Deterministic Object Management in Large Distributed Systems

Caching is a widely used technique to improve the scalability of distributed systems. A central issue with caching is maintaining object replicas consistent with their master copies. Large distributed systems, such as the Web, typically deploy heuristic-based consistency mechanisms, which increase delay and place extra load on the servers, while not providing guarantees that cached copies served to clients are up-to-date. Server-driven invalidation has been proposed as an approach to strong cache consistency, but it requires servers to keep track of which objects are cached by which clients. We propose an alternative approach to strong cache consistency, called MONARCH, which does not require servers to maintain per-client state. Our approach builds on a few key observations. Large and popular sites, which attract the majority of the traffic, construct their pages from distinct components with various characteristics. Components may have different content types, change characteristics, and semantics. These components are merged together to produce a monolithic page, and the information about their uniqueness is lost. In our view, pages should serve as containers holding distinct objects with heterogeneous type and change characteristics while preserving the boundaries between these objects. Servers compile object characteristics and information about relationships between containers and embedded objects into explicit object management commands. Servers piggyback these commands onto existing request/response traffic so that client caches can use these commands to make object management decisions. The use of explicit content control commands is a deterministic, rather than heuristic, object management mechanism that gives content providers more control over their content. The deterministic object management with strong cache consistency offered by MONARCH allows content providers to make more of their content cacheable. Furthermore, MONARCH enables content providers to expose internal structure of their pages to clients. We evaluated MONARCH using simulations with content collected from real Web sites. The results show that MONARCH provides strong cache consistency for all objects, even for unpredictably changing ones, and incurs smaller byte and message overhead than heuristic policies. The results also show that as the request arrival rate or the number of clients increases, the amount of server state maintained by MONARCH remains the same while the amount of server state incurred by server invalidation mechanisms grows

Benchmarking Hashing Algorithms for Load Balancing in a Distributed Database Environment

Modern high load applications store data using multiple database instances. Such an architecture requires data consistency, and it is important to ensure even distribution of data among nodes. Load balancing is used to achieve these goals. Hashing is the backbone of virtually all load balancing systems. Since the introduction of classic Consistent Hashing, many algorithms have been devised for this purpose. One of the purposes of the load balancer is to ensure storage cluster scalability. It is crucial for the performance of the whole system to transfer as few data records as possible during node addition or removal. The load balancer hashing algorithm has the greatest impact on this process. In this paper we experimentally evaluate several hashing algorithms used for load balancing, conducting both simulated and real system experiments. To evaluate algorithm performance, we have developed a benchmark suite based on Unidata MDM~ -- a scalable toolkit for various Master Data Management (MDM) applications. For assessment, we have employed three criteria~ -- uniformity of the produced distribution, the number of moved records, and computation speed. Following the results of our experiments, we have created a table, in which each algorithm is given an assessment according to the abovementioned criteria

Review of Julia Lavid-López, Carmen Maíz-Arévalo and Juan Rafael Zamorano-Mansilla.2021. Corpora in Translation and Contrastive Research in the Digital Era.

publishedVersionNon peer reviewe

Mind the source data! : Translation equivalents and translation stimuli from parallel corpora

Statements like ‘Word X of language A is translated with word Y of language B’ are incorrect, although they are quite common: words cannot be translated, as translation takes place on the level of sentences or higher. A better term for the correspondence between lexical items of source texts and their matches in target texts would be translation equivalence (Teq). In addition to Teq, there exists a reverse relation—translation stimulation (Tst), which is a correspondence between the lexical items of target texts and their matches (=stimuli) in source texts. Translation equivalents and translation stimuli must be studied separately and based on natural direct translations. It is not advisable to use pseudo-parallel texts, i.e. aligned pairs of translations from a ‘hub’ language, because such data do not reflect real translation processes. Both Teq and Tst are lexical functions, and they are not applicable to function words like prepositions, conjunctions, or particles, although it is technically possible to find Teq and Tst candidates for such words as well. The process of choosing function words when translating does not proceed in the same way as choosing lexical units: first, a relevant construction is chosen, and next, it is filled with relevant function words. In this chapter, the difference between Teq and Tst will be shown in examples from Russian–Finnish and Finnish–Russian parallel corpora. The use of Teq and Tst for translation studies and contrastive semantic research will be discussed, along with the importance of paying attention to the nature of the texts when analysing corpus findings.acceptedVersionPeer reviewe

Corpus-Based Analysis of Russian Translations of Animal Farm by George Orwell

The phenomenon of multiple translations of same classical works has been discussed extensively since 18th century. The dominant approach however is to study retranslating as a cultural, not a linguistic phenomenon. For unknown reasons, little use has been made of corpus data in research on this topic, although corpora of retranslated texts would seem to be a natural source of empirical data. Studying multiple translations with the help of corpus-based methods makes it possible to obtain the general picture of the data and to find its critical points. The quantitative data can be used for developing criteria for evaluation of the texts. In this paper, six Russian translations of George Orwell's Animal Farm are studied. The translations are compared against an unedited machine translation. A multidimensional scaling of the frequency-list-based distance matrix was performed. The analysis demonstrated that the most frequently republished translations are the most distant from the MT. The keyword analysis of the translations confirmed the findings of the MDS analysis and gave concrete clues on the lexical items typical for certain translations.acceptedVersionPeer reviewe

The Walker Function

The special function (the Walker function) and its derivatives are important for the description of near-wall turbulent flows. This article gives exact expressions for these functions, based on original identities for the hypergeometric functions 1F1 and pFp . We also introduce a new initial value problem that generates interpolating functions for (the Walker function) and its derivatives.Indisponível

Feasible domain of Walker's unsteady wall-layer model for the velocity profile in turbulent flows

The present work studies, in detail, the unsteady wall-layer model of Walker et al. (1989, AIAA J., 27, 140 – 149) for the velocity profile in turbulent flows. Two new terms are included in the transcendental non-linear system of equations that is used to determine the three main model parameters. The mathematical and physical feasible domains of the model are determined as a function of the non-dimensional pressure gradient parameter (p+). An explicit parameterization is presented for the average period between bursts (T+B), the origin of time (t+0) and the integration constant of the time dependent equation (A0) in terms of p+. In the present procedure, all working systems of differential equations are transformed, resulting in a very fast computational procedure that can be used to develop real-time flow simulators.O presente trabalho estuda em detalhe o modelo parietal transiente de Walker et al. (1989, AIAA J., 27, 140-149) para perfis de velocidade em escoamentos turbulentos. Dois novos termos são adicionados ao sistema transcendental não linear de equações que é utilizado para determinar os três principais parâmetros do modelo. Os domínios matemático e físico de validade do modelo são determinados como uma função do parâmetro gradiente de pressão adimensional (p+). Uma parametrização explícita em termos de p+ é apresentada para o período médio entre eventos (T+B), para a origem do tempo (t+0) e para a constante de integração (A0) da equação dependente do tempo. Na presente análise, todos os sistemas de equações diferenciais são transformados, resultando em um procedimento computacional rápido que pode ser utilizado para o desenvolvimento de simuladores em tempo real

The drag coefficient of a sphere: An approximation using Shanks transform

An accurate model for the drag coefficient (CD) of a falling sphere is presented in terms of a non-linear rational fractional transform of the series of Goldstein (Proc. Roy. Soc. London A, 123, 225-235, 1929) to Oseen's equation. The coefficients of the six polynomial terms are improved through a direct fit to the experimental data of Roos and Willmarth (AIAA J., 9:285-290, 1971). The model predicts CD up to Reynolds number 100,000 with a standard deviation of 0.04. Results are compared with eight different formulations of other authors.Indisponível