{
  "slug": "latency-histogram-bin",
  "term": "Latency histogram bin",
  "aliases": [
    "latency bucket"
  ],
  "definition": "A latency histogram bin counts observations assigned to a defined time interval, whose representative value need not equal any individual observation.",
  "note": "Histogram precision depends on bin boundaries, not the number of digits printed for a representative. In fio JSON+, duration keys represent intervals; preserve units, latency statistic and histogram layout before combining counts. [fio-hist-manual]\n\nA quantile selected from counts belongs to the selected interval. It is not thereby an exact latency or a confidence interval for a population quantile. A threshold inside that interval may leave the number of violations unresolved. Saturating overflow bins need separate treatment because their representative does not cap the observations. [fio-hist-code]\n\nHesela supplies a constructed count example, tested arithmetic and source hashes; no hardware benchmark was run. Counts are combined without reconstructing individual samples, and integer rank comparisons avoid floating-point threshold rounding. [hesela-histogram]\n\nA separate executed fio 3.41 null-engine check reconciles 8192 per-I/O completion records with JSON+ bins across four runs. Four other runs with window-mean logging each emit two log rows while their histograms retain 2048 observations. Averaged log rows must not be treated as individual latency samples; equal millisecond timestamps also do not identify duplicate I/Os. These are reporting checks without device transfers. [hesela-log-check]",
  "related": [
    "quantile",
    "completion-latency",
    "tail-latency"
  ],
  "citations": [
    {
      "id": "fio-hist-manual",
      "title": "fio manual: JSON+ bin midpoints, log_hist_msec and log_hist_coarseness; accessed 21 October 2026.",
      "url": "https://fio.readthedocs.io/en/latest/fio_doc.html#json-output",
      "accessed": "2026-10-21"
    },
    {
      "id": "fio-hist-code",
      "title": "fio 3.41 stat.c: plat_val_to_idx, plat_idx_to_val and count-based percentile selection.",
      "url": "https://github.com/axboe/fio/blob/fio-3.41/stat.c",
      "accessed": "2026-10-21"
    },
    {
      "id": "hesela-histogram",
      "title": "Hesela: histogram precision, strict-threshold bounds and reproducible arithmetic",
      "url": "https://hesela.com/analyses/storage-latency-coordinated-omission/#histogram-resolution",
      "accessed": "2026-10-21"
    },
    {
      "id": "hesela-log-check",
      "title": "Hesela: executed fio 3.41 null-engine log/histogram reconciliation, raw evidence and replay checker",
      "url": "https://hesela.com/analyses/storage-latency-coordinated-omission/#native-log-check",
      "accessed": "2026-10-21"
    }
  ],
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-21"
}