合意形成アルゴリズム（コンセンサス・アルゴリズム）
ネットワーク全体で同意を得るためのルール。
Causes: 1. Network [latency](/ja/terms/network-latency) (Natural forks). 2. 51% Attacks (Malicious reorgs). 3. Buggy clients. Effects: Transaction reversals, increased confirmation times, potential for double-spending. Key metrics: Reorg depth, Orphan block rate.
graph LR
Center["合意形成アルゴリズム（コンセンサス・アルゴリズム）"]:::main
Rel_distributed_computing["distributed-computing"]:::related -.-> Center
click Rel_distributed_computing "/terms/distributed-computing"
Rel_double_spending["double-spending"]:::related -.-> Center
click Rel_double_spending "/terms/double-spending"
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classDef pre fill:#0f172a,stroke:#3b82f6,color:#94a3b8,rx:5,ry:5;
classDef child fill:#0f172a,stroke:#10b981,color:#94a3b8,rx:5,ry:5;
classDef related fill:#0f172a,stroke:#8b5cf6,stroke-dasharray: 5 5,color:#94a3b8,rx:5,ry:5;
linkStyle default stroke:#4b5563,stroke-width:2px;
🧒 5歳でもわかるように説明
バラバラな場所にいるたくさんの人たちが、嘘つきに騙されずに「今の正しい記録はこれだ！」とみんなで決めるためのルールのことです。
🤓 Expert Deep Dive
The probability of a reorg decreases exponentially with block depth. In Bitcoin, 6 confirmations (~1 hour) is considered statistically safe against deep reorgs. Technically, when a reorg occurs, the node identifies the 'Common Ancestor' of the two branches, rolls back the state to that point, and then reapplies the transactions from the new winning branch. Transactions from the discarded blocks are returned to the 'Mempool' and usually included in subsequent blocks. Modern Proof-of-Stake (PoS) systems like Ethereum 2.0 introduce 'Finality' (Casper FFG), where after a certain point (~12.8 minutes), a reorg becomes mathematically impossible without destroying a significant portion of the total staked capital (Slashing).