feat: inline encoding for Python aggregate and window UDFs (2/4)#1545
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feat: inline encoding for Python aggregate and window UDFs (2/4)#1545timsaucer wants to merge 2 commits into
timsaucer wants to merge 2 commits into
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Adds Python-aware encoding to PythonLogicalCodec/PythonPhysicalCodec so a ScalarUDF defined in Python travels inside the serialized expression (cloudpickled into fun_definition) instead of needing a matching registration on the receiver. With that in place, Expr gains __reduce__ + classmethod from_bytes(buf, ctx=None) so pickle.dumps / pickle.loads work end-to-end on expressions built from col, lit, built-in functions, and Python scalar UDFs. Wire format is framed as <DFPYUDF magic, version byte, cloudpickle tuple>; the version byte lets a too-new/too-old payload surface a clean Execution error instead of an opaque cloudpickle unpack failure. Schema serde is via arrow-rs's native IPC (no pyarrow round-trip). Cloudpickle module handle is cached per-interpreter through PyOnceLock. Worker-side context resolution lives in a new datafusion.ipc module: set_worker_ctx / get_worker_ctx / clear_worker_ctx plus a private _resolve_ctx helper consulted by Expr.from_bytes. Priority is explicit ctx > worker ctx > global SessionContext. FFI UDFs still travel by name and require the matching registration on the receiver's context. Aggregate and window UDF inline encoding, the per-session with_python_udf_inlining toggle, sender-side context, and the user-guide docs land in follow-on PRs. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
Extends the PythonLogicalCodec / PythonPhysicalCodec inline encoding
introduced for scalar UDFs to also cover Python-defined aggregate and
window UDFs. The cloudpickle tuple shape per family is:
DFPYUDA (agg) (name, accumulator_factory, input_schema_bytes,
return_schema_bytes, state_schema_bytes,
volatility_str)
DFPYUDW (window) (name, evaluator_factory, input_schema_bytes,
return_schema_bytes, volatility_str)
Same wire-framing as scalar (family magic + version byte + cloudpickle
blob), same schema serde (arrow-rs native IPC), same cached cloudpickle
handle. The agg state schema is encoded as a full IPC schema so the
post-decode UDF reports the same names + nullability + metadata as the
sender — relevant for accumulators whose StateFieldsArgs consumers key
off names rather than positional DataType.
Required restructuring two existing UDF impls so the codec can grab
the Python callable directly:
* udaf.rs: replaces create_udaf + AccumulatorFactoryFunction closure
with a named PythonFunctionAggregateUDF that stores the Py<PyAny>
accumulator factory. Synthesizes state_{i} field names when the
Python constructor passes only Vec<DataType>; from_parts preserves
the full state schema on the decode side.
* udwf.rs: renames MultiColumnWindowUDF -> PythonFunctionWindowUDF,
drops the PartitionEvaluatorFactory PtrEq wrapper, stores the
Py<PyAny> evaluator directly. PartialEq and Hash get the same
pointer-identity fast path + debug-log exception handling already
on PythonFunctionScalarUDF.
User-facing surface:
* AggregateUDF.name and WindowUDF.name properties (parallel to the
ScalarUDF.name shipped in PR1).
* Existing UDAF/UDWF construction paths are unchanged.
The per-session with_python_udf_inlining toggle, sender-side context,
strict refusal, and user-guide docs land in PRs 3-4 of this series.
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
This was referenced May 15, 2026
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Which issue does this PR close?
No associated issue. PR 2 of 4 stacked on #1544. The diff shown against `main` is cumulative until #1544 merges — review the commits on `pr2-agg-window-inline` directly, or wait for #1544 to merge for a clean diff.
Rationale for this change
PR 1 closed the round-trip for scalar UDFs. The same shipped-expression problem applies to Python aggregate and window UDFs: their accumulator / partition-evaluator factory is a Python callable, so a receiver that only has the UDF name cannot reconstruct one. This PR extends the inline-encoding mechanism so the natural `pickle.dumps(expr)` pattern also works for expressions referencing Python UDAFs and UDWFs.
What changes are included in this PR?
Codec extension is a straight parallel of the scalar path. New wire-format families:
The aggregate state schema is encoded as a full IPC schema (not a positional `Vec`), so the post-decode UDF reports the same names, nullability, and metadata as the sender. This matters for accumulators whose `StateFieldsArgs` consumers key off names rather than positions.
To let the codec downcast and grab the Python callable directly, two existing UDF impls are restructured:
User-facing surface:
Are there any user-facing changes?
The `MultiColumnWindowUDF` rename is a Rust-side breaking change, so adding `api change` even though no Python-facing API breaks.