Transaktionen in föderierten Datenbanksystemen unter eingeschränkten Isolation Levels

Atomarität und Isolation von Transaktionen sind Schlüsseleigenschaften fortgeschrittener Anwendungen in föderierten Systemen, die aus verteilten, heterogenen Komponenten bestehen. Während Atomarität von praktisch allen realen Systemen durch das Zweiphasen- Commitprotokoll gewährleistet wird, unterstützt kein System eine explizite föderierte Concurrency Control. In der Literatur wurden zwar zahlreiche Lösungsansätze vorgeschlagen, doch sie haben wenig Einfluss auf Produkte genommen, weil sie die weitverbreiteten Isolation Levels nicht berücksichtigen, die Applikationen Optimierungsmöglichkeiten auf Kosten einer eingeschränkten Kontrolle über die Konsistenz der Daten erlauben. Diese Arbeit vergleicht zunächst existierende Definitionen für Isolation Levels und entwickelt eine neuartige, formale Charakterisierung für Snapshot Isolation, dem Isolation Level des Marktführers Oracle. Anschließend werden Algorithmen zur föderierten Concurrency Control vorgestellt, die beweisbar auch unter lokaler Snapshot Isolation die korrekte Ausführung föderierter Transaktionen gewährleisten, und Isolation Levels für föderierte Transaktionen diskutiert. Die Algorithmen sind in ein prototypisches föderiertes System integriert. Performancemessungen an diesem Prototyp zeigen ihre praktische Einsetzbarkeit.Atomicity and isolation of transactions are key requirements of advanced applications in federated systems consisting of distributed and heterogeneous components. While all existing federated systems support atomicity using the two-phase commit protocol, they lack support for federated concurrency control. Many possible solutions have been proposed in the literature, but they failed to make impact on real systems because they completely ignored the widely used concept of isolation levels, which offer optimization options to applications at the cost of less rigorous control over data consistency. This thesis compares existing definitions for isolation levels and develops a new characterization for Snapshot Isolation, an isolation level provided by Oracle, the market leader in the database field. We present algorithms for federated concurrency control that provably guarantee the correct execution of federated transactions even under local Snapshot Isolation, and discuss isolation levels for federated transactions. The algorithms are integrated into a federated system prototype. Performance measurements with this prototype show the practical viability of the developed methods

Transaktionen in föderierten Datenbanksystemen unter eingeschränkten Isolation Levels

Atomarität und Isolation von Transaktionen sind Schlüsseleigenschaften fortgeschrittener Anwendungen in föderierten Systemen, die aus verteilten, heterogenen Komponenten bestehen. Während Atomarität von praktisch allen realen Systemen durch das Zweiphasen- Commitprotokoll gewährleistet wird, unterstützt kein System eine explizite föderierte Concurrency Control. In der Literatur wurden zwar zahlreiche Lösungsansätze vorgeschlagen, doch sie haben wenig Einfluss auf Produkte genommen, weil sie die weitverbreiteten Isolation Levels nicht berücksichtigen, die Applikationen Optimierungsmöglichkeiten auf Kosten einer eingeschränkten Kontrolle über die Konsistenz der Daten erlauben. Diese Arbeit vergleicht zunächst existierende Definitionen für Isolation Levels und entwickelt eine neuartige, formale Charakterisierung für Snapshot Isolation, dem Isolation Level des Marktführers Oracle. Anschließend werden Algorithmen zur föderierten Concurrency Control vorgestellt, die beweisbar auch unter lokaler Snapshot Isolation die korrekte Ausführung föderierter Transaktionen gewährleisten, und Isolation Levels für föderierte Transaktionen diskutiert. Die Algorithmen sind in ein prototypisches föderiertes System integriert. Performancemessungen an diesem Prototyp zeigen ihre praktische Einsetzbarkeit.Atomicity and isolation of transactions are key requirements of advanced applications in federated systems consisting of distributed and heterogeneous components. While all existing federated systems support atomicity using the two-phase commit protocol, they lack support for federated concurrency control. Many possible solutions have been proposed in the literature, but they failed to make impact on real systems because they completely ignored the widely used concept of isolation levels, which offer optimization options to applications at the cost of less rigorous control over data consistency. This thesis compares existing definitions for isolation levels and develops a new characterization for Snapshot Isolation, an isolation level provided by Oracle, the market leader in the database field. We present algorithms for federated concurrency control that provably guarantee the correct execution of federated transactions even under local Snapshot Isolation, and discuss isolation levels for federated transactions. The algorithms are integrated into a federated system prototype. Performance measurements with this prototype show the practical viability of the developed methods

Aviation System Analysis Capability Executive Assistant Design

In this technical document, we describe the design developed for the Aviation System Analysis Capability (ASAC) Executive Assistant (EA) Proof of Concept (POC). We describe the genesis and role of the ASAC system, discuss the objectives of the ASAC system and provide an overview of components and models within the ASAC system, and describe the design process and the results of the ASAC EA POC system design. We also describe the evaluation process and results for applicable COTS software. The document has six chapters, a bibliography, three appendices and one attachment

The CORBA object group service:a service approach to object groups in CORBA

Distributed computing is one of the major trends in the computer industry. As systems become more distributed, they also become more complex and have to deal with new kinds of problems, such as partial crashes and link failures. To answer the growing demand in distributed technologies, several middleware environments have emerged during the last few years. These environments however lack support for "one-to-many" communication primitives; such primitives greatly simplify the development of several types of applications that have requirements for high availability, fault tolerance, parallel processing, or collaborative work. One-to-many interactions can be provided by group communication. It manages groups of objects and provides primitives for sending messages to all members of a group, with various reliability and ordering guarantees. A group constitutes a logical addressing facility: messages can be issued to a group without having to know the number, identity, or location of individual members. The notion of group has proven to be very useful for providing high availability through replication: a set of replicas constitutes a group, but are viewed by clients as a single entity in the system. This thesis aims at studying and proposing solutions to the problem of object group support in object-based middleware environments. It surveys and evaluates different approaches to this problem. Based on this evaluation, we propose a system model and an open architecture to add support for object groups to the CORBA middle- ware environment. In doing so, we provide the application developer with powerful group primitives in the context of a standard object-based environment. This thesis contributes to ongoing standardization efforts that aim to support fault tolerance in CORBA, using entity redundancy. The group architecture proposed in this thesis — the Object Group Service (OGS) — is based on the concept of component integration. It consists of several distinct components that provide various facilities for reliable distributed computing and that are reusable in isolation. Group support is ultimately provided by combining these components. OGS defines an object-oriented framework of CORBA components for reliable distributed systems. The OGS components include a group membership service, which keeps track of the composition of object groups, a group multicast service, which provides delivery of messages to all group members, a consensus service, which allows several CORBA objects to resolve distributed agreement problems, and a monitoring service, which provides distributed failure detection mechanisms. OGS includes support for dynamic group membership and for group multicast with various reliability and ordering guarantees. It defines interfaces for active and primary-backup replication. In addition, OGS proposes several execution styles and various levels of transparency. A prototype implementation of OGS has been realized in the context of this thesis. This implementation is available for two commercial ORBs (Orbix and VisiBroker). It relies solely on the CORBA specification, and is thus portable to any compliant ORB. Although the main theme of this thesis deals with system architecture, we have developed some original algorithms to implement group support in OGS. We analyze these algorithms and implementation choices in this dissertation, and we evaluate them in terms of efficiency. We also illustrate the use of OGS through example applications

Group communications and database replication:techniques, issues and performance

Databases are an important part of today's IT infrastructure: both companies and state institutions rely on database systems to store most of their important data. As we are more and more dependent on database systems, securing this key facility is now a priority. Because of this, research on fault-tolerant database systems is of increasing importance. One way to ensure the fault-tolerance of a system is by replicating it. Replication is a natural way to deal with failures: if one copy is not available, we use another one. However implementing consistent replication is not easy. Database replication is hardly a new area of research: the first papers on the subject are more than twenty years old. Yet how to build an efficient, consistent replicated database is still an open research question. Recently, a new approach to solve this problem has been proposed. The idea is to rely on some communication infrastructure called group communications. This infrastructure offers some high-level primitives that can help in the design and the implementation of a replicated database. While promising, this approach to database replication is still in its infancy. This thesis focuses on group communication-based database replication and strives to give an overall understanding of this topic. This thesis has three major contributions. In the structural domain, it introduces a classification of replication techniques. In the qualitative domain, an analysis of fault-tolerance semantics is proposed. Finally, in the quantitative domain, a performance evaluation of group communication-based database replication is presented. The classification gives an overview of the different means to implement database replication. Techniques described in the literature are sorted using this classification. The classification highlights structural similarities of techniques originating from different communities (database community and distributed system community). For each category of the classification, we also analyse the requirements imposed on the database component and group communication primitives that are needed to enforce consistency. Group communication-based database replication implies building a system from two different components: a database system and a group communication system. Fault-tolerance is an end-to-end property: a system built from two components tends to be as fault-tolerant as the weakest component. The analysis of fault-tolerance semantics show what fault-tolerance guarantee is ensured by group communication based replication techniques. Additionally a new faulttolerance guarantee, group-safety, is proposed. Group-safety is better suited to group communication-based database replication. We also show that group-safe replication techniques can offer improved performance. Finally, the performance evaluation offers a quantitative view of group communication based replication techniques. The performance of group communication techniques and classical database replication techniques is compared. The way those different techniques react to different loads is explored. Some optimisation of group communication techniques are also described and their performance benefits evaluated

Architecting integrated internet of things systems

IoT (Internet of Things) enables anytime and anyplace connectivity for anything by linking the objects of the real world with the virtual world. In the near future, it is predicted that more than 50 billion of things will be connected to the internet. This will lead to many different IoT- based systems that will have a huge impact on the society. Often, these IoT systems will not be standalone but will be composed with other different systems to create additional value. Hence, with the heterogeneity and the integration of IoT-based systems with other IoT-based or non-IoT-based systems has become an important challenge. In this thesis, the main objective is to analyze, design and integrate IoT-based systems and to answer the following research questions: RQ1. What are the characteristic features of IoT systems? RQ2. How to design the architecture for an IoT-based system? RQ3. What are the identified obstacles of the data distribution (DDS) middleware? RQ4. What are the solution directions for the identified obstacles of DDS? RQ5. What are the approaches for integrating multiple IoT-based systems? RQ6. How to design a DDS-based IoT system? RQ7. How to derive feasible deployment alternatives for DDS-based systems? In order to answer these research questions, three different research methodologies were used: Systematic Literature Review, Design Science Research, and Case Study Research. In chapter 2, we have applied a feature driven domain analysis of IoT systems. We have presented the reference architecture for IoT and discussed the corresponding layers. Among these layers, we have focused on the session layer of the IoT. The protocols in this layer are related with the communication sessions of the IoT systems and hence determine the communication characteristics of the IoT systems. We have presented the common and variant features of the most commonly used session layer protocols, namely AMQP, CoAP, DDS, MQTT, and XMPP which are used for communication between M2M (machine-to- machine), M2S (machine-to-server), and S2S (server-to-server). Further, we have provided an evaluation framework to compare session layer communication protocols. Among these protocols, we focused on the DDS that is mainly used for M2M communication in Industrial Internet of Things (IIoT). In chapter 3, we have described an architecture design method for architecting IoT systems for the Farm Management Information Systems (FMIS) domain. Hereby, we have also developed a family feature diagram to represent the common and variant features of IoT- based FMIS. In order to illustrate our approach, we have performed a systematic case study approach including the IoT-based wheat and tomato production with IoT-based FMIS. The case study research showed that the approach was both effective and practical. In chapter 4, we have presented the method for designing integrated IoT systems. We showed that integration of IoT-based systems can be at different layers including session layer, cloud layer and application layer. Further we have shown that the integration is typically carried out based on well-defined patterns, that is, generic solutions structures for recurring problems. We have systematically compiled and structured the 15 different integration patterns which can be used in different combinations and likewise supporting the composition of different IoT systems. We have illustrated the use of example patterns in a smart city case study and have shown that the systematic structuring of the integration patterns is useful for integrating IoT systems. A systematic research methodology has been applied in chapter 5 to identify the current obstacles to adopt DDS and their solution directions. We have selected 34 primary studies among the 468 identified papers since the introduction of DDS in 2003. We identified 11 basic categories of problems including complexity of DDS configuration, performance prediction, measurement and optimization, implementing DDS, DDS integration over WAN, DDS using wireless networks and mobile computing, interoperability among DDS vendor implementations, data consistency in DDS, reliability in DDS, scalability in DDS, security, and integration with event-based systems. We have adopted feature diagrams to summarize and provide an overview of the identified problem and their solutions defined in the primary studies. DDS based architecture design for IoT systems is presented in chapter 6. DDS is considered to be a potential middleware for IoT because of its focus on event-driven communication in which quality of service is also explicitly defined. We provide a systematic approach to model the architecture for DDS-based IoT in which we adopted architecture viewpoints for modeling DDS, IoT and DDS-based IoT systems. We have integrated and represented the architecture models that can be used to model DDS-based IoT systems for various application domains. When designing DDS-based systems typically multiple different alternatives can be derived. Chapter 7 presents an approach for deriving feasible DDS configuration alternatives. For this we have provided a systematic approach for extending the DDS UML profile and developed an extensible tool framework Deploy-DDS to derive feasible deployment alternatives given the application model, the physical resources, and the execution configurations. The tool framework Deploy-DDS implements a set of predefined algorithms and can be easily extended with new algorithms to support the system architect. We have evaluated the approach and the tool framework for a relevant IoT case study on smart city engineering. Chapter 8 concludes the thesis by summarizing the contributions.</p

Local Coordination for Interpersonal Communication Systems

The decomposition of complex applications into modular units is anacknowledged design principle for creating robust systems and forenabling the flexible re-use of modules in new applicationcontexts. Typically, component frameworks provide mechanisms and rulesfor developing software modules in the scope of a certain programmingparadigm or programming language and a certain computing platform. Forexample, the JavaBeans framework is a component framework for thedevelopment of component-based systems -- in the Java environment.In this thesis, we present a light-weight, platform-independentapproach that views a component-based application as a set of ratherloosely coupled parallel processes that can be distributed on multiplehosts and are coordinated through a protocol. The core of ourframework is the Message Bus (Mbus): an asynchronous, message-orientedcoordination protocol that is based on Internet technologies andprovides group communication between application components.Based on this framework, we have developed a local coordinationarchitecture for decomposed multimedia conferencing applications thatis designed for endpoint and gateway applications. One element of thisarchitecture is an Mbus-based protocol for the coordination of callcontrol components in conferencing applications

From Resilience-Building to Resilience-Scaling Technologies: Directions -- ReSIST NoE Deliverable D13

This document is the second product of workpackage WP2, "Resilience-building and -scaling technologies", in the programme of jointly executed research (JER) of the ReSIST Network of Excellence. The problem that ReSIST addresses is achieving sufficient resilience in the immense systems of ever evolving networks of computers and mobile devices, tightly integrated with human organisations and other technology, that are increasingly becoming a critical part of the information infrastructure of our society. This second deliverable D13 provides a detailed list of research gaps identified by experts from the four working groups related to assessability, evolvability, usability and diversit

Experiences with Building a Federated Transaction Manager based on CORBA OTS

. Federated transaction management is needed to ensure the consistency of data that is distributed across multiple, largely autonomous, and possibly heterogeneous component databases and accessed by both global and local transactions. The problem of how to achieve global serializability has been intensively studied in the literature, but none of the proposed approaches can be considered as a universally &apos;best&apos; strategy. Rather a federated transaction manager should support a suite of strategies and allow selecting the most suitable protocol for each application. Furthermore, it should not only concentrate on the idealized correctness criterion of serializability, but also oer support for dierent isolation levels, which are widely used in existing database systems. This paper presents the design and implementation of a CORBA-based customizable transaction manager for a federate database system. It gives a discussion of how OTS, the CORBA approach to distributed transactions, can be us..