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Export decimal Widen arrays to Arrow with one copy - #10994
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Tracking Issue: #10701 Based on `develop`, including the writer work previously in #11002. #11003 and #10994 build on it. No release gate. ## Summary Canonical decimal width follows precision, so small values under `Decimal(38, 2)` still occupy 16 bytes each. A decimal `Widen` keeps those values in a lower-precision child while retaining the column's logical dtype. ## Changes The child precision must hold every valid value and have a narrower canonical width. Execution restores the logical width. Until the later kernels land, operations use that canonical fallback. Serialization writes a concrete decimal leaf through the existing `vortex.decimal` wire form without executing values or validity. Integer `Widen` arrays, non-decimal leaves, and nonserializable validity require explicit preparation by the caller. Its metadata stores the width, while the containing format supplies the parent precision. This keeps an `i32` child at four bytes per value, including IPC and writes without a compressor. A serialized-byte regression test checks that size independently of the eventual read encoding. <details> <summary>Historical local benchmark results</summary> These retained measurements predate this style pass and rebase. They do not measure the current head. `cargo bench -p vortex-array --bench widen_decimal`, Apple M4, medians. The numbers were measured at the top of this stack before the split, so they cover the whole stack, not this layer alone. The baseline is the canonical input, and the candidate is the same values as a `Widen` (child precision 5 under precision 10, 9 under 18, and 18 under 38). CodSpeed on this PR measures the layer itself. | bench | p10 canonical | p10 Widen | p18 canonical | p18 Widen | p38 canonical | p38 Widen | | --- | ---: | ---: | ---: | ---: | ---: | ---: | | `filter` | 22.16 µs | 5.083 µs | 13.66 µs | 4.916 µs | 10.58 µs | 24.74 µs | | `execute` | 10.59 ns | 2.832 µs | 10.26 ns | 2.926 µs | 10.34 ns | 9.895 µs | `execute` on a `Widen` is the widening copy, which the canonical input does not need. The canonical `filter` medians at p10 and p18 were bimodal across runs, and `filter` at p38 is slower on the `Widen`. </details> ## API Changes `WidenArray::try_new` accepts decimal children. Adds `WidenArray::encode_decimal` and registers a writer-only `WidenPlugin`, whose only write ID is `vortex.decimal`. ## Validation Source review and rebase range-diffs only. No local tests, builds, linting, or documentation checks were run. A commit hook flagged one formatting wrap, corrected manually without rerunning the check. --------- Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>
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Export the narrower decimal child directly with the logical precision and scale, avoiding the intermediate canonical-width copy. Skip null payloads when narrowing while still rejecting valid values outside the Arrow width. Keep decimal export coverage in a separate test module. Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>
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Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>
Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>
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Tracking Issue: #10701
Summary
Executing a narrow decimal
Widento its canonical width before Arrow export can copy the values twice. Exporting its child directly avoids the intermediate copy while preserving the logical precision and scale, including in nested arrays.Changes
Decimal export converts the child's buffer directly to the requested Arrow width. Narrowing skips null payloads, which can contain values too large for that width, and still rejects valid values that do not fit. Tests cover decimal widths, logical precision, nulls, slicing, and nested exports.
API Changes
No public API changes. Decimal export no longer fails solely because a null payload does not fit the Arrow width.
Validation: reviewed the source and confirmed the rebase preserves the Arrow export files. The commit hook ran Rust and TOML formatting checks successfully during the history rewrite. Tests, Clippy, and benchmarks were not run.