{
  "slug": "pbs-k-staleness",
  "term": "PBS k-staleness",
  "aliases": [
    "Probabilistically bounded version staleness"
  ],
  "definition": "PBS k-staleness describes a probabilistic guarantee that a read includes a version from the k latest completed writes or a newer in-flight write.",
  "note": "The 2012 formulation uses version count, not elapsed time; k=1 targets the latest completed version or a newer write. Its non-expanding uniform independent-placement model raises a single-write miss probability to k. [pbs-2012]\n\nThe 2014 paper expresses version freshness using (K,p)-regular semantics, distinct from atomic semantics. A per-read freshness probability does not by itself establish a linearizable history. [pbs-2014]\n\nIn Hesela's exact constructed mixture, K is chosen independently of replica placement. Equal mean K does not imply equal miss risk: the mixture averages conditional probabilities, not exponents. This is a deduction under stated assumptions, not a workload measurement. [hesela-mixture]",
  "related": [
    "partial-quorum",
    "pbs-t-visibility",
    "monotonic-reads",
    "regular-register"
  ],
  "citations": [
    {
      "id": "pbs-2012",
      "title": "Bailis et al. Probabilistically Bounded Staleness for Practical Partial Quorums. PVLDB 5(8), 776-787 (2012), sections 3.1-3.4. DOI: 10.14778/2212351.2212359.",
      "url": "https://www.vldb.org/pvldb/vol5/p776_peterbailis_vldb2012.pdf",
      "accessed": "2026-11-11"
    },
    {
      "id": "pbs-2014",
      "title": "Bailis et al. Quantifying eventual consistency with PBS. The VLDB Journal 23, 279-302 (2014), sections 2.2-2.3, 4.1-4.2. DOI: 10.1007/s00778-013-0330-1.",
      "url": "https://www.bailis.org/papers/pbs-vldbj2014.pdf",
      "accessed": "2026-11-11"
    },
    {
      "id": "hesela-mixture",
      "title": "Hesela: exact version-count mixtures, assumptions and executable source hashes.",
      "url": "https://hesela.dev/research/pbs-count-mixtures.json",
      "accessed": "2026-11-11"
    }
  ],
  "status": "research",
  "advantages": [],
  "limitations": [
    {
      "text": "The probability depends on a stated model; no particular production failure rate or deterministic bound is implied.",
      "citationIds": [
        "pbs-2012",
        "pbs-2014"
      ]
    }
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-11"
}