emkornfield commented on code in PR #186: URL: https://github.com/apache/parquet-site/pull/186#discussion_r3365940662
########## content/en/docs/File Format/versions.md: ########## @@ -0,0 +1,258 @@ +--- +title: "Parquet format versions" +linkTitle: "Versions" +weight: 9 +--- + +This page describes how features are added to the [Parquet format +specification](https://github.com/apache/parquet-format) and how they affect +reader and writer compatibility. See the +[Implementation status](../implementationstatus/) page for which implementations +(arrow, parquet-java, arrow-rs, etc.) support each feature. + +*Note*: If you find out-of-date information, please open an issue or pull request. + +## Backwards compatible features + +Backwards compatible features can still be **read by older readers**, though with +a degraded experience: they ignore the new information rather than failing. +Examples: + +* **Bloom filters**: a reader that does not understand them ignores the pruning + metadata but still reads the data correctly. +* **Logical type annotations** such as `VARIANT`: an older reader still reads the + underlying physical column (e.g. `BYTE_ARRAY`) as raw bytes, but does not apply + the logical type. + +## Backwards incompatible features + +Backwards incompatible features make the data **unreadable** to older software +that does not support them. Examples: + +* **New encodings** (e.g. the `DELTA_*` encodings, `BYTE_STREAM_SPLIT`, + `RLE_DICTIONARY`): a reader that does not implement them cannot decode the + column values. +* **Data Page V2 headers**: a reader that only understands `DataPageHeader` + cannot parse `DataPageHeaderV2` pages. + +## `FileMetadata` version field + +Each Parquet file has a `version` field in the [`thrift FileMetadata`] that +declares which features the file may use, and thus what a reader **must** support +to read it. + +**Note**: Many writers set the version field to `1` even for files that use +format 2.0 features, which has caused [confusion and interoperability +issues][closing-out-2.0]. + +## `parquet-format` release versions + +The Thrift definition is released independently of implementations such as +parquet-java or arrow-rs, following the Apache release process and +[semantic versioning]: + +1. The major version corresponds to the [`thrift FileMetadata`] `version` field. +2. Minor releases (e.g. `2.10.0` to `2.11.0`) may add backwards compatible + features, but never breaking ones. The minor version is not recorded in the + file itself. + +## Adding new features + +New features are added by discussion and voting on the [parquet dev mailing list] +(full process [here]). Once approved, a feature is added to the spec and ships in +the next parquet-format release. + +[parquet dev mailing list]: https://lists.apache.org/[email protected] +[semantic versioning]: https://semver.org/ +[`thrift FileMetadata`]: https://github.com/apache/parquet-format/blob/c42c2cb4ecfccb38153375e24b702a82fd763cc0/src/main/thrift/parquet.thrift#L1365-L1373 +[here]: https://github.com/apache/parquet-format/blob/master/CONTRIBUTING.md#additionschanges-to-the-format +[closing-out-2.0]: https://lists.apache.org/thread/0bdyyb7qobrxx94x8v7t5z7g2ksnpyr2 + +## Backwards incompatible features by version + +Backwards incompatible features and the format version each became available in: + +* **V1**: the original Parquet format (1.0). +* **V2**: format version 2.0. + +| Feature | V1 | V2 | Released in | Source | Notes | Review Comment: This also means one more page necessary to update when we add something new? -- 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]
