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[WIP] Use zarr internal LRU caching #2814

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[WIP] Use zarr internal LRU caching #2814

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5ab07f8
added protect_dataset_variables_inplace to open_zarr
rabernat Mar 14, 2019
e92f9c1
use zarr LRU cache
rabernat Mar 14, 2019
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17 changes: 13 additions & 4 deletions xarray/backends/zarr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
from ..core.pycompat import integer_types
from ..core.utils import FrozenOrderedDict, HiddenKeyDict
from .common import AbstractWritableDataStore, BackendArray
from .api import _protect_dataset_variables_inplace

# need some special secret attributes to tell us the dimensions
_DIMENSION_KEY = '_ARRAY_DIMENSIONS'
Expand Down Expand Up @@ -355,7 +356,8 @@ def close(self):
def open_zarr(store, group=None, synchronizer=None, auto_chunk=True,
decode_cf=True, mask_and_scale=True, decode_times=True,
concat_characters=True, decode_coords=True,
drop_variables=None, consolidated=False):
drop_variables=None, consolidated=False, cache=False,
max_cache_size=None):
"""Load and decode a dataset from a Zarr store.

.. note:: Experimental
Expand Down Expand Up @@ -408,6 +410,12 @@ def open_zarr(store, group=None, synchronizer=None, auto_chunk=True,
consolidated : bool, optional
Whether to open the store using zarr's consolidated metadata
capability. Only works for stores that have already been consolidated.
cache : bool, optional
If True, the zarr store is wrapped with a
``zarr.storage.LRUStoreCache``.
max_cache_size : int, optional
The maximum size that the cache may grow to, in number of bytes.
Provide `None` if you would like the cache to have unlimited size.

Returns
-------
Expand All @@ -434,11 +442,12 @@ def maybe_decode_store(store, lock=False):
store, mask_and_scale=mask_and_scale, decode_times=decode_times,
concat_characters=concat_characters, decode_coords=decode_coords,
drop_variables=drop_variables)

# TODO: this is where we would apply caching

return ds

if cache:
import zarr
store = zarr.LRUStoreCache(store, max_size=max_cache_size)

# Zarr supports a wide range of access modes, but for now xarray either
# reads or writes from a store, never both. For open_zarr, we only read
mode = 'r'
Expand Down