A quorum system is a collection of subsets of nodes, called quorums, with the property that each pair of quorums have a non-empty intersection. Quorum systems are the key mathematical abstraction for ensuring consistency in fault-tolerant and highly available distributed computing. Critical for many applications since the early days of distributed computing, quorum systems have evolved from simple majorities of a set of processes to complex hierarchical collections of sets, tailored for general adversarial structures. The initial non-empty intersection property has been refined many times to account for, e.g., stronger (Byzantine) adversarial model, latency considerations or better availability. This monograph is an overview of the evolution and refinement of quorum systems, with emphasis on their role in two fundamental applications: distributed read/write storage and consensus. Table of Contents: Introduction / Preliminaries / Classical Quorum Systems / Classical Quorum-Based Emulations / Byzantine Quorum Systems / Latency-efficient Quorum Systems / Probabilistic Quorum Systems

マルコ・ヴコリッチが描くのは、デジタル社会を支える「合意」の数学的美学です。本作の真髄は、不確実な世界でいかに単一の真実を守り抜くかという、分散システムの「正義」を定義した点にあります。単純な過半数から悪意ある裏切りをも克服する構造へ至る変遷は、さながら論理学による壮大な叙事詩のような知的高揚感を与えてくれます。 著者は、可用性と効率の狭間で磨かれた「交差の美学」を鮮やかに解明します。分散型ストレージという現代の基盤を追うことは、混沌の中に秩序を見出す知性の軌跡を辿ることに他なりません。技術書の枠を超え、究極の信頼を追求する情熱が、行間から熱く伝わってくる一冊です。