alamb commented on code in PR #186: URL: https://github.com/apache/parquet-site/pull/186#discussion_r3364488490
########## 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 + +*Note*: If you find out-of-date information, please open an issue or pull request.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 | +| ------------------------------------------ | ---- | ---- | ----------------------------- | --- | ------------------------- | +| [BOOLEAN] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [INT32] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [INT64] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [INT96 (deprecated)] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [FLOAT] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [DOUBLE] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [BYTE_ARRAY] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [FIXED_LEN_BYTE_ARRAY] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [Data Page V1] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [Data Page V2] | | ✅ | [2.0.0] | [1.0.0..2.0.0] | | +| [PLAIN] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [PLAIN_DICTIONARY] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [RLE] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [BIT_PACKED (deprecated)] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [RLE_DICTIONARY] | | ✅ | [2.0.0] | [1.0.0..2.0.0] | | +| [DELTA_BINARY_PACKED] | | ✅ | [2.0.0] | [1.0.0..2.0.0] | | +| [DELTA_LENGTH_BYTE_ARRAY] | | ✅ | [2.0.0] | [1.0.0..2.0.0] | | +| [DELTA_BYTE_ARRAY] | | ✅ | [2.0.0] | [1.0.0..2.0.0] | | +| [BYTE_STREAM_SPLIT] | | ✅ | [2.8.0] | [2.7.0..2.8.0] | [Approved 2019-12-03] | +| [BYTE_STREAM_SPLIT<br/>(Additional Types)] | | ✅ | [2.11.0] | [2.10.0..2.11.0] | [Approved 2024-03-18] | +| [UNCOMPRESSED] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [SNAPPY] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [GZIP] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [LZO] | ✅ | ✅ | [1.0.0] | [1.0.0][tree-1.0.0] | | +| [BROTLI] | | ✅ | [2.4.0] | [2.3.1..2.4.0] | | +| [LZ4 (deprecated)] | | ✅ | [2.4.0] | [2.3.1..2.4.0] | | +| [LZ4_RAW] | | ✅ | [2.9.0] | [2.8.0..2.9.0] | | +| [ZSTD] | | ✅ | [2.4.0] | [2.3.1..2.4.0] | | +| [Modular encryption] | | ✅ | [2.7.0] | [2.6.0..2.7.0] | [Approved 2019-01-16] | + + +> **Note:** Compression codecs and modular encryption are not gated by the +> `version` field — a reader needs support for the specific codec or for +> encryption regardless of version. + +## Backwards compatible additions + +Files written with these features can be read by all readers, but older +readers may not understand the new information. + +| Feature | Released in | Source | Notes | +| ------------------------------------------- | ----------------------------- | --- | ------------------------- | Review Comment: > Also from my own notes: > > * Addition of the LogicalType union in favor of ConvertedType enum was in 2.4.0. > * Formal deprecation of ConvertedType in 2.9.0 > * Addition of NANOS to TimeUnit 2.6.0 Good call -- added rows for these two: > * Addition of the LogicalType union in favor of ConvertedType enum was in 2.4.0. > * Addition of NANOS to TimeUnit 2.6.0 I added this as a note instead of a new row, as it doesn't change what is actually written into files, instead I think it signals a future incompatible change (no longer write converted type) > * Formal deprecation of ConvertedType in 2.9.0 -- This is an automated message from the Apache Git Service. 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