{
  "slug": "quorum-intersection",
  "term": "Quorum intersection",
  "aliases": [
    "Read-write quorum overlap"
  ],
  "definition": "Quorum intersection is the property that every relevant pair of allowed quorums shares at least one replica.",
  "note": "For arbitrary R-member read sets and W-member write sets drawn from the same fixed N replicas, R + W > N guarantees overlap; this is the equal-vote case of quorum voting. [gifford] Two W-member write sets must overlap when 2W > N. These are set properties, not standalone consistency protocols.",
  "limitations": [
    {
      "text": "Intersection alone does not establish linearizability, repair coverage or persistent storage of acknowledged data.",
      "citationIds": [
        "guarantees",
        "gifford"
      ]
    }
  ],
  "related": [
    "read-quorum",
    "write-quorum",
    "sloppy-quorum",
    "linearizability"
  ],
  "citations": [
    {
      "id": "gifford",
      "title": "David K. Gifford. Weighted Voting for Replicated Data, SOSP 1979, sections 1 and 3.",
      "url": "https://www.cs.sfu.ca/~vaughan/teaching/401/papers/gifford79.pdf",
      "accessed": "2026-10-13"
    },
    {
      "id": "guarantees",
      "title": "Apache Cassandra 5.0.0: Guarantees, including lightweight transactions.",
      "url": "https://raw.githubusercontent.com/apache/cassandra/cassandra-5.0.0/doc/modules/cassandra/pages/architecture/guarantees.adoc",
      "accessed": "2026-10-13"
    },
    {
      "id": "hesela-repair",
      "title": "Replica repair: what has actually converged?",
      "url": "https://hesela.com/analyses/replica-repair-coverage/",
      "accessed": "2026-10-13"
    }
  ],
  "status": "shipping",
  "advantages": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-13"
}