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/6433#issuecomment-1085774334,https://api.github.com/repos/pydata/xarray/issues/6433,1085774334,IC_kwDOAMm_X85At5n-,2448579,2022-04-01T11:15:38Z,2022-04-01T11:15:38Z,MEMBER,">  open_mfdataset(..., parallel=True) computed the whole dataset eagerly

This isn't  totally true. It'll should only compute and save  when comparing coordinate variables for equality as part  of the concatenation step (yes, bad default!). See the [note here](https://docs.xarray.dev/en/stable/user-guide/io.html#reading-multi-file-datasets).

 The code is https://github.com/pydata/xarray/blob/305533d585389f7240ae2383a323337d4761d33a/xarray/core/concat.py#L340-L360","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1188965542
https://github.com/pydata/xarray/issues/6433#issuecomment-1085589487,https://api.github.com/repos/pydata/xarray/issues/6433,1085589487,IC_kwDOAMm_X85AtMfv,14808389,2022-04-01T08:21:36Z,2022-04-01T09:19:14Z,MEMBER,"`parallel=True` will *open* (read the metadata) and preprocess the datasets in parallel using `dask`, which will happen in sequence with `parallel=False`. The difference is [roughly](https://github.com/pydata/xarray/blob/305533d585389f7240ae2383a323337d4761d33a/xarray/backends/api.py#L896-L916):
```python
if parallel:
    datasets, = dask.compute([dask.delayed(xr.open_dataset)(path, *args, **kwargs) for path in paths])
else:
    datasets = [xr.open_dataset(path, *args, **kwargs) for path in paths]
```
So unlike `load_dataset` / the proposed `load_mfdataset` this will read metadata but not the actual data, and the result should be the same regardless of the `parallel` parameter (if it doesn't that would be a bug).

I agree that we could improve the parameter description, though.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1188965542