id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
1778486450,PR_kwDOAMm_X85UHfL4,7948,Implement preferred_chunks for netcdf 4 backends,167802,closed,0,,,10,2023-06-28T08:43:30Z,2023-09-12T09:01:03Z,2023-09-11T23:05:49Z,CONTRIBUTOR,,0,pydata/xarray/pulls/7948,"According to the `open_dataset` documentation, using `chunks=""auto""` or `chunks={}` should yield datasets with variables chunked depending on the preferred chunks of the backend. However neither the netcdf4 nor the h5netcdf backend seem to implement the `preferred_chunks` encoding attribute needed for this to work.

This PR adds this attribute to the encoding upon data reading. This results in `chunks=""auto""` in `open_dataset` returning variables with chunk sizes multiples of the chunks in the nc file, and for `chunks={}`, returning the variables with then exact nc chunk sizes.  

- [x] Closes #1440
- [x] Tests added
- [ ] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
- [ ] New functions/methods are listed in `api.rst`
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387732534,MDExOlB1bGxSZXF1ZXN0MjM2MTU0NTUz,2591,Fix h5netcdf saving scalars with filters or chunks,167802,closed,0,,,8,2018-12-05T12:22:40Z,2018-12-11T07:27:27Z,2018-12-11T07:24:36Z,CONTRIBUTOR,,0,pydata/xarray/pulls/2591," - [x] Closes #2563
 - [x] Tests added (for all bug fixes or enhancements)
 - [x] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API (remove if this change should not be visible to users, e.g., if it is an internal clean-up, or if this is part of a larger project that will be documented later)
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