Voici les éléments 1 - 10 sur 66
- PublicationMétadonnées seulementRayNet : approximation de structures complexes pour la recherche de données multidimensionnelles à large échelle(2008-2-13)
;Beaumont, Olivier ;Kermarrec, Anne-Marie
- PublicationMétadonnées seulementCADA: Collaborative Auditing for Distributed Aggregation(2012-5-8)
;Valerio, José ; ;Rajman, MartinThe aggregation of distributions, composed of the number of occurrences of each element in a set, is an operation that lies at the heart of several large-scale distributed applications. Examples include popularity tracking, recommendation systems, trust management, or popularity measurement mechanisms. These applications typically span multiple administrative domains that do not trust each other and are sensitive to biases in the distribution aggregation: the results can only be trusted if inserted values were not altered nor forged, and if nodes collecting the insertions do not arbitrarily modify the aggregation results. In order to increase the level of trust that can be granted to applications, there must be a disincentive for servers to bias the aggregation results. In this paper we present the CADA auditing mechanisms that let aggregation servers collaboratively and periodically audit one another based on probabilistic tests over server-local state. CADA differs from the existing work on accountability in that it leverages the nature of the operation being performed by the node rather than a general and application-oblivious model of the computation. The effectiveness of CADA is conveyed by an experimental evaluation that studies its ability to detect malevolent behaviors using lightweight auditing oracles.
- PublicationMétadonnées seulementExploiting Concurrency in Domain-Specific Data Structures: A Concurrent Order Book and Workload Generator for Online Trading(2016-5-18)
; ; ;Concurrent programming is essential to exploit parallel processing capabilities of modern multi-core CPUs. While there exist many languages and tools to simplify the development of concurrent programs, they are not always readily applicable to domain-specific problems that rely on complex shared data structures associated with various semantics (e.g., priorities or consistency). In this paper, we explore such a domain-specific application from the financial field, where a data structure—an order book —is used to store and match orders from buyers and sellers arriving at a high rate. This application has interesting characteristics as it exhibits some clear potential for parallelism, but at the same time it is relatively complex and must meet some strict guarantees, notably w.r.t. the ordering of operations. We first present an accurate yet slightly simplified description of the order book problem and describe the challenges in paral- lelizing it. We then introduce several approaches for introducing concurrency in the shared data structure, in increasing order of sophistication starting from lock-based techniques to partially lock-free designs. We propose a comprehensive workload generator for constructing histories of orders according to realistic models from the financial domain. We finally perform an evaluation and comparison of the different concurrent designs.
- PublicationMétadonnées seulementFastLane: Streamlining Transactions for Low Thread Counts(2012)
;Wamhoff, Jons-Tobias ; ;Fetzer, Christof ;Muller, Gilles
- PublicationMétadonnées seulement
- PublicationMétadonnées seulementConfidentiality-Preserving Publish/Subscribe: A Survey(2016-6-30)
; ; ;Publish/subscribe (pub/sub) is an attractive communication paradigm for large-scale distributed applications running across multiple administrative domains. Pub/sub allows event-based information dissemination based on constraints on the nature of the data rather than on pre-established communication channels. It is a natural fit for deployment in untrusted environments such as public clouds linking applications across multiple sites. However, pub/sub in untrusted environments leads to major confidentiality concerns stemming from the content-centric nature of the communications. This survey classifies and analyzes different approaches to confidentiality preservation for pub/sub, from applications of trust and access control models to novel encryption techniques. It provides an overview of the current challenges posed by confidentiality concerns and points to future research directions in this promising field.
- PublicationMétadonnées seulementEvaluation of AMD's Advanced Synchronization Facility within a Complete Transactional Memory Stack(2010-4-13)
;Christie, Dave ;Chung, Jae-Woong ;Diestelhorst, Stephan ;Hohmuth, Michael ;Pohlack, Martin ;Fetzer, Christof ;Nowack, Martin ;Riegel, Torvald ; ;AMD's Advanced Synchronization Facility (ASF) is an x86 instruction set extension proposal intended to simplify and speed up the synchronization of concurrent programs. In this paper, we report our experiences using ASF for implementing transactional memory. We have extended a C/C++ compiler to support language-level transactions and generate code that takes advantage of ASF. We use a software fallback mechanism for transactions that cannot be committed within ASF (e.g., because of hardware capacity limitations). Our evaluation uses a cycle-accurate x86 simulator that we have extended with ASF support. Building a complete ASF-based software stack allows us to evaluate the performance gains that a user-level program can obtain from ASF. Our measurements on a wide range of benchmarks indicate that the overheads traditionally associated with software transactional memories can be significantly reduced with the help of ASF.
- PublicationMétadonnées seulementSlead: low-memory steady distributed systems slicing(: Springer, 2012-6-1)
;Maia, Francisco ;Matos, Miguel ;Oliveira, RuiSlicing a large-scale distributed system is the process of autonomously partitioning its nodes into k groups, named slices. Slicing is associated to an order on node-specific criteria, such as available storage, uptime, or bandwidth. Each slice corresponds to the nodes between two quantiles in a virtual ranking according to the criteria. For instance, a system can be split in three groups, one with nodes with the lowest uptimes, one with nodes with the highest uptimes, and one in the middle. Such a partitioning can be used by applications to assign different tasks to different groups of nodes, e.g., assigning critical tasks to the more powerful or stable nodes and less critical tasks to other slices. Assigning a slice to each node in a large-scale distributed system, where no global knowledge of nodes’ criteria exists, is not trivial. Recently, much research effort was dedicated to guaranteeing a fast and correct convergence in comparison to a global sort of the nodes. Unfortunately, state-of-the-art slicing protocols exhibit flaws that preclude their application in real scenarios, in particular with respect to cost and stability. In this paper, we identify steadiness issues where nodes in a slice border constantly exchange slice and large memory requirements for adequate convergence, and provide practical solutions for the two. Our solutions are generic and can be applied to two different state-of-the-art slicing protocols with little effort and while preserving the desirable properties of each. The effectiveness of the proposed solutions is extensively studied in several simulated experiments.
- PublicationMétadonnées seulementManaging collaborative feedback information for distributed retrieval(: ACM, 2008-1-13)
; ;Luu, Toan ;Rajman, MartinDespite the many research efforts invested recently in peer-to-peer search engines, none of the proposed system has reached the level of quality and efficiency of their centralized counterpart. One of the main reasons for this inferior performance is the difficulty to attract a critical mass of users that would make the peer-to-peer system truly competitive. We argue that decentralized search mechanisms should not aim at replacing existing engines, but instead complement them by adding novel functionalities that would be difficult to provide in a centralized manner. This paper introduces an example of such a complementary search mechanism and presents the design of a distributed collaborative system for leveraging user feedback and document/user profiling information.
- PublicationMétadonnées seulementGossip-Based Networking for Internet-Scale Distributed Systems(2011-1-26)
;Voulgaris, SpyrosIn the era of Internet-scale applications, an increasing number of services are distributed over pools of thousands to millions of networked computers. Along with the obvious advantages in performance and capacity, such a massive scale comes also with challenges. Continuous changes in the system become the norm rather than the exception, either because of inevitable hardware failures or merely due to standard maintenance and upgrading procedures. Rather than trying to impose rigid control on the massive pools of resources, we should equip Internet-scale applications with enough flexibility to work around inevitable faults. In that front, gossiping protocols have emerged as a promising component due to their highly desirable properties: self-healing, self-organizing, symmetric, immensely scalable, and simple. Through visiting a representative set of fundamental gossiping protocols, this paper provides insight on the principles that govern their behavior. By focusing on the rationale and incentives behind gossiping protocols, we introduce the reader to the alternative way of managing massive scale systems through gossiping, and we intrigue her or his interest to delve deeper into the subject by providing an extensive list of pointers.