fix(coordinate): Log warning on unsafe regional writes

src/nwp_consumer/internal/entities/coordinates.py

@@ -38,6 +38,7 @@
 import dataclasses
 import datetime as dt
 import json
+import logging
 from importlib.metadata import PackageNotFoundError, version
 
 import dask.array
@@ -54,12 +55,14 @@
 except PackageNotFoundError:
     __version__ = "v?"
 
+log = logging.getLogger("nwp-consumer")
+
 
 @dataclasses.dataclass(slots=True)
 class NWPDimensionCoordinateMap:
     """Container for dimensions names and their coordinate index values.
 
-    Each field in the container is a dimension label, and the corresponding
+    Each public field in the container is a dimension label, and the corresponding
     value is a list of the coordinate values for each index along the dimension.
 
     All NWP data has an associated init time, step, and variable,
@@ -91,12 +94,6 @@ class NWPDimensionCoordinateMap:
     """
     longitude: list[float] | None = None
     """The longitude coordinates of the forecast grid in degrees. """
-    maximum_number_of_chunks_in_one_dim: int = 8
-    """ The maximum number of chunks in one dimension.
-    When saving to S3 we might want this to be small, to reduce the number of files saved.
-
-    Will be truncated to 4 decimal places, and ordered as -180 -> 180.
-    """
 
     def __post_init__(self) -> None:
         """Rigidly set input value ordering and precision."""
@@ -119,9 +116,7 @@ def dims(self) -> list[str]:
         Ignores any dimensions that do not have a corresponding coordinate
         index value list.
         """
-        return [f.name for f in dataclasses.fields(self) if
-                getattr(self, f.name) is not None
-                and f.name != "maximum_number_of_chunks_in_one_dim"]
+        return [f.name for f in dataclasses.fields(self) if getattr(self, f.name) is not None]
 
     @property
     def shapemap(self) -> dict[str, int]:
@@ -384,6 +379,8 @@ def determine_region(
                 # TODO: of which might loop around the edges of the grid. In this case, it would
                 # TODO: be useful to determine if the run is non-contiguous only in that it wraps
                 # TODO: around that boundary, and in that case, split it and write it in two goes.
+                # TODO: 2025-01-06: I think this is a resolved problem now that fetch_init_data
+                # can return a list of DataArrays.
                 return Failure(
                     ValueError(
                         f"Coordinate values for dimension '{inner_dim_label}' do not correspond "
@@ -398,47 +395,58 @@ def determine_region(
 
         return Success(slices)
 
-    def default_chunking(self) -> dict[str, int]:
+    def chunking(self, chunk_count_overrides: dict[str, int]) -> dict[str, int]:
         """The expected chunk sizes for each dimension.
 
         A dictionary mapping of dimension labels to the size of a chunk along that
         dimension. Note that the number is chunk size, not chunk number, so a chunk
         that wants to cover the entire dimension should have a size equal to the
         dimension length.
 
-        It defaults to a single chunk per init time and step, and 8 chunks
-        for each entire other dimension. These are purposefully small, to ensure
-        that when perfomring parallel writes, chunk boundaries are not crossed.
+        It defaults to a single chunk per init time, step, and variable coordinate,
+        and 2 chunks for each entire other dimension, unless overridden by the
+        `chunk_count_overrides` argument.
+
+        The defaults are purposefully small, to ensure that when performing parallel
+        writes, chunk boundaries are not crossed.
+
+        Args:
+            chunk_count_overrides: A dictionary mapping dimension labels to the
+                number of chunks to split the dimension into.
         """
         out_dict: dict[str, int] = {
             "init_time": 1,
             "step": 1,
+            "variable": 1,
         } | {
-            dim: len(getattr(self, dim)) // self.maximum_number_of_chunks_in_one_dim
-            if len(getattr(self, dim)) > self.maximum_number_of_chunks_in_one_dim else 1
+            dim: len(getattr(self, dim)) // chunk_count_overrides.get(dim, 2)
+            if len(getattr(self, dim)) > 8 else 1
             for dim in self.dims
-            if dim not in ["init_time", "step"]
+            if dim not in ["init_time", "step", "variable"]
         }
 
         return out_dict
 
 
-    def as_zeroed_dataarray(self, name: str) -> xr.DataArray:
+    def as_zeroed_dataarray(self, name: str, chunks: dict[str, int]) -> xr.DataArray:
         """Express the coordinates as an xarray DataArray.
 
-        Data is populated with zeros and a default chunking scheme is applied.
+        The underlying dask array is a zeroed array with the shape of the dataset,
+        that is chunked according to the given chunking scheme.
 
         Args:
             name: The name of the DataArray.
+            chunks: A mapping of dimension names to the size of the chunks
+                along the dimensions.
 
         See Also:
-        - https://docs.xarray.dev/en/stable/user-guide/io.html#distributed-writes
+            - https://docs.xarray.dev/en/stable/user-guide/io.html#distributed-writes
         """
         # Create a dask array of zeros with the shape of the dataset
         # * The values of this are ignored, only the shape and chunks are used
         dummy_values = dask.array.zeros(  # type: ignore
             shape=list(self.shapemap.values()),
-            chunks=tuple([self.default_chunking()[k] for k in self.shapemap]),
+            chunks=tuple([chunks[k] for k in self.shapemap]),
         )
         attrs: dict[str, str] = {
             "produced_by": "".join((

src/nwp_consumer/internal/entities/modelmetadata.py

@@ -55,6 +55,15 @@ class ModelMetadata:
     Which prints grid data from the grib file.
     """
 
+    chunk_count_overrides: dict[str, int] = dataclasses.field(default_factory=dict)
+    """Mapping of dimension names to the desired number of chunks in that dimension.
+
+    Overrides the default chunking strategy.
+
+    See Also:
+        - `entities.coordinates.NWPDimensionCoordinateMap.chunking`
+    """
+
     def __str__(self) -> str:
         """Return a pretty-printed string representation of the metadata."""
         pretty: str = "".join((
@@ -93,13 +102,14 @@ def with_region(self, region: str) -> "ModelMetadata":
                 log.warning(f"Unknown region '{region}', not cropping expected coordinates.")
                 return self
 
-    def set_maximum_number_of_chunks_in_one_dim(self, maximum_number_of_chunks_in_one_dim: int) \
-            -> "ModelMetadata":
-        """Set the maximum number of chunks in one dimension."""
-        self.expected_coordinates.maximum_number_of_chunks_in_one_dim \
-            = maximum_number_of_chunks_in_one_dim
-        return self
-
+    def with_chunk_count_overrides(self, overrides: dict[str, int]) -> "ModelMetadata":
+        """Returns metadata for the given model with the given chunk count overrides."""
+        if not set(overrides.keys()).issubset(self.expected_coordinates.dims):
+            log.warning(
+                "Chunk count overrides contain keys not in the expected coordinates. "
+                "These will not modify the chunking strategy.",
+            )
+        return dataclasses.replace(self, chunk_count_overrides=overrides)
 
 class Models:
     """Namespace containing known models."""

src/nwp_consumer/internal/entities/tensorstore.py

@@ -16,7 +16,7 @@
 import os
 import pathlib
 import shutil
-from collections.abc import MutableMapping
+from collections.abc import Mapping, MutableMapping
 from typing import Any
 
 import pandas as pd
@@ -77,6 +77,7 @@ def initialize_empty_store(
         model: str,
         repository: str,
         coords: NWPDimensionCoordinateMap,
+        chunks: dict[str, int],
     ) -> ResultE["TensorStore"]:
         """Initialize a store for a given init time.
 
@@ -110,6 +111,7 @@ def initialize_empty_store(
                    This is also used as the name of the tensor.
             repository: The name of the repository providing the tensor data.
             coords: The coordinates of the store.
+            chunks: The chunk sizes for the store.
 
         Returns:
             An indicator of a successful store write containing the number of bytes written.
@@ -152,7 +154,8 @@ def initialize_empty_store(
         # Write the coordinates to a skeleton Zarr store
         # * 'compute=False' enables only saving metadata
         # * 'mode="w-"' fails if it finds an existing store
-        da: xr.DataArray = coords.as_zeroed_dataarray(name=model)
+
+        da: xr.DataArray = coords.as_zeroed_dataarray(name=model, chunks=chunks)
         encoding = {
             model: {"write_empty_chunks": False},
             "init_time": {"units": "nanoseconds since 1970-01-01"},
@@ -257,22 +260,52 @@ def write_to_region(
         If the region dict is empty or not provided, the region is determined
         via the 'determine_region' method.
 
+        This function should be thread safe, so a check is performed on the region
+        to ensure that it can be safely written to in parallel, i.e. that it covers
+        an integer number of chunks.
+
         Args:
             da: The data to write to the store.
             region: The region to write to.
 
         Returns:
             An indicator of a successful store write containing the number of bytes written.
+
+        See Also:
+            - https://docs.xarray.dev/en/stable/user-guide/io.html#distributed-writes
         """
         # Attempt to determine the region if missing
         if region is None or region == {}:
             region_result = NWPDimensionCoordinateMap.from_xarray(da).bind(
                 self.coordinate_map.determine_region,
             )
             if isinstance(region_result, Failure):
-                return Failure(region_result.failure())
+                return region_result
             region = region_result.unwrap()
 
+        # For each dimensional slice defining the region, check the slice represents an
+        # integer number of chunks along that dimension.
+        # * This is to ensure that the data can safely be written in parallel.
+        # * The start and and of each slice should be divisible by the chunk size.
+        chunksizes: Mapping[Any, tuple[int, ...]] = xr.open_dataarray(
+            self.path, engine="zarr",
+        ).chunksizes
+        for dim, slc in region.items():
+            chunk_size = chunksizes.get(dim, (1,))[0]
+            # TODO: Determine if this should return a full failure object
+            if slc.start % chunk_size != 0 or slc.stop % chunk_size != 0:
+                log.warning(
+                    f"Determined region of raw data to be written for dimension '{dim}'"
+                    f"does not align with chunk boundaries of the store. "
+                    f"Dimension '{dim}' has a chunk size of {chunk_size}, "
+                    "but the data to be written for this dimension starts at chunk "
+                    f"{slc.start / chunk_size:.2f} (index {slc.start}) and ends at chunk "
+                    f"{slc.stop / chunk_size:.2f} (index {slc.stop}). "
+                    "As such, this region cannot be safely written in parallel. "
+                    "Ensure the chunking is granular enough to cover the raw data region.",
+                )
+
+
         # Perform the regional write
         try:
             da.to_zarr(store=self.path, region=region, consolidated=True)

src/nwp_consumer/internal/entities/test_tensorstore.py

@@ -89,6 +89,7 @@ def store(self, year: int) -> Generator[TensorStore, None, None]:
             model="test_da",
             repository="dummy_repository",
             coords=test_coords,
+            chunks=test_coords.chunking(chunk_count_overrides={}),
         )
         self.assertIsInstance(init_result, Success, msg=init_result)
         store = init_result.unwrap()

src/nwp_consumer/internal/repositories/raw_repositories/ceda_ftp.py

@@ -121,7 +121,10 @@ def repository() -> entities.RawRepositoryMetadata:
             optional_env={},
             postprocess_options=entities.PostProcessOptions(),
             available_models={
-                "default": entities.Models.MO_UM_GLOBAL_17KM,
+                "default": entities.Models.MO_UM_GLOBAL_17KM.with_chunk_count_overrides({
+                    "latitude": 8,
+                    "longitude": 8,
+                }),
             },
         )
 

src/nwp_consumer/internal/repositories/raw_repositories/ecmwf_realtime.py

@@ -83,10 +83,8 @@ def repository() -> entities.RawRepositoryMetadata:
             },
             postprocess_options=entities.PostProcessOptions(),
             available_models={
-                "default": entities.Models.ECMWF_HRES_IFS_0P1DEGREE.with_region("uk")
-                .set_maximum_number_of_chunks_in_one_dim(2),
-                "hres-ifs-uk": entities.Models.ECMWF_HRES_IFS_0P1DEGREE.with_region("uk")
-                .set_maximum_number_of_chunks_in_one_dim(2),
+                "default": entities.Models.ECMWF_HRES_IFS_0P1DEGREE.with_region("uk"),
+                "hres-ifs-uk": entities.Models.ECMWF_HRES_IFS_0P1DEGREE.with_region("uk"),
                 "hres-ifs-india": entities.Models.ECMWF_HRES_IFS_0P1DEGREE.with_region("india"),
             },
         )
@@ -196,17 +194,18 @@ def _download(self, url: str) -> ResultE[pathlib.Path]:
         ).with_suffix(".grib").expanduser()
 
         # Only download the file if not already present
-        log.info("Checking for local file: '%s'", local_path)
-        if not local_path.exists() or local_path.stat().st_size == 0:
+        if local_path.exists() and local_path.stat().st_size > 0:
+            log.debug("Skipping download for existing file at '%s'.", local_path.as_posix())
+        else:
             local_path.parent.mkdir(parents=True, exist_ok=True)
             log.debug("Requesting file from S3 at: '%s'", url)
 
             try:
                 if not self._fs.exists(url):
                     raise FileNotFoundError(f"File not found at '{url}'")
 
+                log.debug("Writing file from '%s' to '%s'", url, local_path.as_posix())
                 with local_path.open("wb") as lf, self._fs.open(url, "rb") as rf:
-                    log.info(f"Writing file from {url} to {local_path}")
                     for chunk in iter(lambda: rf.read(12 * 1024), b""):
                         lf.write(chunk)
                         lf.flush()

src/nwp_consumer/internal/services/consumer_service.py

@@ -106,13 +106,12 @@ def _parallelize_generator[T](
             max_connections: The maximum number of connections to use.
         """
         # TODO: Change this based on threads instead of CPU count
+        # TODO: Enable choosing between threads and processes?
         n_jobs: int = max(cpu_count() - 1, max_connections)
         prefer = "threads"
 
-        concurrency = os.getenv("CONCURRENCY", "True").capitalize() == "False"
-        if concurrency:
+        if os.getenv("CONCURRENCY", "True").capitalize() == "False":
             n_jobs = 1
-            prefer = "processes"
 
         log.debug(f"Using {n_jobs} concurrent {prefer}")
 
@@ -156,6 +155,9 @@ def _create_suitable_store(
                 model_metadata.expected_coordinates,
                 init_time=its,
             ),
+            chunks=model_metadata.expected_coordinates.chunking(
+                chunk_count_overrides=model_metadata.chunk_count_overrides,
+            ),
         )
 
     @override