{
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20",
  "slug": "external-synchrony",
  "term": "External synchrony",
  "aliases": [
    "externally synchronous I/O"
  ],
  "definition": "External synchrony delays causally dependent external output until the underlying file modifications are durable, while allowing internal execution to continue.",
  "note": "The xsyncfs research prototype propagates commit dependencies through local communication. A syscall return is not the external observation boundary. Late media failures complicate application-specific recovery; this is not a generic guarantee of asynchronous I/O. [external-synchrony]",
  "related": [
    "persistence-ordering",
    "crash-consistency",
    "optimistic-crash-consistency"
  ],
  "citations": [
    {
      "id": "external-synchrony",
      "title": "Nightingale, Veeraraghavan, Chen and Flinn. Rethink the Sync. OSDI 2006, pp. 1-14.",
      "url": "https://static.usenix.org/events/osdi06/tech/nightingale/nightingale_html/index.html",
      "accessed": "2026-10-20"
    }
  ]
}