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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Snapple : A distributed, fault-tolerant, in-memory key-value store using Conflict-Free Replicated Data Types / Snapple : En distribuerad feltolerant nyckelvärdesdatabas i RAM-minnet baserad på konfliktfria replikerade datatyper

Stenberg, Johan January 2016 (has links)
As services grow and receive more traffic, data resilience through replication becomes increasingly important. Modern large-scale Internet services such as Facebook, Google and Twitter serve millions of users concurrently. Replication is a vital component of distributed systems. Eventual consistency and Conflict-Free Replicated Data Types (CRDTs) are suggested as an alternative to strong consistency systems. This thesis implements and evaluates Snapple, a distributed, fault-tolerant, in-memory key-value database based on CRDTs running on the Java Virtual Machine. Snapple supports two kinds of CRDTs, an optimized implementation of the OR-Set and version vectors. Performance measurements show that the Snapple system is significantly faster than Riak, a persistent database based on CRDTs, but has a factor 5x - 2.5x lower throughput than Redis, a popular in-memory key-value database written in C. Snapple is a prototype-implementation but might be a viable alternative to Redis if the user wants the consistency guarantees CRDTs provide. / När internet-baserade tjänster växer och får mer trafik blir data replikering allt viktigare. Moderna storskaliga internet-baserade tjänster såsom Facebook, Google och Twitter hanterar miljoner av förfrågningar från användare samtidigt. Datareplikering är en vital komponent av distribuerade system. Eventuell synkronisering och Konfliktfria Replikerade Datatyper (CRDTs) är föreslagna som alternativ till direkt synkronisering. Denna uppsats implementerar och evaluerar Snapple, en distribuerad feltolerant nyckelvärdesdatabas i RAM-minnet baserad på CRDTs och som exekverar på Javas virtuella maskin. Snapple stödjer två sorters CRDTs, den optimerade implementationen av observera-ta-bort setet och versionsvektorer. Prestanda-mätningar visar att Snapple-systemet är mycket snabbare än Riak, en persistent databas baserad på CRDTs. Snapple visar sig ha 5x - 2.5x lägre genomströmning än Redis, en popular i-minnet nyckel-värdes databas skriven i C. Snapple är en prototyp men CRDT-stödda system kan vara ett värdigt alternativ till Redis om användaren vill ta del av synkroniseringsgarantierna som CRDTs tillhandahåller.
2

Mobile Modeling with Real-Time Collaboration Support

Härtwig, Max 02 March 2022 (has links)
Modeling is an essential discipline that is especially important in the field of software engineering. Students and developers alike employ models to describe systems on an abstract level, capture requirements, and communicate with other teams. For that purpose, UML diagrams are usually the instrument of choice. Over the course of the last decade, mobile devices increased in prevalence and popularity and flexible work arrangements were introduced in a larger number of workplaces. Effective collaboration is more important than ever. However, the tools have not kept up with these developments. There exists no semantics-aware mobile modeling application that supports collaboration in real time, a gap in the market. This thesis investigates existing applications in the mobile modeling space and their shortcomings, technologies for developing cross-platform apps, and methodologies for facilitating conflict-free collaboration. Based on the findings, it conceptualizes and implements CoMod, a proof of concept allowing users to collaboratively edit UML class diagrams in real time. The system consists of a Flutter-based client application for Android and iOS and a Node.js-based server executable. These components utilize conflict-free replicated data types (CRDTs) to merge participants' changes and communicate via WebSocket connections. Moreover, CoMod's feasibility is evaluated by means of a case study investigating the system's scalability and performance characteristics. It has been shown that CoMod is able to handle common use cases arising in software engineering teams or group projects at university. It is further kept sufficiently general to allow other types of models to be supported without having to alter the entire system.:1 Introduction 1.1 Requirements 1.2 Problem Description 1.3 Objectives 1.4 Structure 2 Background 2.1 Software Modeling 2.1.1 Unified Modeling Language 2.2 Cross-Platform Application Development 2.2.1 Web Apps 2.2.2 Hybrid Apps 2.2.3 Native cross-platform apps 2.2.4 Summary 2.3 Real-Time Collaboration 2.3.1 Conflict-Free Replicated Data Types (CRDTs) 2.3.2 Operational Transformation 3 Related Work 3.1 Astah UML 3.2 Lucidchart 3.3 System Designer 3.4 Summary 4 Concept 4.1 Objectives 4.2 User Interface 4.3 Data Model 4.4 Collaboration 4.4.1 Conflict handling 4.4.2 System architecture 4.4.3 Client-server communication 4.5 Summary 5 Solution 5.1 Client 5.1.1 Walkthrough 5.1.2 Data model 5.1.3 JavaScript subsystem 5.1.4 Dependencies 5.2 Server 5.2.1 Dependencies 5.3 Collaboration 5.3.1 Client-server communication 5.3.2 Client data flow 5.4 Testing 5.4.1 Unit tests 5.4.2 Integration tests 5.4.3 End-to-end tests 5.5 Extensibility 6 Evaluation 6.1 Case Study 6.2 Technical Analysis 6.2.1 Test data generator 6.2.2 Client analysis 6.2.3 Server analysis 6.3 Threats to Validity 7 Conclusion 7.1 Fulfillment of Objectives 7.2 Future Work Acronyms Bibliography
3

Garbage Collected CRDTs on the Web : Studying the Memory Efficiency of CRDTs in a Web Context

Rehn, Michael January 2020 (has links)
In today's connected society, where it is common to have several connected devices per capita, it is more important than ever that the data you need is omnipresent, i.e. its available when you need it, no matter where you are. We identify one key technology and platform that could be the future—peer-to-peer communication and the Web. Unfortunately, guaranteeing consistency and availability between users in a peer-to-peer network, where network partitions are bound to happen, can be a challenging problem to solve. To solve these problems, we turned to a promising category of data types called CRDTs—Conflict Free Replicated Data Types. By following the scientific tradition of reproduction, we build upon previous research of a CRDT framework, and adjust it work in a peer-to-peer Web environment, i.e. it runs on a Web browser. CRDTs makes use of meta-data to ensure consistency, and it is imperative to remove this meta-data once it no longer has any use—if not, memory usage grows unboundedly making the CRDT impractical for real-world use. There are different garbage collection techniques that can be applied to remove this meta-data. To investigate whether the CRDT framework and the different garbage collection techniques are suitable for the Web, we try to reproduce previous findings by running our implementation through a series of benchmarks. We test whether our implementation works correctly on the Web, as well as comparing the memory efficiency between different garbage collection techniques. In doing this, we also proved the correctness of one of these techniques. The results from our experiments showed that the CRDT framework was well-adjusted to the Web environment and worked correctly. However, while we could observe similar behaviour between different garbage collection techniques as previous research, we achieved lower relative memory savings than expected. An additional insight was that for long-running systems that often reset its shared state, it might be more efficient to not apply any garbage collection technique at all. There is still much work to be done to allow for omnipresent data on the Web, but we believe that this research contains two main takeaways. The first is that the general CRDT framework is well-suited for the Web and that it in practice might be more efficient to choose different garbage collection techniques, depending on your use-case. The second take-away is that by reproducing previous research, we can still advance the current state of the field and generate novel knowledge—indeed, by combining previous ideas in a novel environment, we are now one step closer to a future with omnipresent data. / I dagens samhälle är vi mer uppkopplade än någonsin. Tack vare det faktum att vi nu ofta har fler än en uppkopplad enhet per person, så är det viktigare än någonsin att ens data är tillgänglig på alla ens enheter–oavsett vart en befinner sig. Två tekniker som kan möjliggöra denna ``allnärvaro'' av data är Webben, alltså kod som körs på en Webbläsare, tillsammans med peer-to-peer-kommunikation; men att säkerställa att distribuerad data både är tillgänglig och likadan för alla enheter är svårt, speciellt när enhetens internetanslutning kan brytas när som helst. Conflict-free replicated data-types (CRDT:er) är en lovande klass av datatyper som löser just dessa typer av problem i distribuerade system; genom att använda sig av meta-data, så kan CRDT:er fortsätta fungera trots att internetanslutningen brutits. Dessutom är de garanterade att konvergera till samma sluttillstånd när anslutningen upprättas igen. Däremot lider CRDT:er av ett speciellt problem–denna meta-data tar upp mycket minne trots att den inte har någon användning efter en stund. För att göra datatypen mer minneseffektiv så kan meta-datan rensas bort i en process som kallas för skräpsamling. Vår idé var därför att reproducera tidigare forskning om ett ramverk för CRDT:er och försöka anpassa denna till att fungera på Webben. Vi reproducerar dessutom olika metoder för skräpsamling för att undersöka om de, för det första fungerar på Webben, och för det andra är lika effektiv i denna nya miljö som den tidigare forskningen pekar på. Resultaten från våra experiment visade att CRDT-ramverket och dess olika skräpsamlingsmetoder kunde anpassas till att fungera på Webben. Däremot så noterade vi något högre relativ minnesanvändning än vad vi har förväntat oss, trots att beteendet i stort var detsamma som den tidigare forskningen. En ytterligare upptäckt vad att i vissa specifika fall så kan det vara mer effektivt att inte applicera någon skräpsamling alls. Trots att det är mycket arbete kvar för att använder CRDT:er peer-to-peer på Webben för att möjliggöra ``allnärvarande'' data, så innehåller denna uppsats två huvudsakliga punkter. För det första så fungerar det att anpassa CRDT-ramverket och dess olika skräpsamlingsmetoder till Webben, men ibland är det faktiskt bättre att inte applicera någon skräpsamling alls. För det andra så visas vikten av att reproducera tidigare forskning–inte bara visar uppsatsen att tidigare CRDT-forskning kan appliceras i andra miljöer, dessutom kan ny kunskap hämtas ur en sådan reproducering.

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