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Enforce rechunking for sharded Icechunk store #897

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Enforce rechunking for sharded Icechunk store #897

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c441bd5
enforce sharded chunks during icechunk write
Apr 20, 2026
b08e551
added test with sharded icechunk Zarr store
Apr 20, 2026
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4 changes: 4 additions & 0 deletions cubed/icechunk.py
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,10 @@ def store_icechunk(

arrays = []
for source, target, region in zip(sources, targets, regions_list):
sharding_enabled = target.shards is not None
sharding_misaligned = target.shards != source.chunks
if sharding_enabled and sharding_misaligned:
source = source.rechunk(target.shards)
array = _store_array(
source,
target,
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39 changes: 37 additions & 2 deletions cubed/tests/test_icechunk.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ def icechunk_storage(tmpdir) -> "Storage":
return Storage.new_local_filesystem(str(tmpdir))


def create_icechunk(a, icechunk_storage, /, *, dtype=None, chunks=None):
def create_icechunk(a, icechunk_storage, /, *, dtype=None, chunks=None, shards=None):
# from dask.asarray
if not isinstance(getattr(a, "shape", None), Iterable):
# ensure blocks are arrays
Expand All @@ -44,7 +44,9 @@ def create_icechunk(a, icechunk_storage, /, *, dtype=None, chunks=None):
store = session.store

group = zarr.group(store=store, overwrite=True)
arr = group.create_array("a", shape=a.shape, dtype=dtype, chunks=chunks)
arr = group.create_array(
"a", shape=a.shape, dtype=dtype, chunks=chunks, shards=shards
)

arr[...] = a

Expand Down Expand Up @@ -136,3 +138,36 @@ def test_store_icechunk_region(icechunk_storage, executor):
]
),
)


def test_store_icechunk_sharded(icechunk_storage, executor):
a = xp.asarray(
[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]],
chunks=(2, 2),
)
create_icechunk(
np.zeros((4, 4), dtype=int), icechunk_storage, chunks=(2, 2), shards=(4, 4)
)

# note that the same zarr store is overwritten in the following tests

repo = Repository.open(storage=icechunk_storage)
session = repo.writable_session("main")
fork = session.fork()
store = fork.store
group = zarr.open_group(store=store)
target = group.get("a")
merged_session = store_icechunk(sources=a, targets=target, executor=executor)
session.merge(merged_session)
session.commit("commit 1")

# reopen store and check contents of array
repo = Repository.open(icechunk_storage)
session = repo.readonly_session(branch="main")
store = session.store

group = zarr.open_group(store=store, mode="r")
assert_array_equal(
cubed.from_array(group["a"])[:],
a,
)
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