alkis commented on code in PR #585: URL: https://github.com/apache/parquet-format/pull/585#discussion_r3578120501
########## LogicalTypes.md: ########## @@ -635,7 +635,173 @@ The type has two type parameters: The sort order used for `GEOGRAPHY` is undefined. When writing data, no min/max statistics should be saved for this type and if such non-compliant statistics -are found during reading, they must be ignored. +are found during reading, they must be ignored. + +### FILE + +`FILE` annotates a group that represents a reference to a range of bytes, which may +be stored inline in the value, elsewhere within the current file, or in an external file. It +is intended for use cases such as storing file inventories, manifests, and unstructured +data references (e.g., images or audio files stored in object storage). + +The annotated group may contain the following fields, identified by name case sensitively, +not by field order. Field IDs, if they exist, may also be used for projection. Every field +is optional both in the schema and in the data: a writer may omit any field from the group +definition, and any field that is present has a field repetition type of `OPTIONAL`. +A group need only define the fields it uses (for example, an inline-only group may define +just `inline`, and an external reference may define just `path`). + +| Field | Type | +|----------------|------------| +| `path` | STRING | +| `offset` | INT64 | +| `size` | INT64 | +| `content_type` | STRING | +| `checksum` | STRING | +| `inline` | BYTE_ARRAY | + +A value resolves to bytes determined by `inline` / `path` / `offset` / `size`; +`content_type` and `checksum` are metadata describing whatever is resolved. + +#### Fields + +For the descriptions below, a field is *set* when it is present in the `FILE` group +and its value is non-null (and, for string fields, non-empty). A field is *not set* +when it is absent from the group, or is present but null or empty. + +##### path + +A URI-reference as defined by RFC 3986, encoded as a Parquet STRING (e.g., `s3://bucket/file.jpg`). +The URI may be absolute or relative. No additional encoding (e.g., URI encoding) is applied on top +of the user-provided data. If `path` is not set, the value refers to the current file +(a self-reference). + +##### offset + +A byte offset indicating the start of the byte range within the referenced data. +If not set, readers must treat the value as 0. +If set and non-zero, readers must seek to this offset to retrieve the referenced data. +`offset` must be set for a self-reference (`path` not set); it is optional for an +external reference (`path` set). `offset` must not be < 0. + +##### size + +The byte length of the referenced data. Must be zero or a positive integer if set; a +value of 0 indicates empty referenced data. `size` must be set whenever `offset` is set. +It may be omitted only for a whole-file external reference (`path` set, `offset` not set), +in which case the range runs to the end of the referenced file. Because a self-reference +always sets `offset`, it always sets `size` as well. + +##### content_type + +The media type (MIME type) of the resolved bytes (e.g., `image/png`). + +##### checksum + +A self-describing integrity token for the resolved bytes, of the form +`<algorithm>:base64(<digest bytes>)`. Readers should ignore unknown +algorithms. The recognized algorithms are: + +| Algorithm | Notes | +|-----------|-----------------------------------------------------------------| +| `ETAG` | the object-store eTag — equality-only, not recomputable | +| `MD5` | the usual S3/HTTP eTag and Content-MD5 | +| `CRC32` | Parquet's page-checksum algorithm (gzip/zlib) | +| `CRC32C` | common in object stores, hardware-accelerated | +| `SHA-256` | e.g. S3 additional checksums | + +`checksum` applies to the resolved bytes, except for `ETAG`, which is the +object-store eTag for the whole file referenced by `path`. Review Comment: Good point @rdblue. Perhaps we can switch to hex if it is more familiar? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
