issues: 290084668

Code Sample, a copy-pastable example if possible

I am trying to open several ocean model data files. During the model run additional variables were written to the files. So for instance the first file will look like this:

<xarray.Dataset> Dimensions: (st_edges_ocean: 51, st_ocean: 50, time: 1, xt_ocean: 3600, yt_ocean: 2700) Coordinates: * xt_ocean (xt_ocean) float64 -279.9 -279.8 -279.7 -279.6 -279.5 ... * yt_ocean (yt_ocean) float64 -81.11 -81.07 -81.02 -80.98 -80.94 ... * time (time) float64 4.401e+04 * st_ocean (st_ocean) float64 5.034 15.1 25.22 35.36 45.58 55.85 ... * st_edges_ocean (st_edges_ocean) float64 0.0 10.07 20.16 30.29 40.47 ... Data variables: jp_recycle (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jp_reminp (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jp_uptake (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jo2 (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> dic_stf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> o2_stf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> Attributes: filename: 01210101.ocean_minibling_term_src.nc title: CM2.6_miniBling grid_type: mosaic grid_tile: 1 and the last file will look like this (with additional data variables o2_btf, dic_btf, and 'po4_btf`). ```

<xarray.Dataset> Dimensions: (st_edges_ocean: 51, st_ocean: 50, time: 1, xt_ocean: 3600, yt_ocean: 2700) Coordinates: * xt_ocean (xt_ocean) float64 -279.9 -279.8 -279.7 -279.6 -279.5 ... * yt_ocean (yt_ocean) float64 -81.11 -81.07 -81.02 -80.98 -80.94 ... * st_ocean (st_ocean) float64 5.034 15.1 25.22 35.36 45.58 55.85 ... * st_edges_ocean (st_edges_ocean) float64 0.0 10.07 20.16 30.29 40.47 ... * time (time) float64 7.25e+04 Data variables: jp_recycle (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jp_reminp (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jp_uptake (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> jo2 (time, st_ocean, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 50, 2700, 3600), chunksize=(1, 1, 2700, 3600)> dic_stf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> dic_btf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> o2_stf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> o2_btf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> po4_btf (time, yt_ocean, xt_ocean) float64 dask.array<shape=(1, 2700, 3600), chunksize=(1, 2700, 3600)> Attributes: date: created 2014-01-08 program: time_average_netcdf.rb history: Perform time-means on all variables in 01990101.ocean_minibli... filename: 01990101.ocean_minibling_term_src.nc title: CM2.6_miniBling grid_type: mosaic grid_tile: 1 `` If I specify the additional variables to be dropped, reading all files withxarray.open_mfdataset` works like a charm. But without specifying the variables to be dropped it takes an excruciating amount of time to load.

First of all, I was wondering if there would be the possibility to display a warning if this situation occurs, suggesting to add these variables as drop_variables keyword. That would have saved me a ton of digging time.

Even better would be some way to read such datasets in a fast manner. If we could specify a fastpath option (like suggested in #1823), perhaps this could speed this task up (given that all dimensions stay the same)?