1,720,976 research outputs found
Asynchrony versus bulk-synchrony for a generalized N-body problem from genomics
No full textThis work examines a data-intensive irregular application from genomics, a long-read to long-read alignment problem, which represents a kind of Generalized N-Body problem, one of the "seven giants"of the NRC Big Data motifs [5]. In this problem, computations (genomic alignments) are performed on sparse and data-dependent pairs of inputs, with variable cost computation and variable datum sizes. In particular, there is no inherent locality in the pairwise interactions, unlike simulation-based N-Body problems, and the interaction sparsity depends on particular parameters of the input, which can also affect the quality of the output. We examine two extremes to distributed memory parallelization for this problem, bulk-synchrony and asynchrony, with real workloads. Our bulk-synchronous implementation, uses collective communication in MPI, while our asynchronous implementation uses cross-node RPCs in UPC++. We show that the asynchronous version effectively hides communication costs, with a memory footprint that is typically much lower than the bulk-synchronous version. Our application, while simple enough to be a kind of proxy for genomics or data analytics applications more broadly, is also part of a real application pipeline. It shows good scaling on real input problems, and at the same time, reveals some of the programming and architectural challenges for scaling this type of data-intensive irregular application
Memory Management for Lock-Free Data-Structures
No full textLock-free data structures achieve high responsiveness, aid scalability, and avoid deadlocks and livelocks. But providing memory management support for such data structures without foiling their progress guarantees is difficult. Often, designers employ the hazard pointers technique, which may imposes a high performance overhead. In this talk we present the optimistic access scheme that provides efficient reclamation support for lock-free data-structures and also some automatization.Non UBCUnreviewedAuthor affiliation: TechnionFacult
Limitations of Partial Compaction: Towards Practical Bounds
No full textCompaction of a managed heap is a costly operation to be avoided as much as possible in commercial runtimes. Instead, partial compaction is often used to defragment parts of the heap and avoid space blowup. Previous study of compaction limitation provided some initial asymptotic bounds but no implications for practical systems. In this work, we extend the theory to obtain better bounds and make them strong enough to become meaningful for modern systems.IINFCO
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lower and upper bounds on obtaining history independence
No full textAbstractHistory independent data structures, presented by Micciancio, are data structures that possess a strong security property: even if an intruder manages to get a copy of the data structure, the memory layout of the structure yields no additional information on the history of operations applied on the structure beyond the information obtainable from the content itself. Naor and Teague proposed a stronger notion of history independence in which the intruder may break into the system several times without being noticed and still obtain no additional information from reading the memory layout of the data structure. An open question posed by Naor and Teague is whether these two notions are equally hard to obtain. In this paper we provide a separation between the two requirements for comparison-based algorithms. We show very strong lower bounds for obtaining the stronger notion of history independence for a large class of data structures, including, for example, the heap and the queue abstract data structures. We also provide complementary upper bounds showing that the heap abstract data structure may be made weakly history independent in the comparison based model without incurring any additional (asymptotic) cost on any of its operations. (A similar result is easy for the queue.) Thus, we obtain the first separation between the two notions of history independence. The gap we obtain is exponential: some operations may be executed in logarithmic time (or even in constant time) with the weaker definition, but require linear time with the stronger definition
Concurrent aggregate queries
Get PDFConcurrent data structures serve as fundamental building blocks for
concurrent computing. Many concurrent counterparts have been designed for basic
sequential mechanisms; however, one notable omission is a concurrent tree that
supports aggregate queries. Aggregate queries essentially compile succinct
information about a range of data items, for example, calculating the average
salary of employees in their 30s. Such queries play an essential role in
various applications and are commonly taught in undergraduate data structures
courses. In this paper, we formalize a type of aggregate queries that can be
efficiently supported by concurrent trees and present a design for implementing
these queries on concurrent trees. We bring two algorithms implementing this
design, where one optimizes for tree update time, while the other optimizes for
aggregate query time. We analyze their correctness and complexity,
demonstrating the trade-offs between query time and update time
Brief Announcement: Concurrent Aggregate Queries
Get PDFConcurrent data structures serve as fundamental building blocks for concurrent computing. Many concurrent counterparts have been designed for basic sequential algorithms; however, one notable omission is a concurrent tree that supports aggregate queries. Aggregate queries essentially compile succinct information about a range of data items. Such queries play an essential role in various applications and are commonly taught in undergraduate data structures courses. In this paper, we formalize a type of aggregate queries that can be efficiently supported by concurrent trees and present a design for implementing these queries on concurrent lock-based trees. We present two algorithms implementing this design, where one optimizes for tree update time, while the other optimizes for aggregate query time
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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