Transactional memory (TM) systems have gained considerable popularity in the last decade driven by the increased demand for tools that ease parallel programming. TM eliminates the need for user-locks that protect accesses to shared data. It offers performance close to that of fine-grain locking with the programming simplicity of coarse-grain locking. Today’s TM systems implement the two-phase-locking (2PL) algorithm which aborts transactions every time a conflict occurs. 2PL is a simple algorithm that provides fast transactional operations. However, it limits concurrency in applications with high contention because it increases the rate of aborts. We propose the use of a more relaxed concurrency control algorithm to provide better concurrency. This algorithm is based on the conflict-serializability (CS) model. Unlike 2PL, it allows some transactions to commit successfully even when they make conflicting accesses. We implement this algorithm both in a software TM system as well as in a simulator of a hardware TM system. Our evaluation using TM benchmarks shows that the algorithm improves the performance of applications with long transactions and high abort rates. Performance is improved by up to 299% in the software TM, and up to 66% in the hardware simulator. We argue that these improvements come with little additional complexity and require no changes to the transactional programming model. This makes our implementation feasible

MOREIRA, Leonardo Oliveira. DTX: um mecanismo de controle de concorrência distribuído para dados XML. 2008. 89 f. Dissertação (Mestrado em ciência da computação)- Universidade Federal do Ceará, Fortaleza-CE, 2008. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-11T17:50:32Z No. of bitstreams: 1 2008_dis_lomoreira.pdf: 5597130 bytes, checksum: 9a74d13a49d1367fd13d8ff4c140fdc4 (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2016-07-18T16:01:30Z (GMT) No. of bitstreams: 1 2008_dis_lomoreira.pdf: 5597130 bytes, checksum: 9a74d13a49d1367fd13d8ff4c140fdc4 (MD5) / Made available in DSpace on 2016-07-18T16:01:30Z (GMT). No. of bitstreams: 1 2008_dis_lomoreira.pdf: 5597130 bytes, checksum: 9a74d13a49d1367fd13d8ff4c140fdc4 (MD5) Previous issue date: 2008 / XML has become a widely used standard for data representation and exchange among Web applications. Consequently, a large volume of such data is distributed all over the Web and stored using several persistence methods. DBMSs provide concurrency control techniques to manage data. However, the structure of XML data makes it difficult to use these techniques. Projects are being proposed and they provide management of XML documents. Nevertheless, most of these projects do not provide efficient concurrency control mechanisms for distributed data. Some of them do provide support for distributed control of XML data, but use protocols that have limitations and offer low concurrency levels. In order to provide effective data management in distributed environments, we present DTX, a distributed concurrency control mechanism for XML data that takes into account its structural characteristics. DTX aims to provide effective management of XML data and contemplate properties such as isolation and consistency in transactions, using a multi-granular concurrency control protocol that increases parallelism among transactions and that has an optimized structure for data representation. DTX has a modular and flexible architecture, allowing for easy integration with any XML storage mechanisms. Moreover, DTX can be extended by adding new features to it. In order to evaluate DTX, several experiments were conducted comparing DTX as it is with a variation of DTX that uses a fine-grained protocol, in an attempt to simulate existing strategies in related work. Results confirm DTX’s effectiveness considering different aspects of distributed transactions on XML data, improving their performance, i.e., transaction execution time. / XML tornou-se um padrão amplamente utilizado na representação e troca de dados entre aplicações na Web. Com isso, grande volume desses dados está distribuído na Web e armazenado em diversos meios de persistência. SGBD relacionais que suportam XML fornecem técnicas de controle de concorrência para gerenciar esses dados. A estrutura dos dados XML, entretanto, dificulta a aplicação dessas técnicas. Trabalhos estão sendo propostos e fornecem gerenciamento de documentos XML. A maioria destes trabalhos, todavia, não oferecem um controle de concorrência eficiente para dados distribuídos. Outros trabalhos dão suporte ao controle distribuído de dados XML, mas estes possuem protocolos com baixo grau de concorrência e limitações. Para prover um gerenciamento eficaz em ambientes distribuídos, este trabalho apresenta o DTX, como mecanismo para o controle de concorrência distribuído para dados XML, que leva em consideração características estruturais destes dados. O DTX visa a um gerenciamento eficaz de dados XML e contemplar as propriedades de isolamento e consistência em transações, utilizando um protocolo para controle de concorrência multigranular que aumenta o paralelismo entre as transações e possui uma estrutura otimizada para representação dos dados. A solução proposta possui uma arquitetura modular e flexível, o que facilita sua integração com diferentes estruturas de armazenamento XML, além de poder ser estendido, adicionando novos recursos. Para validar o DTX, diversos testes foram feitos, comparando o DTX descrito neste trabalho com uma variação do DTX, utilizando um protocolo de maior granulosidade, visando a simular as estratégias dos trabalhos relacionados. Os resultados obtidos atestam a eficácia do DTX, considerando diferentes aspectos em transações distribuídas a dados XML, melhorando o desempenho, ou seja, o tempo de execução destas transações.

Headlong Developments' application HeadmasterDev is currently adapted for a single user. To turn their application into a multi-user system the programming language Swift will be used. Furthermore, this thesis will evaluate whether Swift is an appropriate programming language for developing a server application, how to handle concurrency of shared resources and if it is possible to deploy the application on a operative system other than macOS. The result is that the concurrency model is dependent on the system's needs and that one should not commit to using Swift as the programming language for a server application, with some regard to the size of the application and it's uses. / Headlong Developments applikation HeadmasterDev är endast anpassad för en användare. För att kunna transformera deras applikation till ett fleranvändarsystem så kommer detta arbete att använda sig av programmeringsspråket Swift. Utöver detta kommer det även undersökas om programmeringsspråket Swift är lämpligt för denna typ av applikation, hur man bäst hanterar samtidighet av delade resurser och om det är möjligt att använda applikationen på en annan plattform än macOS. Resultatet kom att bli att hur man löser samtidighetsproblemen beror på systemets behov och att Swift inte är lämpligt för denna applikation med tanke på dess storlek och användningsområden.

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<p>The goal of this dissertation is to design a collection of techniques and tools that enable<br> the ease of programming under the traditional strong concurrency guarantees, without sacrificing the performance offered by modern distributed database systems. Our main thesis<br> is that language-centric reasoning can help developers efficiently identify and eliminate con-<br> currency anomalies in modern database programs, and we have demonstrated that it results<br> in faster and safer database programs</p>

La collaboration en temps réel est un cas spécial de collaboration où les utilisateurs travaillent sur le même élément simultanément et sont au courant des modifications des autres utilisateurs en temps réel. Les données distribuées doivent rester disponibles et consistant tout en étant répartis sur plusieurs systèmes physiques. "Strong Consistency" est une approche qui crée un ordre total des opérations en utilisant des mécanismes tel que le "locking". Cependant, cela introduit un "bottleneck". Ces dix dernières années, les algorithmes de concurrence ont été étudiés dans le but de garder la convergence de tous les replicas sans utiliser de "locking" ni de synchronisation. "Operational Trans- formation" et "Conflict-free Replicated Data Types (CRDT)" sont utilisés dans ce but. Cependant, la complexité de ces stratégies les rend compliquées à intégrer dans des logicielles conséquents, comme les éditeurs de modèles, spécialement pour des data structures complexes comme les graphes. Les implémentations actuelles intègrent seulement des data linéaires tel que le texte. Dans ce mémoire, nous présentons CollabServer, un framework pour construire des environnements de collaboration. Il a une implémentation de CRDTs pour des data structures complexes tel que les graphes et donne la possibilité de construire ses propres data structures. / Real-time collaboration is a special case of collaboration where users work on the same artefact simultaneously and are aware of each other’s changes in real-time. Shared data should remain available and consistent while dealing with its physically distributed aspect. Strong Consistency is one approach that enforces a total order of operations using mechanisms, such as locking. This however introduces a bottleneck. In the last decade, algorithms for concurrency control have been studied to keep convergence of all replicas without locking or synchronization. Operational Transformation and Conflict free Replicated Data Types (CRDT) are widely used to achieve this purpose. However, the complexity of these strategies makes it hard to integrate in large software, such as modeling editors, especially for complex data types like graphs. Current implementations only integrate linear data, such as text. In this thesis, we present CollabServer, a framework to build collaborative environments. It features a CRDTs implementation for complex data types such as graphs and gives possibility to build other data structures.

Data warehouses (DWs) have traditionally been loaded with data at regular time intervals, e.g., monthly, weekly, or daily, using fast bulk loading techniques. Recently, the trend is to insert all (or only some) new source data very quickly into DWs, called near-realtime DWs (right-time DWs). This is done using regular INSERT statements, resulting in too low insert speeds. There is thus a great need for a solution that makes inserted data available quickly, while still providing bulk-load insert speeds. This paper presents RiTE ('Right-Time ETL'), a middleware system that provides exactly that. A data producer (ETL) can insert data that becomes available to data consumers on demand. RiTE includes an innovative main-memory based catalyst that provides fast storage and offers concurrency control. A number of policies controlling the bulk movement of data based on user requirements for persistency, availability, freshness, etc. are supported. The system works transparently to both producer and consumers. The system is integrated with an open source DBMS, and experiments show that it provides 'the best of both worlds', i.e., INSERT-like data availability, but with bulk-load speeds (up to 10 times faster).

O uso de Web Services tem aberto novas possibilidades de desenvolvimento de software, entre elas a composição de serviços. A composição de serviços apresenta novas questões no ambiente computacional, entre elas a execução integral, garantindo consistência e contemplando o controle de concorrência. O workflow é um conjunto de tarefas e interações organizadas de modo que forneça uma funcionalidade ao sistema, provendo a automatização de processos complexos, através da composição de serviços. Tal composição deve ser executada de forma transacional, processando as operações com consistência. A execução de workflows oriundos de domínios diferentes, faz com que os serviços que estão sendo utilizados, não possuam ciência do contexto da execução, podendo gerar atendimentos que não sejam justos, causando situações de deadlock e de starvation. Este trabalho apresenta estratégias para a execução de workflows em domínios distintos, que requisitam múltiplos serviços de um mesmo conjunto, sem a necessidade de um coordenador central, de forma transacional. O atendimento a requisição contempla uma política justa na utilização do recurso que impede a ocorrência de deadlock ou de starvation para os workflows em execução. Os experimentos realizados neste trabalho mostram que o sistema desenvolvido, aplicando as estratégias propostas, executa as composições de serviços de maneira transacional, atendendo as requisições com justiça, livre de deadlock e starvation, mantendo o sistema independente e autônomo. / Web Services are increasing software development possibilities, among then service composition. Service composition introduces new issues on computational environment, such as the whole service execution, ensuring consistency and concurrency control. Workflow is a set of organized tasks and interactions in order to provide functionality to the system, automating complex process through composition service. Such composition must be performed by transactional support, performing operations consistently. The workflow execution from different domain clients sharing the same composition make these clients ignore the execution context. It may cause inconsistencies, from unfair attendance to deadlock or starvation. This work depicts strategies for workflow execution from different domains, requesting multiple services from the same composition, without a centralized coordinator, in transactional way. The request attendance contains a fair policy for resource usage and consumption to avoid deadlock and starvation. Applying the proposed strategy on the experiments performed in this work, it confirms that the developed system executes service composition with transactional support, avoiding deadlock or starvation, keeping the whole system autonomous and independent.

Sistemas multi-agentes devem oferecer recursos suficientes para que seus agentes possam interagir de maneira satisfatória e atingir seus objetivos. Um exemplo de recurso é um conjunto de dados armazenados em algum tipo de mecanismo de persistência, como um sistema gerenciador de banco de dados. O acesso a dados deve ser possível mesmo que eles estejam distribuídos, fato inclusive que também caracteriza os sistemas multi-agentes. Assim, este trabalho apresenta um sistema chamado DASE cujo objetivo é prover a agentes o acesso a dados distribuídos de forma simples e transparente, ou seja, independentemente da complexidade que o ambiente dos agentes possui e das peculiaridades do Sistema de Banco de Dados Distribuído. O DASE suporta qualquer Sistema Gerenciador de Banco de Dados, seja ele centralizado ou distribuído, desde que o mesmo esteja em conformidade com o JDBC. Além disso, oferece recursos importantes como controle de concorrência, suporte a ambientes de dados simultâneos e uso de sentenças de acesso a dados pré-definidas e parametrizadas. Todos os aspectos mais importantes analisados durante o projeto deste sistema estão descritos neste trabalho, evidenciando e justificando o porquê de cada decisão que certamente refletiram no funcionamento e comportamento do DASE. O sistema foi implementado de acordo com o seu projeto, resultando em uma versão funcional e estável, o que foi comprovado através de seu uso em um projeto que envolvia sistemas multiagentes e controle de tráfego aéreo. Além disso, alguns testes de análise de desempenho considerando cenários variados foram realizados. / Multi-agent systems must offer the needed resources to allow their agents to interact and to reach their goals. An example of resource is a set of data stored in any kind of resource manager, such as a database management system. Data access must be possible even if the data is distributed, characteristic that is also present in multi-agent systems. Thus, this work describes a system whose objective is to provide to agents distributed data access in a simple and transparent way, in other words, hiding the agent environment and complexities related to distributed database systems. DASE supports any database management system, centralized or distributed, in compliance with JDBC (Java Database Connectivity). In addition it offers important features, such as concurrency control, simultaneous data environments and stored SQL sentences. All challenges and important aspects overcome in order to design and implement DASE are described, explaining and justifying every decision that in some way had a participation to form DASE set of functions and behavior. The system was implemented following its design, resulting in a functional and stable version, what could be verified through its adoption in a project based on multiagent systems and air traffic control systems. In addition, a plenty of performance tests were done regarding different scenarios.

Sistemas multi-agentes devem oferecer recursos suficientes para que seus agentes possam interagir de maneira satisfatória e atingir seus objetivos. Um exemplo de recurso é um conjunto de dados armazenados em algum tipo de mecanismo de persistência, como um sistema gerenciador de banco de dados. O acesso a dados deve ser possível mesmo que eles estejam distribuídos, fato inclusive que também caracteriza os sistemas multi-agentes. Assim, este trabalho apresenta um sistema chamado DASE cujo objetivo é prover a agentes o acesso a dados distribuídos de forma simples e transparente, ou seja, independentemente da complexidade que o ambiente dos agentes possui e das peculiaridades do Sistema de Banco de Dados Distribuído. O DASE suporta qualquer Sistema Gerenciador de Banco de Dados, seja ele centralizado ou distribuído, desde que o mesmo esteja em conformidade com o JDBC. Além disso, oferece recursos importantes como controle de concorrência, suporte a ambientes de dados simultâneos e uso de sentenças de acesso a dados pré-definidas e parametrizadas. Todos os aspectos mais importantes analisados durante o projeto deste sistema estão descritos neste trabalho, evidenciando e justificando o porquê de cada decisão que certamente refletiram no funcionamento e comportamento do DASE. O sistema foi implementado de acordo com o seu projeto, resultando em uma versão funcional e estável, o que foi comprovado através de seu uso em um projeto que envolvia sistemas multiagentes e controle de tráfego aéreo. Além disso, alguns testes de análise de desempenho considerando cenários variados foram realizados. / Multi-agent systems must offer the needed resources to allow their agents to interact and to reach their goals. An example of resource is a set of data stored in any kind of resource manager, such as a database management system. Data access must be possible even if the data is distributed, characteristic that is also present in multi-agent systems. Thus, this work describes a system whose objective is to provide to agents distributed data access in a simple and transparent way, in other words, hiding the agent environment and complexities related to distributed database systems. DASE supports any database management system, centralized or distributed, in compliance with JDBC (Java Database Connectivity). In addition it offers important features, such as concurrency control, simultaneous data environments and stored SQL sentences. All challenges and important aspects overcome in order to design and implement DASE are described, explaining and justifying every decision that in some way had a participation to form DASE set of functions and behavior. The system was implemented following its design, resulting in a functional and stable version, what could be verified through its adoption in a project based on multiagent systems and air traffic control systems. In addition, a plenty of performance tests were done regarding different scenarios.