider of that service in the changing characteristics of a mobile system. An application states its high-level service requirements as a set of constraints on the properties required in a suitable resource and SoNS continuously monitors, evaluates and compares the available resources and (re-)connects to the resource that best satisfies the specified constraints. Unlike content-based routing systems, SoNS is an endhost system, interposed at the session-binding layer, and offers connection-oriented semantics. SoNS ’ interface allows an application to tailor the planning policy used to establish and rebind a network session. SoNS is based on an extensible architecture to leverage the wide-range of emerging technologies for discovering and locating resources in a mobile system. SoNS integrates a service-oriented abstraction with the traditional operating system interface for accessing network services, making it simpler to develop pervasive, mobile applications. We present an implementation for a mobile handheld device, analyze the performance of our system and describe an application to demonstrate the utility of our system. 1