issues

^{Originally posted by **ilan-gold** February 15, 2024} My goal is to get a dataset from [custom io-zarr backend lazy-loaded](https://docs.xarray.dev/en/stable/internals/how-to-add-new-backend.html#how-to-support-lazy-loading). But when I declare a `DataArray` based on the `Variable` which uses `LazilyIndexedArray`, everything is read in. Is this expected? I specifically don't want to have to use dask if possible. I have seen https://github.com/aurghs/xarray-backend-tutorial/blob/main/2.Backend_with_Lazy_Loading.ipynb but it's a little bit different. While I have a custom backend array inheriting from `ZarrArrayWrapper`, this example using `ZarrArrayWrapper` directly still highlights the same unexpected behavior of everything being read in. ```python import zarr import xarray as xr from tempfile import mkdtemp import numpy as np from pathlib import Path from collections import defaultdict class AccessTrackingStore(zarr.DirectoryStore): def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs) self._access_count = {} self._accessed = defaultdict(set) def __getitem__(self, key): for tracked in self._access_count: if tracked in key: self._access_count[tracked] += 1 self._accessed[tracked].add(key) return super().__getitem__(key) def get_access_count(self, key): return self._access_count[key] def set_key_trackers(self, keys_to_track): if isinstance(keys_to_track, str): keys_to_track = [keys_to_track] for k in keys_to_track: self._access_count[k] = 0 def get_subkeys_accessed(self, key): return self._accessed[key] orig_path = Path(mkdtemp()) z = zarr.group(orig_path / "foo.zarr") z['array'] = np.random.randn(1000, 1000) store = AccessTrackingStore(orig_path / "foo.zarr") store.set_key_trackers(['array']) z = zarr.group(store) arr = xr.backends.zarr.ZarrArrayWrapper(z['array']) lazy_arr = xr.core.indexing.LazilyIndexedArray(arr) # just `.zarray` var = xr.Variable(('x', 'y'), lazy_arr) print('Variable read in ', store.get_subkeys_accessed('array')) # now everything is read in da = xr.DataArray(var) print('DataArray read in ', store.get_subkeys_accessed('array')) ```