{
  "slug": "hyperbolic-caching",
  "term": "Hyperbolic caching",
  "aliases": [
    "Hyperbolic cache replacement"
  ],
  "definition": "Hyperbolic caching is a replacement policy that estimates an object's frequency over its current cache residence and evaluates sampled eviction candidates lazily.",
  "note": "The base score is access count divided by time since insertion, not time since the last hit. Insertion starts the count at one; eviction discards this residence history. The lowest current score among sampled candidates is selected, not necessarily the global minimum. [paper]\n\nConstructed example: A has four accesses since time 0; B has one since time 9. With no further accesses to either, their scores at time 10 are 2/5 and 1; at time 12 both are 1/3; at time 20 they are 1/5 and 1/11. The lower-priority object changes from A to B. These are exact arithmetic results, not measured cache performance. [example]\n\nFor 100 residents, a fixed lowest-priority set of ten and eight independent uniform draws with replacement, the chance of sampling at least one of those ten is 1 - (9/10)^8 = 56.953279%. This is neither the chance of selecting the unique global minimum nor a hit-rate prediction. [example]\n\nThe author simulator's ordinary Sampling.sample path uses integer draws that permit repeated candidates. Retained-candidate and other sampling variants require their own probability model. [artifact]",
  "status": "research",
  "advantages": [],
  "limitations": [],
  "related": [
    "lrfu",
    "cache-admission",
    "greedydual-size",
    "sieve-eviction"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-12",
  "citations": [
    {
      "id": "paper",
      "title": "Blankstein, Sen and Freedman. Hyperbolic Caching: Flexible Caching for Web Applications. USENIX ATC 2017, pp. 499-511, sections 2.1 and 2.4, Figure 1.",
      "url": "https://www.usenix.org/system/files/conference/atc17/atc17-blankstein.pdf",
      "accessed": "2026-11-12"
    },
    {
      "id": "artifact",
      "title": "Author simulator: Sampling.sample, commit 884c466c311bb5b9fbdd09791d829b04032f3947.",
      "url": "https://github.com/kantai/hyperbolic-caching/blob/884c466c311bb5b9fbdd09791d829b04032f3947/simulation/strategies/sampling.py",
      "accessed": "2026-11-12"
    },
    {
      "id": "example",
      "title": "Hesela: exact priority-crossing and sampling calculations.",
      "url": "https://hesela.dev/research/hyperbolic/results.json",
      "accessed": "2026-11-12"
    },
    {
      "id": "code",
      "title": "Hesela: standalone reference arithmetic and input validation.",
      "url": "https://hesela.dev/research/hyperbolic/model.py",
      "accessed": "2026-11-12"
    }
  ],
  "provenance": [
    "Primary-paper and pinned-source review; no execution of the historical author simulator.",
    "Equal-size, equal-cost resident objects; positive residence ages only. The reference calculation rejects zero age rather than specifying a production tie or timestamp policy."
  ]
}