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The SOCI project introduces several new terms that sometimes have subtle differences between them. This glossary defines these terms.

Terminology

  • SOCI: Seekable OCI (pronounced so-CHEE). SOCI combines an unmodified OCI Image (or Docker v2 image) with a SOCI index to enable the SOCI snapshotter to lazily pull the image at runtime.

  • SOCI index: An OCI artifact consisting of a SOCI index manifest and a set of zTOCs that enable lazy loading of unmodified OCI images. "Index" refers to the whole set of objects similarly to how "image" refers to the set of image index, manifest, config, and layers.

  • SOCI index manifest: An OCI Artifact manifest containing the list of zTOCs in the SOCI Index as well as a reference to the image for which the manifest was generated.

  • zTOC: A Table of Contents for compressed data. A zTOC is composed of 2 parts. 1) a table of contents containing file metadata and its offset in the decompressed TAR archive (the "TOC"). 2) A collection of "checkpoints" of the state of the compression engine at various points in the layer. We refer to this collection as the "zInfo".

  • span: A chunk of data that can be independently decompressed. Each checkpoint in the zInfo corresponds to exactly one span in an image layer.

Anti-terminology

  • SOCI Image: We generally avoid the term "SOCI Image" because there is no such thing! The image is an unmodified OCI image. Also, a single image may have many SOCI indices with different parameters such as span size, layers indexed, etc. The precise way to refer to an image that has a SOCI index is to refer to the index itself.