html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/2300#issuecomment-673565228,https://api.github.com/repos/pydata/xarray/issues/2300,673565228,MDEyOklzc3VlQ29tbWVudDY3MzU2NTIyOA==,4441338,2020-08-13T16:04:04Z,2020-08-13T16:04:04Z,NONE,"I arrived here due to a different use case / problem, which ultimately I solved, but I think there's value in documenting it here.
My use case is the following workflow: 
1 . take raw data, build a dataset, append it to a zarr store Z
2 . analyze the data on Z, then maybe goto 1.
Step 2's performance is much better when data on Z is chunked properly along the appending dimension 'frame' (chunks of size 50), however step 1 only adds 1 element along it. I end up with Z having chunks (1,1,1,1,1...) on 'frame'. 
On xarray 0.16.0, this seems solvable via the encoding parameter, if we take care to only use it on the store creation.
Before that version, I was using something like the monkey patch posted by @chrisbarber .
Code:
```python
import shutil
import xarray as xr
import numpy as np
import tempfile
zarr_path = tempfile.mkdtemp()

def append_test(ds,chunks):
    shutil.rmtree(zarr_path)
    
    for i in range(21):
        d = ds.isel(frame=slice(i,i+1))
        d = d.chunk(chunks)
        d.to_zarr(zarr_path,consolidated=True,**(dict(mode='a',append_dim='frame') if i>0 else {}))
    dsa = xr.open_zarr(str(zarr_path),consolidated=True)
    print(dsa.chunks,dsa.dims)
    
#sometime before 0.16.0
import contextlib
@contextlib.contextmanager
def change_determine_zarr_chunks(chunks):
    orig_determine_zarr_chunks = xr.backends.zarr._determine_zarr_chunks
    try:
        def new_determine_zarr_chunks( enc_chunks, var_chunks, ndim, name):
            da = ds[name]
            zchunks = tuple(chunks[dim] if (dim in chunks and chunks[dim] is not None) else da.shape[i] for i,dim in enumerate(da.dims))
            return zchunks
        xr.backends.zarr._determine_zarr_chunks = new_determine_zarr_chunks
        yield
    finally:
        xr.backends.zarr._determine_zarr_chunks = orig_determine_zarr_chunks
chunks = {'frame':10,'other':50}
ds = xr.Dataset({'data':xr.DataArray(data=np.random.rand(100,100),dims=('frame','other'))})

append_test(ds,chunks)
with change_determine_zarr_chunks(chunks):
    append_test(ds,chunks)

#with 0.16.0
def append_test_encoding(ds,chunks):
    shutil.rmtree(zarr_path)
    
    encoding = {}
    for k,v in ds.variables.items():
        encoding[k]={'chunks':tuple(chunks[dk] if dk in chunks else v.shape[i] for i,dk in enumerate(v.dims))}
    
    for i in range(21):
        d = ds.isel(frame=slice(i,i+1))
        d = d.chunk(chunks)
        d.to_zarr(zarr_path,consolidated=True,**(dict(mode='a',append_dim='frame') if i>0 else dict(encoding = encoding)))
    dsa = xr.open_zarr(str(zarr_path),consolidated=True)
    print(dsa.chunks,dsa.dims)

append_test_encoding(ds,chunks)
```

```
Frozen(SortedKeysDict({'frame': (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), 'other': (50, 50)})) Frozen(SortedKeysDict({'frame': 21, 'other': 100}))
Frozen(SortedKeysDict({'frame': (10, 10, 1), 'other': (50, 50)})) Frozen(SortedKeysDict({'frame': 21, 'other': 100}))
Frozen(SortedKeysDict({'frame': (10, 10, 1), 'other': (50, 50)})) Frozen(SortedKeysDict({'frame': 21, 'other': 100}))
```
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