Browsing by Author "Keleher, Peter J."

Now showing 1 - 6 of 6
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    Decentralized Replication Mechanisms in Deno
    (1998-10-20) Keleher, Peter J.
    We are currently finalizing the design of Deno, a new shared-object system intended for use with repli-cated mobile and wide-area data. The broad aim of our research is to develop a framework for highly-available, decentralized shared-object protocols. The key idea is that our protocols will support high availability through a distributed voting scheme. Specifically, we will investigate (a) peer-to-peer up-dates, which will allow incremental progress to be made in the absence of full connectivity between com-ponent servers, (b) voting rather than centralized schemes for committing updates, ensuring that no sin-gle point of failure can prevent updates from being committed, and (c) application-specific consistency control, allowing applications to relax coherency constraints in ways that do not break the application's notion of consistency. Distribution and multiple connectivity modes are becoming the norm rather than the exception in current computing environments. Thus, we expect the impact of our research to be felt in areas as disparate as mobile computing and collaborative data warehousing on the Internet. (Also cross-referenced as UMIACS-TR-98-54)
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    Matching Jobs to Resources in Distributed Desktop Grid Environments
    (2006-04) Kim, Jik-Soo; Bhattacharjee, Bobby; Keleher, Peter J.; Sussman, Alan
    Desktop grids use opportunistic sharing to exploit large collections of personal computers and workstations across the Internet and can achieve tremendous computing power with low cost. However, current systems are typically based on a traditional client-server architecture, which has inherent shortcomings with respect to robustness, reliability and scalability. In this paper, we propose a decentralized, robust, highly available, and scalable infrastructure to match incoming jobs to available resources. The key idea behind our proposed system is to leverage information provided by an underlying peer-to-peer system to create a hierarchical Rendezvous Node Tree, which performs the matching efficiently. Our experimental results obtained via simulation show that we can effectively match jobs with varying levels of resource constraints to available nodes and maintain good load balance in a fully decentralized heterogeneous computational environment.
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    Rate Windows for Efficient Network and I/O Throttling
    (2000-07-12) Ryu, Kyung D.; Hollingsworth, Jeffrey K.; Keleher, Peter J.
    This paper proposes and evaluates a new mechanism for I/O and network rate policing. The goal of the proposed system is to provide an simple, yet effective way to enforce resource limits on target classes of jobs in a system. The basic approach is useful for several types of systems including running background jobs on idle workstations, and providing resource limits on network intensive applications such as virtual web server hosting. Our approach is quite simple, we use a sliding window average of recent events to compute the average rate for a target resource. The assigned limit is enforced by forcing application processes to sleep when they issue requests that would bring their resource utilization out of the allowable profile. Our experimental results that show that we are able to provide the target resource limitations within a few percent, and do so with no measurable slowdown of the overall system. (Also cross-referenced as UMIACS-TR-2000-53)
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    A Security Infrastructure for Mobile Transactional Systems
    (2000-07-11) Keleher, Peter J.; Bhattacharjee, Bobby; Kuo, Kuo-Tung; Cetintemel, Ugur
    In this paper, we present an infrastructure for providing secure transactional support for mobile databases. Our infrastructure protects against external threats - malicious actions by nodes not authorized to access the data. The major contribution of this paper, however, is to classify and present algorithms to protect against internal security threats. Internal threats are malicious ac-tions by authenticated nodes that misrepresent protocol specific information. We quantify the cost of our security mechanisms in context of Deno: a system that supports object replication in a transactional framework for mobile and weakly-connected environments. Our results show that protecting against internal threats comes at a cost, but the marginal cost for protecting against larger cliques of malicious insiders is low. However, even with all the security mechanisms in place, our system commits updates over 50% faster than systems that depend on the Read-once Write-all commit protocol. Lastly, we present results from a probabilistic version of our algorithm that has several orders of magnitude lower computation cost than the traditional public-key based schemes. (Also cross-referenced as UMIACS-TR-2000-19)
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    A Security Infrastructure for Mobile Transactional Systems
    (2000-08-16) Cetintemel, Ugur; Keleher, Peter J.; Bhattacharjee, Bobby
    In this paper, we present an infrastructure for providing secure transactional replication support for peer-to-peer, decentralized databases. We first describe how to effectively provide protection against external threats, malicious actions by servers not authorized to access data, using conventional cryp-tography-based mechanisms. We then classify and present algorithms that provide protection against internal threats, malicious actions by authenticated servers that misrepresent protocol-specific infor-mation. Our approach to handling internal threats uses both cryptographic techniques and modifica-tions to the update commit criteria. The techniques we propose are unique in that they not only enable a tradeoff between performance and the degree of tolerance to malicious servers, but also allow for indi-vidual servers to support non-uniform degrees of tolerance without adversely affecting the performance of the rest of the system. We investigate the cost of our security mechanisms in the context of Deno: a prototype object replica-tion system designed for use in mobile and weakly-connected environments. Experimental results reveal that protecting against internal threats comes at a cost, but the marginal cost for protecting against larger cliques of malicious insiders is generally low. Furthermore, comparison with a decentralized Read-One Write-All protocol shows that our approach performs significantly better under various workloads. (Also cross-referenced as UMIACS-TR-2000-59)
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    Support for Speculative Update Propagation and Mobility in Deno
    (2000-07-11) Cetintemel, Ugur; Keleher, Peter J.; Franklin, Michael
    This paper presents the transactional framework of Deno, an object replication system specifically designed for use in mobile and weakly-connected environments. Deno uses weighted voting for availability and pair-wise, epidemic information flow for flexibility. This combination allows the protocols to operate with less than full connectivity, to easily adapt to changes in group member-ship, and to make few assumptions about the underlying network topology. These features are all crucial to providing effective support for mobile and weakly-connected platforms. Deno has been implemented and runs on top of Linux and Windows NT/CE platforms. We use the Deno prototype to characterize the performance of two versions of Deno's protocol. The first ver-sion enables globally serializable execution of update transactions. The second supports a weaker consistency level that still guarantees transactionally consistent access to replicated data. The re-sults show that our protocols either outperform or perform comparably to existing approaches, while achieving higher availability. Further, we show that the incremental cost of providing global serializability in this environment is low. Finally, we show that commit delays can be sig-nificantly decreased by allowing votes to be cast, and votes and updates to be disseminated, speculatively. (Also cross-referenced as UMIACS-TR-99-70)