Add new Avro files for decimal data types #112
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jecsand838
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alamb
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Sep 8, 2025
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Thank you @jecsand838 -- this makes sense to me
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This PR now sadly has a conflict |
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# Which issue does this PR close? - Part of #4886 # Rationale for this change Apache Avro’s `decimal` logical type annotates either `bytes` or `fixed` and carries `precision` and `scale`. Implementations should reject invalid combinations such as `scale > precision`, and the underlying bytes are the two’s‑complement big‑endian representation of the unscaled integer. On the Arrow side, Rust now exposes first‑class `Decimal32`, `Decimal64`, `Decimal128`, and `Decimal256` data types with documented maximum precisions (9, 18, 38, 76 respectively). Until now, `arrow-avro` decoded all Avro decimals to 128/256‑bit Arrow decimals, even when a narrower type would suffice. # What changes are included in this PR? **`arrow-avro/src/codec.rs`** * Map `Codec::Decimal(precision, scale, _size)` to Arrow’s `Decimal32`/`64`/`128`/`256` **by precision**, preferring the narrowest type (≤9→32, ≤18→64, ≤38→128, otherwise 256). * Strengthen decimal attribute parsing: * Error if `scale > precision`. * Error if `precision` exceeds Arrow’s maximum (Decimal256). * If Avro uses `fixed`, check that declared `precision` fits the byte width (≤4→max 9, ≤8→18, ≤16→38, ≤32→76). * Update docstring of `Codec::Decimal` to mention `Decimal32`/`64`. **`arrow-avro/src/reader/record.rs`** * Add `Decoder::Decimal32` and `Decoder::Decimal64` variants with corresponding builders (`Decimal32Builder`, `Decimal64Builder`). * Builder selection: * If Avro uses **fixed**: choose by size (≤4→Decimal32, ≤8→Decimal64, ≤16→Decimal128, ≤32→Decimal256). * If Avro uses **bytes**: choose by declared precision (≤9/≤18/≤38/≤76). * Implement decode paths that sign‑extend Avro’s two’s‑complement payload to 4/8 bytes and append values to the new builders; update `append_null`/`flush` for 32/64‑bit decimals. **`arrow-avro/src/reader/mod.rs` (tests)** * Expand `test_decimal` to assert that: * bytes‑backed decimals with precision 4 map to `Decimal32`; precision 10 map to `Decimal64`; * legacy fixed\[8] decimals map to `Decimal64`; * fixed\[16] decimals map to `Decimal128`. * Add a nulls path test for bytes‑backed `Decimal32`. # Are these changes tested? Yes. Unit tests under `arrow-avro/src/reader/mod.rs` construct expected `Decimal32Array`/`Decimal64Array`/`Decimal128Array` with `with_precision_and_scale`, and compare against batches decoded from Avro files (including legacy fixed and bytes‑backed cases). The tests also exercise small batch sizes to cover buffering paths; a new Avro data file is added for higher‑width decimals. New Avro test file details: - test/data/int256_decimal.avro # bytes logicalType: decimal(precision=76, scale=10) - test/data/fixed256_decimal.avro # fixed[32] logicalType: decimal(precision=76, scale=10) - test/data/fixed_length_decimal_legacy_32.avro # fixed[4] logicalType: decimal(precision=9, scale=2) - test/data/int128_decimal.avro # bytes logicalType: decimal(precision=38, scale=2) These new Avro test files were created using this script: https://gist.github.com/jecsand838/3890349bdb33082a3e8fdcae3257eef7 There is also an arrow-testing PR for these new files: apache/arrow-testing#112 # Are there any user-facing changes? N/A due to `arrow-avro` not being public.
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Thanks @jecsand838 |
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This adds new fixed256_decimal.avro, fixed_length_decimal_legacy_32.avro, int128_decimal.avro, int256_decimal.avro files which will be used to test
arrow-avro.Here's the python script used to generate the new Avro file: https://gist.github.com/3890349bdb33082a3e8fdcae3257eef7.git
Part of apache/arrow-rs#4886