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Move FoR serde logic from VTable to Plugin - #10104
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Signed-off-by: Matt Katz <mhkatz97@gmail.com>
Signed-off-by: Matt Katz <mhkatz97@gmail.com>
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Stacked on #10104. ## Summary The in-memory `FoR` array now allows one reference per 1024-element chunk instead of a single global reference per array. This is supported by adding a `references` child that records each reference. Element `i` decodes as `encoded[i] + references[(offset + i) / 1024]` with wrapping arithmetic. This also requires adding an `offset` pointer. This is the position of the first element within the first chunk and only matters for sliced arrays. The wire format is unchanged. `fastlanes.for` reads its single reference as a `ConstantArray` child, and `FoRPlugin` writes `fastlanes.for` only when the references are constant. Note that FoR encoding always uses a constant reference per array still and serialization refuses arrays that have non-constant references, so this change will not lead to breaks. ## Example ### References A 3000-row array spans three chunks, each with its own reference. `encoded` holds each value minus its chunk's reference. ```text rows 0 ─────────── 1023 │ 1024 ────────── 2047 │ 2048 ──────── 2999 references [ 1_000_000 │ 5_000_000 │ 9_000_000 ] encoded [ small values │ small values │ small values ] value[1500] = encoded[1500] + references[1500 / 1024] = encoded[1500] + references[1] = encoded[1500] + 5_000_000 ``` ### Offset Slicing is zero-copy, so a slice can start partway through a chunk. `offset` records how far into its first chunk the slice starts. ```text │◄──── chunk 0 ────►│◄──── chunk 1 ────►│◄──── chunk 2 ────►│ rows 0 1024 1500 2048 2500 3000 slice [═══════════════════) │◄ 476 ►│ slice(1500..2500): encoded = encoded.slice(1500..2500) 1000 rows references = references.slice(1..3) [5_000_000, 9_000_000] offset = 1500 % 1024 476 slice row i uses references[(476 + i) / 1024]: i = 0..=547 → references[0] = 5_000_000 (original chunk 1) i = 548..=999 → references[1] = 9_000_000 (original chunk 2) ``` The new offset is always below 1024. Slicing a slice adds the offsets and slices the references again. ### Constant references (existing files) ```text fastlanes.for on disk metadata = reference 42, children = [encoded] │ read ▲ write (only when references are constant) ▼ │ in memory references = ConstantArray(42, len = num_chunks), offset = 0 ``` ## API - `FoRSlots` gains `references`. - `FoRData` holds only `offset: u16`. The stored reference scalar is gone. - `FoRArrayExt::reference_scalar() -> &Scalar` is replaced by `constant_reference() -> Option<Scalar>`, which is `Some` when `references` is a `ConstantArray`. `offset()` and `ptype()` move onto the extension trait. - `FoR::try_new(encoded, reference)` keeps its signature and builds the constant child. `FoR::try_new_chunked(encoded, references, offset)` accepts any references. ## Kernels With constant references, every kernel takes its existing path. That includes Eq/NotEq compare pushdown, is_constant, is_sorted, take, filter, the fused BitPacked decode, and CUDA FFOR and dynamic dispatch. With varying references: - Decoding adds each chunk's reference in place. `scalar_at` looks up the element's chunk reference. `slice` slices the references by chunk and carries the new offset. `cast` casts the references. - Compare, is_constant, is_sorted, take and filter return `None` and fall back to decoding. - CUDA decodes these arrays on the CPU and never fuses them into a dispatch plan. Callers that rewrap a FoR's encoded child (the btrblocks FoR scheme, benches, CUDA tests) now pass through `references()` and `offset()` via `try_new_chunked`. --------- Signed-off-by: Matt Katz <mhkatz97@gmail.com>
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First PR of a stack prototyping a FoR encoding with one reference per 1024-element chunk, following the plugin approach used for
DecimalBytePartsand #9937.Summary
Move metadata, serialization and deserialization of
fastlanes.forinto a newFoRPlugin. The VTable keeps only the required serde methods, which now return an error, plus in-memory validation.vortex_fastlanes::initializeregistersFoRPlugininstead of the vtable-derived plugin.The wire format is unchanged: the metadata is still just the reference
ScalarValueproto bytes, with a singleencodedchild.Users who register
FoRdirectly on a session must now registerFoRPluginto get serde.