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Self-adaptive user profiles for large-scale data delivery

Push based data delivery requires knowledge of user interests for making scheduling, bandwidth allocation, and routing decisions. Such information is maintained as user profiles. We propose a novel incremental algorithm for constructing user profiles based on monitoring and user feedback. In contrast to earlier approaches, which typically represent profiles as a single weighted interest vector, we represent user profiles as multiple interest vectors, whose number, size, and elements change adaptively based on user access behavior. This flexible approach allows the profile to more accurately represent complex user interests. Although there has been significant research on user profiles, our approach is unique in that it can be tuned to trade-off profile complexity and quality. This feature, together with its incremental nature, makes our method suitable for use in large scale information filtering applications such as push based WWW page dissemination. We evaluate the method by experimentally investigating its ability to categorize WWW pages taken from Yahoo! categories. Our results show that the method can provide high filtering effectiveness with modest profile sizes and can effectively adapt to changes in users interests.

Support for speculative update propagation and mobility in Deno

This paper presents the replication framework of Deno, an object replication system specifically designed for 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 membership, and to make few assumptions about the underlying network topology. Deno has been implemented and runs on top of Linux and Win32 platforms. We use the Deno prototype to characterize the performance of two versions of Denos protocol. The first version enables globally serializable execution of update transactions. The second supports a weaker consistency level that still guarantees transactionally-consistent access to replicated data. We demonstrate that the incremental cost of providing global serializability is low, and that speculative dissemination of updates can significantly improve commit performance.

Consistency management in Deno

We describe a new replicated‐object protocol designed for use in mobile and weakly‐connected environments. The protocol differs from previous protocols in combining epidemic information propagation with voting, and in using fixed per‐object currencies for voting. The advantage of epidemic protocols is that data movement only requires pair‐wise communication. Hence, there is no need for a majority quorum to be available and simultaneously connected at any single time. The protocols increase availability by using voting, rather than primary‐copy or primary‐commit schemes. Finally, the use of per‐object currencies allows voting to take place in an entirely decentralized fashion, without any server having complete knowledge of group membership. We show that currency allocation can be used to implement diverse policies. For example, uniform currency distributions emulate traditional voting schemes, while allocating all currency to a single server emulates a primary‐copy scheme. We present simulation results showing both schemes, as well as the performance advantages of using currency proxies to temporarily reallocate currency during planned disconnections. Furthermore, we discuss an initial design of the underlying replicated‐object system and present a basic API.

Light-weight currency management mechanisms in Deno

Discusses the currency management mechanisms used in Deno, a replicated-object storage system designed for use in mobile and weakly-connected environments. Deno primarily differs from previous work in implementing an asynchronous weighted-voting scheme via epidemic information flow, and in committing updates in an entirely decentralized fashion, without requiring any server to have complete knowledge of system membership. We first give an overview of Deno, briefly discussing its voting scheme, proxy mechanism, basic API and commit performance. We then present currency management mechanisms, based on peer-to-peer currency exchanges, that enable lightweight replica creation, retirement and currency redistribution while maintaining protocol correctness. We also demonstrate that peer-to-peer currency exchanges can be used to exponentially converge to arbitrary target currency distributions.

Light-Weight Currency Management Mechanisms in Mobile and Weakly-Connected Environments

This paper discusses the currency management mechanisms used in Deno, an object replication system designed for use in mobile and weakly-connected environments. Deno primarily differs from previous work in implementing an asynchronous weighted-voting scheme via epidemic information flow, and in committing updates in an entirely decentralized fashion, without requiring any server to have complete knowledge of system membership.We first give an overview of Deno, discussing its voting scheme, proxy mechanism, basic API, and commit performance. We then focus on the issue of currency management. Although there has been much work on currency management in synchronous, strongly-connected environments, this issue has not been explored in asynchronous, weakly-connected environments. We present currency management mechanisms, based on peer-to-peer currency exchanges, that enable light-weight replica creation, retirement, and currency redistribution while maintaining the correctness of the underlying consistency protocol. We also demonstrate that peer-to-peer currency exchanges can be used to exponentially converge to arbitrary target currency distributions, without the need for any server to have global system information.

Design and evaluation of redistribution strategies for wide-area commodity distribution

The proliferation of e-commerce has enabled a new set of applications that allow globally distributed purchasing of commodities such as books, CDs, travel tickets, etc., over the Internet. These commodities can be represented online by tokens, which can be distributed among servers to enhance the performance and availability of such applications. There are two fundamental approaches for distributing such tokens-partitioning and replication. Partitioning-based approaches eliminate the need for tight quorum synchronization required by replication-based approaches. The effectiveness of partitioning, however, relies on token redistribution techniques that allow dynamic migration of tokens to where they are needed. We propose pair-wise token redistribution strategies to support applications that involve wide-area commodity distribution. Using a detailed simulation model and real Internet message traces, we investigate the performance of our redistribution strategies and a previously proposed replication based scheme. Our results reveal that, for the types of applications and environment we address, partitioning-based approaches perform superior primarily due to their ability to provide higher server autonomy.

Research in Data Broadcast and Dissemination

The proliferation of the Internet and intranets, the development of wireless and satellite networks, and the availability of asymmetric, high-bandwidth links to the home, have fueled the development of a wide range of new “dissemination-based” applications. These applications involve the timely distribution of data to a large set of consumers, and include stock and sports tickers, traffic information systems, electronic personalized newspapers, and entertainment delivery. Dissemination-oriented applications have special characteristics that render traditional client-server data management approaches ineffective. These include: n n ntremendous scale. n n na high-degree of overlap in user data needs. n n nasymmetric data flow from sources to consumers.

Performance of mobile, single-object, replication protocols

Discusses the implementation and performance of bounded voting, which is a new object replication protocol designed for use in mobile and weakly-connected environments. We show that the protocol eliminates several restrictions of previous work, such as the need for (1) strong or complete connectivity, (2) complete knowledge of system membership, and (3) low update rates. The protocol implements an asynchronous, weighted-voting scheme via epidemic information flow, and commits updates in an entirely decentralized fashion. A proxy mechanism is used to enable transparent handling of planned disconnections. We use a detailed simulation study to characterize the performance of bounded voting under a variety of loads and environments, and to compare it to another decentralized epidemic protocol. We further investigate the performance impact of the proxy mechanism.