How deeply does Latency cover quorum?

Defines the majority formula and latency consequence without detailing consensus protocol internals.

Quorum

As explained in Latency

A quorum is a majority subset of nodes whose agreement is sufficient for a distributed operation to complete.

A quorum is a majority subset of nodes whose agreement lets a distributed operation complete. For a cluster of N nodes, the quorum is (N/2) + 1. section 2.4

Quorums determine both agreement and response latency:

A three-node cluster requires two agreeing nodes; a five-node cluster requires three. section 2.4
Consensus algorithms such as Raft, Paxos, and Viewstamped Replication use majority agreement to replicate a state machine with strong consistency. section 2.4
Quorum compounding waits for a majority rather than every parallel component, but latency variability and tail latency still matter. section 2.4

Three-node cluster

When three nodes process an operation in parallel, completion requires responses from any two nodes. The slowest node does not determine completion unless it is needed to reach the majority. section 2.4

How Latency covers it

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Also explained in

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Kafka for ArchitectsA quorum architecture commits replicated state only after a majority of participating voters acknowledge the update.
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ScyllaDB in ActionThe QUORUM consistency level requires a majority of replicas for a key to acknowledge an operation.
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Elasticsearch in Action, Second EditionA quorum is the minimum number of eligible participants whose acknowledgments are required to authorize an operation in a distributed system.
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Think Distributed SystemsA quorum is a sufficient subset of distributed participants whose agreement or participation allows a decision to be made safely.

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Related concepts

consensusused by · Consensus is sufficient agreement among participants or processes on a shared decision, value, state, assessment, or outcome.
master-eligible nodehas part · A master-eligible node is an Elasticsearch node assigned the master role and therefore able to vote in master elections and become the elected master.
consistency levelkind of · A selectable database setting that determines how many replicas or nodes must participate in an operation and what consistency it provides.
data lossaddresses · Data loss is the destruction, corruption, deletion, or unavailability of information that is expected to be retained or remain usable.
leader electionused by · Leader election is a distributed coordination process that selects one eligible participant to act as leader or coordinator.

This explainer was generated by Manning's knowledge graph from the text of Latency. The section links point to the parts of the book it draws on.