Effect of transaction start time interval on the performance of optimistic concurrency control scheme in mobile environment

Author(s):  
Sirajo Abdullahi Bakura ◽  
Aminu Mohammed

Large in-memory data structures have a significant application in the fields of graphics, gaming, military and all the possible areas where Big Data can be employed. Their fame in the area of science and technology is attributable to fast in-memory access by the processor as compared to on-disk data structures. These enormous data structures can be accessed still fast and efficiently through parallel computing. For employing highly parallel computations, equally parallel algorithms are required. One of the most desirable attributes of such algorithms is their ability to control concurrency and avoid any deadlocks while being time and energy efficient. This paper presents a multi-version optimistic concurrency control algorithm based on timestamping. This algorithm is lock free and is tested on 64 simulated CPU cores on a multi core simulator. The algorithm is a Software Transactional Memory approach employing 16, 32, 40 and 50 threads in different tests running on the simulator. Half of the threads are doing reading and half are doing writing operation in each case while accessing an in-memory dynamic array. Being lock free and employing lazy timestamp calculations, this approach is better than other existing concurrency control approaches.


2020 ◽  
Vol 20 (3) ◽  
pp. 71-78
Author(s):  
Yong-Hyeog Kang ◽  
◽  
Wonhyung Park

Author(s):  
Adnan Mujanovic ◽  
Christoph Kammer ◽  
Christoph C Kurmann ◽  
Lorenz Grunder ◽  
Morin Beyeler ◽  
...  

Introduction : The value of intravenous thrombolysis (IVT) in patients eligible for mechanical thrombectomy (MT) remains unclear. We hypothesized that pre‐treatment with and/or ongoing IVT may facilitate reperfusion of distal vessel occlusion after incomplete MT. We evaluated this potential association using follow‐up perfusion imaging. Methods : Retrospective observational analysis of our institution`s stroke registry included patients with incomplete reperfusion after MT, admitted between February 1, 2015 and December 8, 2020. Delayed reperfusion (DR) was defined as the absence of a persistent perfusion deficit on contrast‐enhanced perfusion imaging ⁓24h±12h after the intervention. The association between baseline parameters and the occurrence of DR was evaluated using a logistic regression analyses. To account for possible time‐dependent associations of IVT with DR, additional stratification sets were made based on different time windows between IVT start time and final angiography runs. Results : Among the 378 included patients (median age 73.5, 50.8% female), DR occurred in 226 (59.8%). Atrial fibrillation (aOR 2.53 [95% CI 1.34 ‐ 4.90]), eTICI score (aOR 3.79 [95% CI 2.71 ‐ 5.48] per TICI grade increase), and intervention‐to‐follow‐up time (aOR 1.08 [95% CI 1.04 ‐ 1.13] per hour delay) were associated with DR. Dichotomized IVT strata showed no association with DR (aOR 0.75 [95% CI 0.42 ‐ 1.33]), whereas shorter intervals between IVT start and end of the procedure showed a borderline significant association with DR (OR 2.24 [95% CI 0.98 ‐ 5.43, and OR 2.07 [95% 1.06 – 4.31], for 80 and 100 minutes respectively). Patients with DR had higher rates of functional independence (modified Rankin scale 0–2 at 90 days, DR: 63.3% vs PPD: 38.8%; p<0.01) and longer survival time (at 3 years, DR: 69.2% vs PPD: 45.8%; p = 0.001). Conclusions : There is weak evidence that IVT may favor DR after incomplete MT if the time interval between IVT administration and end of the procedure is short. In general, perfusion follow‐up imaging may constitute a suitable surrogate parameter for evaluating medical rescue strategies after incomplete MT, because a considerable proportion of patients do not experience DR, and there seems to be a close correlation with clinical outcomes.


Author(s):  
С.А. Олейникова ◽  
И.А. Селищев

Статья посвящена разработке имитационной модели, позволяющей оценить вероятностно-временные показатели случайной величины, представляющей собой длительность выполнения комплекса последовательно-параллельных работ. В первую очередь, к таким показателям относятся закон распределения случайной величины (с точностью до параметров), вероятность завершения проекта в некотором временном интервале, а также математическое ожидание и дисперсия. Потребность в решении поставленной задачи возникает в случае, если длительности отдельных работ являются случайными величинами. В этом случае временные характеристики завершения комплекса работ необходимы не только для оценки вероятностно-временных характеристик, но и для простейшего планирования времени начала каждой из работ. В настоящее время существуют подходы к решению данной задачи, наиболее распространенным из которых является PERT (Program Evaluation and Review Technique, техника оценки и анализа проектов). Однако оценки метода базируются на центральной предельной теореме, основывающейся на предположениях, которые в условиях реального функционирования производственных или обслуживающих систем невыполнимы. В силу этого возникает необходимость в получении модели, позволяющей оценить требуемые характеристики в любых условиях. В результате получена имитационная модель, позволяющая получить вероятностно-временные характеристики случайной величины, представляющей собой длительность комплекса последовательно-параллельных работ и отличающейся повышенной точностью по сравнению с существующими аналогами. Для реализации модели выбрана среда AnyLogic The article is devoted to the development of a simulation model that allows you to estimate the probabilistic-time indicators of a random variable, which is the duration of the completion of the complex of sequential-parallel works. First of all, such indicators include: the law of the distribution of a random value (with an accuracy of parameters), the probability of completing the project in some time interval, as well as a mathematical expectation and dispersion. The need for solving the task arises in the case if the duration of individual works are random values. In this case, the time characteristics of the completion of the work complex are necessary not only to assess the probabilistic-time characteristics but also for the simplest planning of the start time of each work. Currently, there are approaches to solving this task, the most common of which is PERT (Program Evaluation and Review Technique, an evaluation and project analysis technique). However, the estimates of the method are based on the central limit theorem based on assumptions that are impracticable in the real functioning of industrial or serving systems. Because of this, it is necessary to obtain a model that allows one to estimate the required characteristics in any conditions. As a result, a simulation model was obtained, which allows one to obtain the probabilistic-time characteristics of a random variable, which is the duration of a complex of sequential-parallel works and characterized by increased accuracy compared to existing analogues. For the implementation of the model, we chose AnyLogic medium


Sign in / Sign up

Export Citation Format

Share Document