zstd-window-size · shipping · also Zstandard Window_Size, zstd decoding window

Zstandard window size

Zstandard window size is a frame parameter that bounds references into previously decoded frame data and determines decoding-history requirements.

Header: An ordinary frame encodes Window_Size through a window descriptor. In a single-segment frame, the descriptor is absent and Window_Size equals Frame_Content_Size. Window size in bytes is distinct from the logarithmic windowLog setting. [1]

Scope: The window is not a limit on total decoded output. A stream can contain many blocks or concatenate frames while requiring only bounded decoding history. [1]

API boundary: In the pinned library API, ZSTD_d_windowLogMax limits streaming-window allocation and does not apply to single-pass decompression. It is not an exact process-wide memory ceiling. The separate CLI probe accepted 2 MiB and 4 MiB outputs under -M1MiB with small windows. [2] [3]

Relations

related
Zstandard, Decompression bomb, Compression dictionary, Skippable frame

Citations

  1. RFC 8878: frames and Window Descriptor, sections 3.1 and 3.1.1.1.2 (accessed 2026-10-17)
  2. Zstandard v1.5.7 API manual: frame content size and ZSTD_d_windowLogMax (accessed 2026-10-17)
  3. Hesela: Zstandard decoder windows versus decoded-output budgets (accessed 2026-10-17)
Sources & caveats
  • General file-format and v1.5.7 API scope; no HTTP content-coding limits are inferred.
  • CLI measurements use Zstandard 1.5.5 with synthetic data and do not measure resident memory or direct API calls.

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Hesela team. Zstandard window size. Hesela. 2026-10-17. https://hesela.dev/terms/zstd-window-size/