{
  "status": "shipping",
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20",
  "advantages": [],
  "limitations": [],
  "slug": "hdf5-global-heap",
  "term": "HDF5 global heap",
  "aliases": [
    "HDF5 global heap collection"
  ],
  "definition": "The HDF5 global heap stores file objects, including variable-length payloads, that datasets access through heap identifiers.",
  "note": "A file can contain multiple global-heap collections. They are reached through references rather than a single directory of all collections; \"global\" does not mean one contiguous region. Variable-length elements in dataset storage contain a sequence length and heap identifier instead of the complete payload. [h5-format]\n\nThis is an on-disk structure, not the process-memory heap. It is also distinct from HDF5 fractal heaps, whose uses and filtering rules must not be assumed to apply to global heaps. [h5-format]\n\nDataset filters do not process the separate variable-length payload heaps. A compressed chunk can therefore hold compressed descriptors while leaving referenced strings uncompressed. Raw chunk storage is insufficient to budget the complete file; the linked experiment compares three representations with byte-exact readback. [h5-filters] [hesela-vlen]",
  "related": [
    "hdf5",
    "hdf5-chunked-layout",
    "hdf5-raw-data-chunk-cache"
  ],
  "citations": [
    {
      "id": "h5-format",
      "title": "HDF5 File Format Specification: III.E Global Heap and IV.B Data Object Data Storage",
      "url": "https://portal.hdfgroup.org/documentation/hdf5/latest/_f_m_t4.html",
      "accessed": "2026-10-20"
    },
    {
      "id": "h5-filters",
      "title": "HDF Group: H5Pset_filter, dataset filters and heap scope",
      "url": "https://portal.hdfgroup.org/documentation/hdf5/latest/group___o_c_p_l.html",
      "accessed": "2026-10-20"
    },
    {
      "id": "hesela-vlen",
      "title": "Hesela: variable-length string storage controls and measurements",
      "url": "https://hesela.dev/datasets/hdf5-chunk-cache-reads/#variable-length",
      "accessed": "2026-10-20"
    }
  ]
}