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Decentralized consensus protocols

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Abstract

The goal of decentralized consensus protocols is to exchange information among computers so that each computer acquires information held by every other computer in the system. The authors introduce a unifying framework which generalizes these decentralized consensus protocols. A necessary and sufficient property for consensus protocols, which uses k round of message exchange, is presented. S. Yuan and A.K. Agrawala's (1988) k -dimensional array based protocol can be viewed in this unifying framework. The authors introduce a novel class of protocols within the unifying framework, called quorum-based protocols. Quorum-based protocols are obtained by observing only the necessary properties which must be maintained. They use two rounds of message exchange (i.e. k =2) and have the property that the first and second rounds of message exchange use the same connection. This property may be exploited if the underlying network provides connection-oriented service. Quorum-based protocols include the centralized protocol and T.V. Lakshman and A.K. Agrawala's (1986) protocol. By applying finite projective planes directly, the authors obtain a protocol which reduces the number of required messages to half the number required in Lakshman and Agrawala's protocol
... Then, a read operation can always identify the most recent version of the data, and write conicts are also prevented. Quorums are also used in distributed systems for many other purposes such as mutual exclusion ( [1,11]), commit protocols ( [13]) and distributed consensus [9]. ...
Article
Recently there has been considerable interest in the study of replica-control protocols which are based on organizing several copies of an object into logical structures, such as rectangular grids. In addition to high availability, another objective in exploiting such structures is to improve the degree of load sharing in a system. In this paper, we extend the scope of grid structures to general grids, which allow holes in various positions of a rectangular structure and are useful to consider because they often produce availabilities that are higher than solid grids, where every position must be occupied by a node. We propose an improvement to the existing grid protocol, prove its optimality, and also compare its performance with the existing protocol in terms of availability. In addition, we also offer new insights into the performance of the grids, from both availability and load sharing points of view. Noting that the write availability of square grids tends to 0 for a large number...
... Then, a read operation can always identify the most recent version of the data, and write con icts are also prevented. Quorums are also used in distributed systems for many other purposes such as mutual exclusion ([1, 11]), commit protocols ([13]) and distributed consensus [9]. In addition to higher availability, a second advantage of replication is greater load sharing. ...
Conference Paper
Recently, there has been considerable interest in the study of replica-control protocols which are based on organizing several copies of an object into logical structures, such as rectangular grids. In addition to high availability, another objective in exploiting such structures is to improve the degree of load sharing in a system. The authors extend the scope of grid structures to general grids, which allow holes in various positions of a rectangular structure and are useful to consider because they often produce availabilities that are higher than solid grids, where every position must be occupied by a node. In addition to proposing an improvement to the existing grid protocol, new insights are offered into the performance of the grids, from both availability and load sharing points of view. Algorithms for designing grids to maximize availability independently and also in conjunction with a load sharing constraint are given
... Yuan and Agrawala's kdimensional array based protocol can be viewed in this unifying framework. We introduce a new class of protocols within the unifying framework, called quorumbased protocols 48]. ...
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m come true. ii Contents 1 Introduction 1 1.1 Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Definitions and Properties 7 2.1 Quorum Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.1 Quorum sets and coteries . . . . . . . . . . . . . . . . . . . 9 2.2.2 Bicoteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3 Applications 15 3.1 Decentralized Consensus Protocols . . . . . . . . . . . . . . . . . 15 3.1.1 Generalized consensus protocols . . . . . . . . . . . . . . . 16 3.1.2 Quorum-based consensus protocols . . . . . . . . . . . . . 19 3.2 Distributed Mutual Exclusion Algorithms . . . . . . . . . . . . . . 24 3.3 Replica Control Protocols . . . . . . . . . . . . . . . . . . . . . . 26 4 Related Research 30<F14.4
Chapter
Quorum systems are used to implement many coordination problems in distributed systems such as mutual exclusion, data replication, distributed consensus, and commit protocols. This paper presents a new class of quorum systems based on connected regions in planar graphs. This class has an intuitive geometric nature and is easy to visualize and map to the system topology. We show that for triangulated graphs, the resulting quorum systems are non-dominated, which is a desirable property. We study the performance of these systems in terms of their availability, load, and cost of failures. We formally introduce the concept of cost of failures and argue that it is needed to analyze the message complexity of quorum-based protocols. We show that quorums of triangulated graphs with bounded degree have optimal cost of failure. We study a particular member of this class, the triangle lattice. The triangle lattice has small quorum size, optimal load for its size, high availability, and optimal cost of failures. Its parameters are not matched by any other proposed system in the literature. We use percolation theory to study the availability of this system.
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