Optimistic Parallel State-Machine Replication

State-machine replication, a fundamental approach to fault tolerance, requires replicas to execute commands deterministically, which usually results in sequential execution of commands. Sequential execution limits performance and underuses servers, which are increasingly parallel (i.e., multicore). To narrow the gap between state-machine replication requirements and the characteristics of modern servers, researchers have recently come up with alternative execution models. This paper surveys existing approaches to parallel state-machine replication and proposes a novel optimistic protocol that inherits the scalable features of previous techniques. Using a replicated B+-tree service, we demonstrate in the paper that our protocol outperforms the most efficient techniques by a factor of 2.4 times

Rethinking State-Machine Replication for Parallelism

State-machine replication, a fundamental approach to designing fault-tolerant services, requires commands to be executed in the same order by all replicas. Moreover, command execution must be deterministic: each replica must produce the same output upon executing the same sequence of commands. These requirements usually result in single-threaded replicas, which hinders service performance. This paper introduces Parallel State-Machine Replication (P-SMR), a new approach to parallelism in state-machine replication. P-SMR scales better than previous proposals since no component plays a centralizing role in the execution of independent commands---those that can be executed concurrently, as defined by the service. The paper introduces P-SMR, describes a "commodified architecture" to implement it, and compares its performance to other proposals using a key-value store and a networked file system

High-performance state-machine replication

Replication, a common approach to protecting applications against failures, refers to maintaining several copies of a service on independent machines (replicas). Unlike a stand-alone service, a replicated service remains available to its clients despite the failure of some of its copies. Consistency among replicas is an immediate concern raised by replication. In effect, an important factor for providing the illusion of an uninterrupted service to clients is to preserve consistency among the multiple copies. State-machine replication is a popular replication technique that ensures consistency by ordering client requests and making all the replicas execute them deterministically and sequentially. The overhead of ordering the requests, and the sequentiality of request execution, the two essential requirements in realizing state-machine replication, are also the two major obstacles that prevent the performance of state-machine replication from scaling. In this thesis we concentrate on the performance of state-machine replication and enhance it by overcoming the two aforementioned bottlenecks, the overhead of ordering and the overhead of sequentially executing commands. To realize a truly scalable system, one must iteratively examine and analyze all the layers and components of a system and avoid or eliminate potential performance obstructions and congestion points. In this dissertation, we iterate between optimizing the ordering of requests and the strategies of replicas at request execution, in order to stretch the performance boundaries of state-machine replication. To eliminate the negative implications of the ordering layer on performance, we devise and implement several novel and highly efficient ordering protocols. Our proposals are based on practical observations we make after closely assessing and identifying the shortcomings of existing approaches. Communication is one of the most important components of any distributed system and thus selecting efficient communication patterns is a must in designing scalable systems. We base our protocols on the most suitable communication patterns and extend their design with additional features that altogether realize our protocol's high efficiency. The outcome of this phase is the design and implementation of the Ring Paxos family of protocols. According to our evaluations these protocols are highly scalable and efficient. We then assess the performance ramifications of sequential execution of requests on the replicas of state-machine replication. We use some known techniques such as state-partitioning and speculative execution, and thoroughly examine their advantages when combined with our ordering protocols. We then exploit the features of multicore hardware and propose our final solution as a parallelized form of state-machine replication, built on top of Ring Paxos protocols, that is capable of accomplishing significantly high performance. Given the popularity of state-machine replication in designing fault-tolerant systems, we hope this thesis provides useful and practical guidelines for the enhancement of the existing and the design of future fault-tolerant systems that share similar performance goals

Adoption of lean manufaturing system with AIM of efficiency improvement within a late lean adopter company (a case study)

“Lean manufacturing” (LM) and “Lean production” are the terms and concepts which have been introduced to industry world since 1990s. In these almost three decades many companies in various sectors have applied lean with aim of eliminating wastes and implementing continuous improvements in their organization. Although the capabilities and advantages of lean have been proven over the years, some companies are still hesitate to use this method. According to the theory of the “Diffusion of Innovation” (DOI), based on innovativeness factor, adopters to an innovation are divided into five categories: innovators, early adopters, early majority, late majority and laggards. Innovation can be considered as a new idea, procedure, practice, product and etc. Each of these categories has its own characteristics. The focus of this research is about adoption of LM in a laggard company. The case of this study (company X) is a furniture manufacturer in Quebec with mainly push production system. They are currently encountering with long delivery times, lack of space in the shop floor and unsatisfied production rate. Similar companies with the same problems as company X have improved their total efficiency with applying lean concept but our case has not been turned into LM until now and they are not very interested in implementing this procedure. Innovation-decision process has five stages: knowledge, persuasion, decision, implementation and confirmation. In this study, it is intended to help the company to reach to the third stage to make decision about lean implementation. Lean is a long and time taking journey and it will be longer in case of late adopters. The reason that they are reluctant in lean adoption is their ignorance about existing wastes and their impacts in the system. In such companies with traditional organizational structure, unawareness is the result of working in silos and having weak communications. In order to convince laggards to make decision about lean implementation, it is essential to break down the silos, improve interactions and deploy mutual synergy among them. Laggards will not accept an innovation until they completely become certain it is safe for them. In this research, we propose a road map to indicate the opportunity to increase total cycle efficiency from 29.4% to 78.3%

Effect of BA and Ovule Developmental Stages on Embryo Rescue in Perlette Grape (Vitis Vinifera L.) Cultivar

Production of seedless varieties is one of the major breeding goals in grape vine. Traditional methods result in low percentage of seedless progeny production. Today for producing high percentage of seedless progeny, embryo rescue are used. In this research, the effects of BA concentrations (0, 30, 60 and 100 mg L-1) and the stage of ovule development (25, 35, 45, 55 and 65 days after pollination) were assessed on the success rate of the embryo rescue in Perlette grape (Vitis vinifera L.). BA was sprayed 14 days before and 7days after the anthesis. The berries were harvested at 25, 35, 45, 55 and 65 days post pollination. Ovules were cultured  in Nitch and Nitch medium with 0.35 mg L-1gibberellic acid (GA3) and 1 mg L-1 indolacetic acid (IAA). Characters such as germination, collapsed, callus-formed and enlarged ovules were recorded. The results revealed the effect of BA pre-treating and ovule developmental stage on percentage of germinated embryos, collapsed, callus- formed and enlarged ovules. The highest germination percentage was observed in BA 100 mg L-1 at 65 days post pollination treatment. The highest percentage of the collapsed ovules was observed at 25 days after pollination in all treatments. The highest percentage of the callus formation was observed in the BA treatment of 30 mg L-1 at 55 days after pollination. The highest percentage of the enlarged ovules was observed in the BA treatment of 60 mg L-1 at 45 days after pollination

Bazı üzüm çeşitlerinde kış dinlenmesinin tesbiti üzerinde araştırmalar

Bu tezin, veri tabanı üzerinden yayınlanma izni bulunmamaktadır. Yayınlanma izni olmayan tezlerin basılı kopyalarına Üniversite kütüphaneniz aracılığıyla (TÜBESS üzerinden) erişebilirsiniz.ÖZET 1- Bu çalışma Kardinal, Yuvarlak Çekirdeksiz ve Jure Püskülü (Amerikan Üzümü) çeşitlerinde kış dinlenmesini incelemek amacıyla 1985-İ986 yıllarında E.Ü. Ziraat Fakültesi Bahçe Bit kileri Bölümünde yapılmıştır. 2- Araştırmada çevre koşullar