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/5219#issuecomment-839106491,https://api.github.com/repos/pydata/xarray/issues/5219,839106491,MDEyOklzc3VlQ29tbWVudDgzOTEwNjQ5MQ==,1197350,2021-05-11T20:08:27Z,2021-05-11T20:08:27Z,MEMBER,"> Instead we could require explicitly supplying `chunks` vis the `encoding` parameter in the `to_zarr()` call.

This could also break existing workflows though. For example, pangeo-forge is using the encoding.chunks attribute to specify target dataset chunks.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,868352536
https://github.com/pydata/xarray/issues/5219#issuecomment-828071017,https://api.github.com/repos/pydata/xarray/issues/5219,828071017,MDEyOklzc3VlQ29tbWVudDgyODA3MTAxNw==,1197350,2021-04-28T01:26:34Z,2021-04-28T01:26:34Z,MEMBER,"> we probably would NOT want to use `safe_chunks=False`, correct?

correct

The problem in this issue is that the dataset is carrying around its original chunks in `.encoding` and then xarray tries to use these values to set the chunk encoding on the second write op. The solution is to *manually delete the chunk encoding from all your data variables*. Something like
```python
for var in ds:
    del ds[var].encoding['chunks']
```

Originally part of #5056 was a change that would have xarray automatically do this deletion after some operations (such as calling `.chunk()`);  however, we could not reach a consensus on the best way to implement that change. Your example is interesting because it is a slightly different scenario -- calling `sel()` instead of `chunk()` -- but the root cause appears to be the same: `encoding['chunks']` is being kept around too conservatively.","{""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,868352536