{
  "slug": "speculative-partial-write",
  "term": "Speculative partial write",
  "aliases": [
    "PARIX"
  ],
  "definition": "A speculative partial write in PARIX logs a replacement value and requests the original only when the parity journal lacks the required baseline.",
  "note": "The retained baseline applies within a journal epoch, not forever. PARIX is a research prototype, not a Linux MD mode. Its published IOPS comparison excludes background log flushing.",
  "status": "research",
  "advantages": [
    "Repeated overwrites within an epoch can avoid old-data reads"
  ],
  "limitations": [
    "Replay resets the baseline",
    "The first write can require an additional exchange and original-value log record"
  ],
  "related": [
    "parity-logging",
    "read-modify-write",
    "partial-parity-log"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-19",
  "citations": [
    {
      "id": "parix2017",
      "title": "Li et al. PARIX: Speculative Partial Writes in Erasure-Coded Systems. USENIX ATC 2017, sections 3-5.",
      "url": "https://www.usenix.org/system/files/conference/atc17/atc17-li_huiba.pdf",
      "accessed": "2026-10-19"
    },
    {
      "id": "hesela",
      "title": "Hesela: RAID write accounting and parity replay traces",
      "url": "https://hesela.com/analyses/raid-write-penalty-io-not-speed/#parity-logging",
      "accessed": "2026-10-19"
    }
  ]
}