A categorization scheme for concurrency control protocols in distributed databases

The problem of concurrency control in distributed databases is very complex. As a result, a great number of control algorithms have been proposed in recent years. This research is aimed at the development of a viable categorization scheme for these various algorithms. The scheme is based on the theoretical concept of serializability, but is qualitative in nature. An important class of serializable execution sequences, conflict-preserving-serializable, leads to the identification of fundamental attributes common to all algorithms included in this study. These attributes serve as the underlying philosophy for the categorization scheme. Combined with the two logical approaches of prevention and correction of nonserializability, the result is a flexible and extensive categorization scheme which accounts for all algorithms studied and suggests the possibility of new algorithms

Optimistic replication

Data replication is a key technology in distributed data sharing systems, enabling higher availability and performance. This paper surveys optimistic replication algorithms that allow replica contents to diverge in the short term, in order to support concurrent work practices and to tolerate failures in low-quality communication links. The importance of such techniques is increasing as collaboration through wide-area and mobile networks becomes popular. Optimistic replication techniques are different from traditional “pessimistic ” ones. Instead of synchronous replica coordination, an optimistic algorithm propagates changes in the background, discovers conflicts after they happen and reaches agreement on the final contents incrementally. We explore the solution space for optimistic replication algorithms. This paper identifies key challenges facing optimistic replication systems — ordering operations, detecting and resolving conflicts, propagating changes efficiently, and bounding replica divergence — and provides a comprehensive survey of techniques developed for addressing these challenges

Shelfaware: Accelerating Collaborative Awareness with Shelf CRDT

Collaboration has become a key feature of modern software, allowing teams to work together effectively in real-time while in different locations. In order for a user to communicate their intention to several distributed peers, computing devices must exchange high-frequency updates with transient metadata like mouse position, text range highlights, and temporary comments. Current peer-to-peer awareness solutions have high time and space complexity due to the ever-expanding logs that each client must maintain in order to ensure robust collaboration in eventually consistent environments. This paper proposes an awareness Conflict-Free Replicated Data Type (CRDT) library that provides the tooling to support an eventually consistent, decentralized, and robust multi-user collaborative environment. Our library is tuned for rapid iterative updates that communicate fine-grained user actions across a network of collaborators. Our approach holds memory constant for subsequent writes to an existing key on a shared resource and completely prunes stale data from shared documents. These features allow us to keep the CRDT\u27s memory footprint small, making it a feasible solution for memory constrained applications. Results show that our CRDT implementation is comparable to or exceeds the performance of similar data structures in high-frequency read/write scenarios

Blockchain Application - Case Study on Hyperledger Fabric

Usalduse keskkonna saamiseks kasutatakse kolmandaid osapooli ja nende tarkvara platvorme. Plokiahela tehnoloogia ja nutikaid lepingud on üks võimalus, kuidas välistada kolmas osapool. Üks viimased turule tulnud vabatarkvara platvorme on Hyperledger Fabric - modulaarne süsteem, mis kasutab üldkasutavaid programmeerimskeeli nutikate lepingute keelena. See avardab platvormi kasutamist ettevõtte tarkvara loomisel. Võrdleme platvormi tavapäraste lahendustega ning uurime väljakutseid, mida pakub uus plokiahela põhine süsteem ja selle jaoks loodud nutika leping nimega chaincode. Selle töö käigus realiseeriti parkimiseks mõeldud rakendus, mille nutikas leping on kirjutatud Go programmeerimiskeeles.Töö käigus realiseerisime prototüübi, leidsime lahendused tehnilistele probleemidele, realiseerisime kasutusjuhud.To enable software platform to be used without a third trusted party, one of the possibilities is to use blockchain and smart contracts. One of the latest platform is open-source Hyperledger Fabric, a modular system that uses conventional programming languages for smart contracts. This opens up vast possibilities for using it product centric enterprise systems. In this paper we compare the platform to a conventional solution and study the challenges provided by the smart contract called chaincode. We implement a parking spot application for multisided market using smart contract and Go programming language. In the end we have a working prototype with solutions to technical problems, covering predetermined use cases