Replace prefetch_file_metadata's bool/Unspecified with explicit remote_only/always/never

python/cudf_polars/cudf_polars/dsl/utils/io.py

@@ -28,8 +28,8 @@ class CachedParquetInfo:
     Metadata for a parquet file.
 
     File metadata is only cached when the setting
-    ``ParquetOptions.prefetch_file_metadata`` is ``True``. Metadata is cached
-    for the duration of the query.
+    ``ParquetOptions.prefetch_file_metadata`` is not ``"never"``. Metadata is
+    cached for the duration of the query.
 
     Parameters
     ----------

python/cudf_polars/cudf_polars/engine/core.py

@@ -42,7 +42,7 @@
 from cudf_polars.streaming.parallel import lower_ir_graph_with_node_map
 from cudf_polars.streaming.statistics import collect_statistics
 from cudf_polars.streaming.utils import _concat
-from cudf_polars.utils.config import Unspecified, get_total_device_memory
+from cudf_polars.utils.config import get_total_device_memory
 
 if TYPE_CHECKING:
     from collections.abc import Callable, MutableMapping
@@ -786,12 +786,12 @@ def evaluate_on_rank(
     )
 
     prefetch_file_metadata = config_options.parquet_options.prefetch_file_metadata
-    if prefetch_file_metadata is not False:
+    if prefetch_file_metadata != "never":
         cached_parquet_info_map = prefetch_parquet_file_metadata_for_ir(
             ir,
             ir_context.py_executor,
             stats=stats,
-            remote_only=isinstance(prefetch_file_metadata, Unspecified),
+            remote_only=prefetch_file_metadata == "remote_only",
         )
         attach_cached_parquet_metadata(ir, cached_parquet_info_map)
 

python/cudf_polars/cudf_polars/streaming/benchmarks/utils.py

@@ -689,9 +689,7 @@ def serialize(self, engine: StreamingEngine | None) -> dict:
             config_options = config_options.drop_unserializable()
             rapidsmpf_options = engine.rapidsmpf_options.get_strings()
             result["config_options"] = {
-                "config_options": dataclasses.asdict(
-                    config_options, dict_factory=ConfigOptions.dict_factory
-                ),
+                "config_options": dataclasses.asdict(config_options),
                 "rapidsmpf_options": rapidsmpf_options,
             }
             # discard unserializable / unnecessary UUIDs

python/cudf_polars/cudf_polars/streaming/select.py

@@ -440,7 +440,7 @@ def _(
             scan_child.skip_rows,
             scan_child.n_rows,
             dataclasses.replace(
-                scan_child.parquet_options, prefetch_file_metadata=False
+                scan_child.parquet_options, prefetch_file_metadata="never"
             ),
             None,
         )

python/cudf_polars/cudf_polars/utils/config.py

@@ -70,11 +70,9 @@ class Unspecified:
     Sentinel value meaning "no value was explicitly provided".
 
     The singleton instance :data:`UNSPECIFIED` is used as the default for every
-    :class:`StreamingOptions` field, as well as for
-    ``ParquetOptions.prefetch_file_metadata``. When a field is still
-    ``UNSPECIFIED`` after construction (i.e. neither an explicit value nor a
-    matching environment variable was provided), the consuming component decides
-    on the semantics.
+    :class:`StreamingOptions` field. When a field is still ``UNSPECIFIED`` after
+    construction (i.e. neither an explicit value nor a matching environment
+    variable was provided), the consuming component decides on the semantics.
     """
 
     _instance: Unspecified | None = None
@@ -91,8 +89,7 @@ def __repr__(self) -> str:
 
 
 UNSPECIFIED = Unspecified()
-"""Singleton sentinel for all :class:`StreamingOptions` fields, as well as for
-``ParquetOptions.prefetch_file_metadata``.
+"""Singleton sentinel for all :class:`StreamingOptions` fields.
 
 A field set to ``UNSPECIFIED`` after construction means no explicit value and no
 matching environment variable was found; the consuming component decides on the
@@ -221,6 +218,24 @@ def _bool_converter(v: str) -> bool:
         raise ValueError(f"Invalid boolean value: '{v}'")
 
 
+PrefetchFileMetadata = Literal["remote_only", "always", "never"]
+
+
+def _prefetch_file_metadata_converter(v: str) -> PrefetchFileMetadata:
+    lowered = v.lower()
+    if lowered in {"remote_only", "always", "never"}:
+        return lowered  # type: ignore[return-value]
+    try:
+        # Also accept boolean-style values, for parity with other options:
+        # true/1 means "always", false/0 means "never".
+        return "always" if _bool_converter(v) else "never"
+    except ValueError:
+        raise ValueError(
+            f"Invalid value for prefetch_file_metadata: '{v}'. "
+            "Must be one of 'remote_only', 'always', 'never'."
+        ) from None
+
+
 def _quent_context_converter(v: str) -> QuentContext | None:
     from cudf_polars.quent._context import QuentContext
 
@@ -271,10 +286,14 @@ class ParquetOptions:
         will also be skipped if ``max_footer_samples`` is 0.
     prefetch_file_metadata
         Whether to prefetch parquet file metadata and pass it through
-        `parquet_metadatas` to avoid rereading file footers. Not supported
-        by the in-memory executor, where it defaults to disabled. For the
-        streaming executor, it defaults to being enabled for remote URIs
-        (e.g. ``s3://``) only; pass ``True`` to also prefetch local files.
+        `parquet_metadatas` to avoid rereading file footers. One of
+        ``"remote_only"``, ``"always"``, or ``"never"``. ``"remote_only"``
+        (the default) prefetches remote URIs (e.g. ``s3://``) only, and only
+        for the streaming executor. ``"always"`` prefetches local files too.
+        ``"never"`` disables prefetching. ``"always"`` is not supported by
+        the in-memory executor. The environment variable also accepts
+        boolean-style values (``"1"``/``"0"``, ``"true"``/``"false"``, etc.),
+        which map to ``"always"``/``"never"`` respectively.
     use_jit_filter
         Whether to use JIT compilation for post-read filtering in Parquet scans.
         When enabled, filter predicates are JIT-compiled to CUDA kernels for
@@ -314,11 +333,11 @@ class ParquetOptions:
             f"{_env_prefix}__MAX_ROW_GROUP_SAMPLES", int, default=1
         )
     )
-    prefetch_file_metadata: bool | Unspecified = dataclasses.field(
+    prefetch_file_metadata: PrefetchFileMetadata = dataclasses.field(
         default_factory=_make_default_factory(
             f"{_env_prefix}__PREFETCH_FILE_METADATA",
-            _bool_converter,
-            default=UNSPECIFIED,
+            _prefetch_file_metadata_converter,
+            default="remote_only",
         )
     )
     use_jit_filter: bool = dataclasses.field(
@@ -342,8 +361,10 @@ def __post_init__(self) -> None:  # noqa: D105
             raise TypeError("max_footer_samples must be an int")
         if not isinstance(self.max_row_group_samples, int):
             raise TypeError("max_row_group_samples must be an int")
-        if not isinstance(self.prefetch_file_metadata, (bool, Unspecified)):
-            raise TypeError("prefetch_file_metadata must be a bool when specified")
+        if self.prefetch_file_metadata not in {"remote_only", "always", "never"}:
+            raise TypeError(
+                "prefetch_file_metadata must be one of 'remote_only', 'always', 'never'"
+            )
         if not isinstance(self.use_jit_filter, bool):
             raise TypeError("use_jit_filter must be a bool")
 
@@ -1002,27 +1023,6 @@ class ConfigOptions(Generic[ExecutorType]):
     device: int | None = None
     memory_resource_config: MemoryResourceConfig | None = None
 
-    @staticmethod
-    def dict_factory(items: list[tuple[str, Any]]) -> dict[str, Any]:
-        """
-        ``dict_factory`` for :func:`dataclasses.asdict`.
-
-        Converts any :data:`UNSPECIFIED` value to ``None``
-        (e.g. ParquetOptions.prefetch_file_metadata) so the resulting
-        dict can be serialized with :func:`json.dumps`.
-
-        Parameters
-        ----------
-        items
-            The ``(key, value)`` pairs for a single dataclass level, as passed
-            by :func:`dataclasses.asdict`.
-
-        Returns
-        -------
-        A dict with :data:`UNSPECIFIED` values replaced by ``None``.
-        """
-        return {k: (None if isinstance(v, Unspecified) else v) for k, v in items}
-
     def drop_unserializable(self) -> ConfigOptions[ExecutorType]:
         """
         Return a copy safe to pickle to a worker/actor.
@@ -1064,7 +1064,9 @@ def from_polars_engine(
 
         # Engine-dependent default: only prefetch for the streaming executor.
         # Skipped if the user or the environment has already set a value.
-        prefetch_default = UNSPECIFIED if user_executor == "streaming" else False
+        prefetch_default: PrefetchFileMetadata = (
+            "remote_only" if user_executor == "streaming" else "never"
+        )
         prefetch_env_set = (
             os.environ.get(f"{ParquetOptions._env_prefix}__PREFETCH_FILE_METADATA")
             is not None
@@ -1080,7 +1082,7 @@ def from_polars_engine(
             parquet_options = ParquetOptions(**user_parquet_options)
         else:
             if (
-                isinstance(user_parquet_options.prefetch_file_metadata, Unspecified)
+                user_parquet_options.prefetch_file_metadata == "remote_only"
                 and not prefetch_env_set
             ):
                 user_parquet_options = dataclasses.replace(
@@ -1115,7 +1117,7 @@ def from_polars_engine(
         match user_executor:
             case "in-memory":
                 executor = InMemoryExecutor(**user_executor_options)
-                if parquet_options.prefetch_file_metadata is True:
+                if parquet_options.prefetch_file_metadata == "always":
                     raise NotImplementedError(
                         "Prefetching is not supported for the in-memory executor."
                     )

python/cudf_polars/tests/streaming/test_scan.py

@@ -105,7 +105,7 @@ def test_scan_parquet_prefetch_file_metadata(
     streaming_engine = streaming_engine_factory(
         StreamingOptions(
             target_partition_size=target_partition_size,
-            parquet_options={"prefetch_file_metadata": True},
+            parquet_options={"prefetch_file_metadata": "always"},
         ),
     )
     make_partitioned_source(df, tmp_path, "parquet", n_files=n_files)
@@ -114,7 +114,7 @@ def test_scan_parquet_prefetch_file_metadata(
 
 def test_prefetch_file_metadata_non_parquet_scan(df, streaming_engine_factory) -> None:
     streaming_engine = streaming_engine_factory(
-        StreamingOptions(parquet_options={"prefetch_file_metadata": True}),
+        StreamingOptions(parquet_options={"prefetch_file_metadata": "always"}),
     )
     assert_gpu_result_equal(df.lazy().select("x"), engine=streaming_engine)
 
@@ -153,7 +153,7 @@ def test_prefetch_file_metadata_select_fast_count(
     tmp_path: Path,
 ) -> None:
     streaming_engine = streaming_engine_factory(
-        StreamingOptions(parquet_options={"prefetch_file_metadata": True}),
+        StreamingOptions(parquet_options={"prefetch_file_metadata": "always"}),
     )
     source = tmp_path / "data.parquet"
     df.write_parquet(source)
@@ -373,7 +373,8 @@ def test_streaming_scan_raises() -> None:
 def test_scan_path_mismatch_raises() -> None:
     # This isn't reachable by polars' public API, so we test it directly.
     scan = _make_parquet_scan(
-        ["file.parquet"], parquet_options=ParquetOptions(prefetch_file_metadata=True)
+        ["file.parquet"],
+        parquet_options=ParquetOptions(prefetch_file_metadata="always"),
     )
     ctx = IRExecutionContext()
 
@@ -401,7 +402,8 @@ def test_scan_path_mismatch_raises() -> None:
 def test_streaming_scan_missing_prefetch_metadata_raises() -> None:
     # This isn't reachable by polars' public API, so we test it directly.
     scan = _make_parquet_scan(
-        ["file.parquet"], parquet_options=ParquetOptions(prefetch_file_metadata=True)
+        ["file.parquet"],
+        parquet_options=ParquetOptions(prefetch_file_metadata="always"),
     )
     fused = FusedScan(scan.schema, scan, scan.paths, scan.parquet_options, [])
 
@@ -412,7 +414,7 @@ def test_streaming_scan_missing_prefetch_metadata_raises() -> None:
 
 def test_split_scan_do_evaluate_missing_prefetch_metadata() -> None:
     paths = ["/some/missing/file.parquet"]
-    parquet_options = ParquetOptions(prefetch_file_metadata=True)
+    parquet_options = ParquetOptions(prefetch_file_metadata="always")
     context = IRExecutionContext()
     schema = {"x": DataType(pl.Int64())}
 
@@ -448,7 +450,7 @@ def test_prefetch_file_metadata_join(
     pl.DataFrame({"k": [1, 2, 3], "b": [7, 8, 9]}).write_parquet(p2)
 
     engine = streaming_engine_factory(
-        StreamingOptions(parquet_options={"prefetch_file_metadata": True}),
+        StreamingOptions(parquet_options={"prefetch_file_metadata": "always"}),
     )
 
     q = pl.scan_parquet(p1).join(pl.scan_parquet(p2), on="k")
@@ -483,7 +485,7 @@ def test_prefetch_file_metadata_with_cached_scan_parent_nodes(
     ).write_parquet(source)
 
     engine = streaming_engine_factory(
-        StreamingOptions(parquet_options={"prefetch_file_metadata": True}),
+        StreamingOptions(parquet_options={"prefetch_file_metadata": "always"}),
     )
 
     cached_scan = pl.scan_parquet(source).cache()