Computer Science

Consensus, explained

Consensus is the process by which distributed nodes agree on a value or sequence of decisions despite failures.
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Part of the Semantic Notion technical glossary.

Short Definition

Consensus is the process by which distributed nodes agree on a value or sequence of decisions despite failures.

Intuition

Consensus gives a cluster a shared answer even when machines crash or messages are delayed.

Technical Definition

Consensus protocols ensure agreement, validity, and termination properties under a defined failure model.

Example

A replicated log uses consensus so all nodes apply database writes in the same order.

Common Misunderstandings

Consensus is expensive compared with local decisions.
The guarantees depend on the failure model.

Same Category

More from Computer Science

AlgorithmAn algorithm is a precise procedure for solving a problem or computing a result.Byzantine Fault ToleranceByzantine fault tolerance is the ability of a distributed system to keep working even when some nodes behave arbitrarily or maliciously.CacheA cache stores recently or frequently used data in a faster location so future access is quicker.Cache CoherenceCache coherence is the property that multiple caches maintain a consistent view of shared data.CAP TheoremCAP theorem says a distributed data system cannot simultaneously guarantee consistency, availability, and partition tolerance during a network partition.ConcurrencyConcurrency is the ability of a system to make progress on multiple tasks during overlapping time periods.

Related Reading

Essays that use this concept

Computer ScienceThe Byzantine Generals Problem

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