Update Consistency for Wait-free Concurrent Objects

In large scale systems such as the Internet, replicating data is an essential feature in order to provide availability and fault-tolerance. Attiya and Welch proved that using strong consistency criteria such as atomicity is costly as each operation may need an execution time linear with the latency of the communication network. Weaker consistency criteria like causal consistency and PRAM consistency do not ensure convergence. The different replicas are not guaranteed to converge towards a unique state. Eventual consistency guarantees that all replicas eventually converge when the participants stop updating. However, it fails to fully specify the semantics of the operations on shared objects and requires additional non-intuitive and error-prone distributed specification techniques. This paper introduces and formalizes a new consistency criterion, called update consistency, that requires the state of a replicated object to be consistent with a linearization of all the updates. In other words, whereas atomicity imposes a linearization of all of the operations, this criterion imposes this only on updates. Consequently some read operations may return out-dated values. Update consistency is stronger than eventual consistency, so we can replace eventually consistent objects with update consistent ones in any program. Finally, we prove that update consistency is universal, in the sense that any object can be implemented under this criterion in a distributed system where any number of nodes may crash.Comment: appears in International Parallel and Distributed Processing Symposium, May 2015, Hyderabad, Indi

Brief Announcement: Update Consistency in Partitionable Systems

Data replication is essential to ensure reliability, availability and fault-tolerance of massive distributed applications over large scale systems such as the Internet. However, these systems are prone to partitioning, which by Brewer's CAP theorem [1] makes it impossible to use a strong consistency criterion like atomicity. Eventual consistency [2] guaranties that all replicas eventually converge to a common state when the participants stop updating. However, it fails to fully specify shared objects and requires additional non-intuitive and error-prone distributed specification techniques, that must take into account all possible concurrent histories of updates to specify this common state [3]. This approach, that can lead to specifications as complicated as the implementations themselves, is limited by a more serious issue. The concurrent specification of objects uses the notion of concurrent events. In message-passing systems, two events are concurrent if they are enforced by different processes and each process enforced its event before it received the notification message from the other process. In other words, the notion of concurrency depends on the implementation of the object, not on its specification. Consequently, the final user may not know if two events are concurrent without explicitly tracking the messages exchanged by the processes. A specification should be independent of the system on which it is implemented. We believe that an object should be totally specified by two facets: its abstract data type, that characterizes its sequential executions, and a consistency criterion, that defines how it is supposed to behave in a distributed environment. Not only sequential specification helps repeal the problem of intention, it also allows to use the well studied and understood notions of languages and automata. This makes possible to apply all the tools developed for sequential systems, from their simple definition using structures and classes to the most advanced techniques like model checking and formal verification. Eventual consistency (EC) imposes no constraint on the convergent state, that very few depends on the sequential specification. For example, an implementation that ignores all the updates is eventually consistent, as all replicas converge to the initial state. We propose a new consistency criterion, update consistency (UC), in which the convergent state must be obtained by a total ordering of the updates, that contains the sequential order of eachComment: in DISC14 - 28th International Symposium on Distributed Computing, Oct 2014, Austin, United State

Causal Consistency: Beyond Memory

In distributed systems where strong consistency is costly when not impossible, causal consistency provides a valuable abstraction to represent program executions as partial orders. In addition to the sequential program order of each computing entity, causal order also contains the semantic links between the events that affect the shared objects -- messages emission and reception in a communication channel , reads and writes on a shared register. Usual approaches based on semantic links are very difficult to adapt to other data types such as queues or counters because they require a specific analysis of causal dependencies for each data type. This paper presents a new approach to define causal consistency for any abstract data type based on sequential specifications. It explores, formalizes and studies the differences between three variations of causal consistency and highlights them in the light of PRAM, eventual consistency and sequential consistency: weak causal consistency, that captures the notion of causality preservation when focusing on convergence ; causal convergence that mixes weak causal consistency and convergence; and causal consistency, that coincides with causal memory when applied to shared memory.Comment: 21st ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming, Mar 2016, Barcelone, Spai

Conformance relations for distributed testing based on CSP

Copyright @ 2011 Springer Berlin HeidelbergCSP is a well established process algebra that provides comprehensive theoretical and practical support for refinement-based design and verification of systems. Recently, a testing theory for CSP has also been presented. In this paper, we explore the problem of testing from a CSP specification when observations are made by a set of distributed testers. We build on previous work on input-output transition systems, but the use of CSP leads to significant differences, since some of its conformance (refinement) relations consider failures as well as traces. In addition, we allow events to be observed by more than one tester. We show how the CSP notions of refinement can be adapted to distributed testing. We consider two contexts: when the testers are entirely independent and when they can cooperate. Finally, we give some preliminary results on test-case generation and the use of coordination messages. © 2011 IFIP International Federation for Information Processing

Review of mycotoxin reduction in food and feed: from prevention in the field to detoxification by adsorption or transformation

Mycotoxins are secondary metabolites present worldwide in agricultural commodities and produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by animals. Prevention of mycotoxicoses includes pre- and post-harvest strategies. The best way to reduce the mycotoxin content in food and feed is the prevention of mycotoxin formation in the field, but this is often not sufficient, so other methods are needed. To decontaminate and/or detoxify mycotoxin-contaminated food and feed, the most prevalent approach in the feed industry is the inclusion of sorbent materials in the feed thus obtaining more or less selective removal of toxins by adsorption during passage through the gastrointestinal tract. Another reliable approach is to add enzymes or microorganisms capable of detoxifying some mycotoxins. Through a comprehensive review of published reports on the strategies for mycotoxin removal, this present work aims to update our understanding of mycotoxin removal. It provides an insight into the detoxification of mycotoxin present in food and feed. In the future, more emphasis needs to be placed on adsorption of mycotoxins in the gastrointestinal tract. Concerning the enzymatic transformation of mycotoxins, further efforts are required in understanding detoxification reactions, the toxicity of transformation products and in the characterization of enzymes responsible for transformations

Influence of Different Levels of Rosemary Leafs Powder Supplementation on Some Productive Traits of Broiler Chicken Ross Strain

أجري هذا البحث بإضافة مستويات مختلفة من مسحوق أوراق نبات إكليل الجبل الى العليقة بهدف دراسة تأثيرها في بعض الصفات الانتاجية لفروج اللحم سلالة روز. استخدم 300 فرخ لحم غير مجنس بعمر يوم واحد وقسمت بالتساوي الى خمسة معاملات تجريبية بواقع مكررين لكل معاملة 30) فرخ لكل مكرر), غذيت الافراخ على عليقة بادئ من عمر يوم واحد الى نهاية الاسبوع الثالث بعدها استبدلت بعليقة نهائية من بداية الاسبوع الرابع الى نهاية الاسبوع السادس, اضيف للعليقتين أربع نسب من مسحوق أوراق نبات أكليل الجبل وهي ,0 ,0.5 ,1 ,1.5 2% والتي مثلت المعاملات التجريبية. أظهرت النتائج تفوقا معنويا على مستوى ((P≤0.05 في معدلات وزن الجسم الحي والزيادة الوزنية التراكمية وكفاءة التحويل الغذائي والنسبة المئوية للتصافي عند عمر 3 و6 اسابيع لطيور المعاملات التي غذيت على مسحوق أوراق نبات أكليل الجبل في علائقها مقارنة مع معاملة السيطرة. علاوة على أن نسبة الهلاكات الكلية انخفضت بشكل معنوي (P≤0.05) للمعاملات المضاف لها مسحوق أوراق نبات إكليل الجبل مقارنة مع معاملة السيطرة. The research was conducted to investigate the effect of different levels of rosemary powder supplementation  on some productive traits of broiler chicken ross strain. Three hundred unsexed broiler chicks of one-day-old were equally divided into five groups, 2 replicates per group (30 chicks per replicate). Chicks were fed on starter diet from one-day-old until end of three weeks then replaced to finisher diet from the beginning of four weeks until the end of six weeks, starter and finisher diet supplemented with four ratios from rosemary powder 0, 0.5, 1, 1.5 and 2% which represented experimental groups.                                                        Results showed a significant superiority (P≤0.05) in average live body weight, weight gain, feed conversion ratio and dressing percentage in birds supplemented with rosemary powder as compared with control group at 3 and 6 weeks of birds age. Moreover, supplementation of rosemary had significantly (P≤0.05) decreased mortality ratio in experimental groups as compared with the control group.                                            It can be concluded that supplementation of rosemary powder to the diet had a profound effect to enhance productive traits of broiler chicken ross strain

Back in Time Petri Nets

11th Int. Conf. on Formal Modeling and Analysis of Timed Systems (FORMATS'13) July 2013 Buenos AiresInternational audienceThe time progress assumption is at the core of the semantics of real-time formalisms. It is also the major obstacle to the development of partial-order techniques for real-time distributed systems since the events are ordered both by causality and by their occurrence in time. Anyway, extended free choice safe time Petri nets (TPNs) were already identi ed as a class where partial order semantics behaves well. We show that, for this class, the time progress assumption can even be dropped (time may go back in case of concurrency), which establishes a nice relation between partial-order semantics and time progress assumption