compression-dictionary · shipping · also External compression dictionary

Compression dictionary

A compression dictionary supplies reusable prior content or coding state that an encoder and decoder use to represent data more compactly.

Related Observatory article: Compression dictionary on hesela.com

Zstandard accepts raw-content and formatted dictionaries. A zero result from ZSTD_getDictID_fromFrame can mean no dependency, an omitted identifier, insufficient header bytes or invalid input; it is not proof that a dictionary is unnecessary. [1]

A measured raw-dictionary example decoded to incorrect bytes with a successful exit when the wrong dictionary was supplied and the content checksum was absent. The checked version rejected that mismatch. Preserving dictionary identity is part of the restore contract. [2]

A separate formatted-dictionary experiment retained ID 123456 while changing one content byte. With no verified checksum, decoding succeeded with wrong bytes; changing only the ID instead triggered an ID mismatch. A numeric ID is a selection check, not a digest of the dictionary. [2]

Relations

related

zstandard, backup-manifest, restore-test, cryptographic-hash, zstandard-dictionary-id

Citations

1. Zstandard v1.5.7 API manual: dictionary identification and decompression (accessed 2026-10-17)
2. Hesela: Compressed archives, dictionary dependencies and validation coverage (accessed 2026-10-17)

JSON: /data/terms/compression-dictionary.json