{
  "slug": "phi-accrual-detector",
  "term": "Phi accrual failure detector",
  "aliases": [
    "phi failure detector",
    "phi accrual detector"
  ],
  "definition": "A phi accrual failure detector expresses suspicion as the negative base-10 logarithm of an estimated heartbeat inter-arrival tail probability.",
  "note": "A threshold converts the score into an action; the score is not a posterior probability of node failure. Its meaning depends on the arrival model. [phi-report] [hesela-phi]\n\nCassandra 5.0.0 scales elapsed time divided by the sampled mean by 1/ln(10) for threshold comparisons and JMX reporting. This differs from the original normal-tail implementation. Seeding, filtering and pause handling also affect behavior. [cassandra-500]",
  "related": [
    "failure-detector",
    "interarrival-time",
    "gray-failure",
    "io-fencing"
  ],
  "citations": [
    {
      "id": "phi-report",
      "title": "Hayashibara, Defago, Yared and Katayama, The phi accrual failure detector, JAIST IS-RR-2004-010 (10 May 2004), sections IV-V.",
      "url": "https://dspace.jaist.ac.jp/dspace/handle/10119/4784",
      "accessed": "2026-10-17"
    },
    {
      "id": "cassandra-500",
      "title": "Apache Cassandra 5.0.0: FailureDetector.java, ArrivalWindow.phi, interpret and getPhiValues.",
      "url": "https://github.com/apache/cassandra/blob/cassandra-5.0.0/src/java/org/apache/cassandra/gms/FailureDetector.java",
      "accessed": "2026-10-17"
    },
    {
      "id": "hesela-phi",
      "title": "Phi failure detectors: suspicion is not a failure probability",
      "url": "https://hesela.com/analyses/phi-failure-detectors-suspicion/",
      "accessed": "2026-10-17"
    }
  ],
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-17"
}